Hard to overstate the significance of this topic. Unfortunately, the material in here will become more and more depressing as time goes on. Not much hope of any alternative to that.


Postby admin » Thu Jun 18, 2015 5:41 am


March 9, 2015



Temperature data from four international science institutions. All show rapid warming in the past few decades and that the last decade has been the warmest on record.

Ninety-seven percent of climate scientists agree that climate-warming trends over the past century are very likely due to human activities, [1] and most of the leading scientific organizations worldwide have issued public statements endorsing this position. The following is a partial list of these organizations, along with links to their published statements and a selection of related resources.


Statement on climate change from 18 scientific associations

"Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver." (2009) [2]

American Association for the Advancement of Science

"The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society." (2006) [3]

American Chemical Society

"Comprehensive scientific assessments of our current and potential future climates clearly indicate that climate change is real, largely attributable to emissions from human activities, and potentially a very serious problem." (2004) [4]

American Geophysical Union

"Human-induced climate change requires urgent action. Humanity is the major influence on the global climate change observed over the past 50 years. Rapid societal responses can significantly lessen negative outcomes." (Adopted 2003, revised and reaffirmed 2007, 2012, 2013) [5]

American Medical Association

"Our AMA ... supports the findings of the Intergovernmental Panel on Climate Change's fourth assessment report and concurs with the scientific consensus that the Earth is undergoing adverse global climate change and that anthropogenic contributions are significant." (2013) [6]

American Meteorological Society

"It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide." (2012) [7]

American Physical Society

"The evidence is incontrovertible: Global warming is occurring. If no mitigating actions are taken, significant disruptions in the Earth's physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now." (2007) [8]

The Geological Society of America

"The Geological Society of America (GSA) concurs with assessments by the National Academies of Science (2005), the National Research Council (2006), and the Intergovernmental Panel on Climate Change (IPCC, 2007) that global climate has warmed and that human activities (mainly greenhouse-gas emissions) account for most of the warming since the middle 1900s." (2006; revised 2010) [9]


International academies: Joint statement

"Climate change is real. There will always be uncertainty in understanding a system as complex as the world's climate. However there is now strong evidence that significant global warming is occurring. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities (IPCC 2001)." (2005, 11 international science academies) [10]

U.S. National Academy of Sciences

"The scientific understanding of climate change is now sufficiently clear to justify taking steps to reduce the amount of greenhouse gases in the atmosphere." (2005) [11]


U.S. Global Change Research Program

"The global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Human 'fingerprints' also have been identified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture, and Arctic sea ice." (2009, 13 U.S. government departments and agencies) [12]


Intergovernmental Panel on Climate Change

“Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level." [13]

Most of the observed increase in global average temperatures since the mid-20th century is very likely* due to the observed increase in anthropogenic greenhouse gas concentrations." [14]


*IPCC defines 'very likely' as greater than 90 percent probability of occurrence.


List of worldwide scientific organizations

The following page lists the nearly 200 worldwide scientific organizations that hold the position that climate change has been caused by human action.

U.S. agencies

The following page contains information on what federal agencies are doing to adapt to climate change. ... tation.pdf


1. W. R. L. Anderegg, “Expert Credibility in Climate Change,” Proceedings of the National Academy of Sciences Vol. 107 No. 27, 12107-12109 (21 June 2010); DOI: 10.1073/pnas.1003187107.

P. T. Doran & M. K. Zimmerman, "Examining the Scientific Consensus on Climate Change," Eos Transactions American Geophysical Union Vol. 90 Issue 3 (2009), 22; DOI: 10.1029/2009EO030002.

N. Oreskes, “Beyond the Ivory Tower: The Scientific Consensus on Climate Change,” Science Vol. 306 no. 5702, p. 1686 (3 December 2004); DOI: 10.1126/science.1103618.

2. Statement on climate change from 18 scientific associations (2009)

American Association for the Advancement of Science
American Chemical Society
American Geophysical Union
American Institute of Biological Sciences
American Meteorological Society
American Society of Agronomy
American Society of Plant Biologists
American Statistical Association
Association of Ecosystem Research Centers
Botanical Society of America
Crop Science Society of America
Ecological Society of America
Natural Science Collections Alliance
Organization of Biological Field Stations
Society for Industrial and Applied Mathematics
Society of Systematic Biologists
Soil Science Society of America
University Corporation for Atmospheric Research

1200 New York Avenue, NW, Washington, DC 20005 USA
Tel: 202 326 6600 Fax: 202 289 4950

October 21, 2009

Dear Senator:

As you consider climate change legislation, we, as leaders of scientific organizations, write to state the consensus scientific view.

Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver. These conclusions are based on multiple independent lines of evidence, and contrary assertions are inconsistent with an objective assessment of the vast body of peer- reviewed science. Moreover, there is strong evidence that ongoing climate change will have broad impacts on society, including the global economy and on the environment. For the United States, climate change impacts include sea level rise for coastal states, greater threats of extreme weather events, and increased risk of regional water scarcity, urban heat waves, western wildfires, and the disturbance of biological systems throughout the country. The severity of climate change impacts is expected to increase substantially in the coming decades. [1]

If we are to avoid the most severe impacts of climate change, emissions of greenhouse gases must be dramatically reduced. In addition, adaptation will be necessary to address those impacts that are already unavoidable. Adaptation efforts include improved infrastructure design, more sustainable management of water and other natural resources, modified agricultural practices, and improved emergency responses to storms, floods, fires and heat waves.

We in the scientific community offer our assistance to inform your deliberations as you seek to address the impacts of climate change.

Timothy L. Grove, President, American Geophysical Union
Keith Seitter, Executive Director, American Meteorological Society
Tuan-hua David Ho, President, American Society of Plant Biologists
Lucinda Johnson, President, Association of Ecosystem Research Centers
Thomas Lane, President, American Chemical Society
May R. Berenbaum, President, American Institute of Biological Sciences
Mark Alley, President, American Society of Agronomy
Sally C. Morton, President, American Statistical Association
Kent E. Holsinger, President, Botanical Society of America



1. The conclusions in this paragraph reflect the scientific consensus represented by, for example, the Intergovernmental Panel on Climate Change and U.S. Global Change Research Program. Many scientific societies have endorsed these findings in their own statements, including the American Association for the Advancement of Science, American Chemical Society, American Geophysical Union, American Meteorological Society, and American Statistical Association.

3. AAAS Board Statement on Climate Change (2006)

Embargoed: Not for release until 12:30 p.m. Pacific Standard Time
Sunday, 18 February 2007

AAS Board Statement on Climate Change

Approved by the Board of Directors, American Association for the Advancement of Science

9 December 2006

The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society. Accumulating data from across the globe reveal a wide array of effects: rapidly melting glaciers, destabilization of major ice sheets, increases in extreme weather, rising sea level, shifts in species ranges, and more. The pace of change and the evidence of harm have increased markedly over the last five years. The time to control greenhouse gas emissions is now.

The atmospheric concentration of carbon dioxide, a critical greenhouse gas, is higher than it has been for at least 650,000 years. The average temperature of the Earth is heading for levels not experienced for millions of years. Scientific predictions of the impacts of increasing atmospheric concentrations of greenhouse gases from fossil fuels and deforestation match observed changes. As expected, intensification of droughts, heat waves, floods, wildfires, and severe storms is occurring, with a mounting toll on vulnerable ecosystems and societies. These events are early warning signs of even more devastating damage to come, some of which will be irreversible.

Delaying action to address climate change will increase the environmental and societal consequences as well as the costs. The longer we wait to tackle climate change, the harder and more expensive the task will be.

History provides many examples of society confronting grave threats by mobilizing knowledge and promoting innovation. We need an aggressive research, development and deployment effort to transform the existing and future energy systems of the world away from technologies that emit greenhouse gases. Developing clean energy technologies will provide economic opportunities and ensure future energy supplies.

In addition to rapidly reducing greenhouse gas emissions, it is essential that we develop strategies to adapt to ongoing changes and make communities more resilient to future changes.

The growing torrent of information presents a clear message: we are already experiencing global climate change. It is time to muster the political will for concerted action. Stronger leadership at all levels is needed. The time is now. We must rise to the challenge. We owe this to future generations.

The conclusions in this statement reflect the scientific consensus represented by, for example, the Intergovernmental Panel on Climate Change (, and the Joint National Academies' statement (http://nationalacademies. org/onpi/06072005.pdf).

AAAS Board Statement on Climate Change

Approved by the AAAS Board of Directors
9 December 2006

Gilbert S. Omenn, Chair, AAAS Board
University of Michigan Health System

John Holdren, AAAS President
Harvard University and The Woods Hole Research Center

David Baltimore, AAAS President-Elect
California Institute of Technology

David E. Shaw, AAAS Treasurer
D.E. Shaw & Co., Inc.

William T. Golden, AAAS Treasurer Emeritus

Alan I. Leshner, AAAS Chief Executive Officer

Rosina M. Bierbaum, University of Michigan

John E. Dowling, Harvard University

Lynn Enquist, Princeton University

Dr. Susan Fitzpatrick, James S. McDonnell Foundation

Dr. Alice Gast, Lehigh University

Dr. Thomas D. Pollard, Yale University

Dr. Peter R. Stang, University of Utah

Dr. Kathryn D. Sullivan, Ohio State University

4. ACS Public Policy Statement: Climate Change (2010-2013)

Global Climate Change

ACS Position Statement

"Careful and comprehensive scientific assessments have clearly demonstrated that the Earth’s climate system is changing in response to growing atmospheric burdens of greenhouse gases (GHGs) and absorbing aerosol particles.” (IPCC, 2007) “Climate change is occurring, is caused largely by human activities, and poses significant risks for—and in many cases is already affecting—a broad range of human and natural systems.” (NRC, 2010a) “The potential threats are serious and actions are required to mitigate climate change risks and to adapt to deleterious climate change impacts that probably cannot be avoided.” (NRC, 2010b, c)

This statement reviews key probable climate change impacts and recommends actions required to mitigate or adapt to current and anticipated consequences.

Climate Change Impacts

The Earth's climate is the product of complex, highly dynamic, and often nonlinear, interactions among physical, chemical, and biological processes occurring at many scales in the atmosphere; at terrestrial, fresh water and marine surfaces; and in the depths of the oceans and landforms. While recent research advances in Earth systems science have greatly strengthened our understanding of prior and current climate properties and processes, our ability to quantitatively predict how the future climate will respond to continued and increasing greenhouse-gas and fine-particle emissions is still limited. Even more limited is our ability to precisely predict how the Earth's ecological and human systems will respond to climate changes.

However, comprehensive scientific assessments of our current and potential future climates clearly indicate that climate change is real, largely attributable to emissions from human activities, and potentially a very serious problem. This sober conclusion has been recently reconfirmed by an in-depth set of studies focused on “America’s Climate Choices” (ACC) conducted by the U.S. National Academies (NRC, 2010a, b, c, d). The ACC studies, performed by independent and highly respected teams of scientists, engineers, and other skilled professionals, reached the same general conclusions that were published in the latest comprehensive assessment conducted by the International Panel on Climate Change (IPCC, 2007). Recently, some errors in the IPCC (2007) reports have been acknowledged and questions about the transparency of the IPCC process have been raised. An independent review by the InterAcademy Council (IAC), a collaboration of the world's leading national science academies, found "that the IPCC assessment process has been successful overall and has served society well," and that "through its unique partnership between scientists and governments, the IPCC has heightened public awareness of climate change, raised the level of scientific debate, and influenced the science agendas of many nations." (IAC, 2010) The IAC also recommended managerial and procedural improvements that would strengthen future assessments.

The range of observed and potential climate change impacts identified by the ACC assessment include a warmer climate with more extreme weather events, significant sea level rise, more constrained fresh water sources, deterioration or loss of key land and marine ecosystems, and reduced food resources— many of which may pose serious public health threats. (NRC, 2010a) The effects of an unmitigated rate of climate change on key Earth system components, ecological systems, and human society over the next 50 years are likely to be severe and possibly irreversible on century time scales.


1. Earth and Societal Systems Research

Successfully addressing the challenges of global, regional, and local climate change requires enhanced understanding of Earth system dynamics at many scales. Climate change is a very complex phenomenon involving the coupled physical, chemical, and biological processes affecting the atmosphere, land and fresh water surfaces, and the oceans. (NRC, 2010a) The United States has been a leader in Earth system and climate change research, and, after a reduction in support at mid-decade, federal funding has recently increased. This enhanced research funding is required to support increased activities addressing a range of vital topics, including atmospheric chemistry, dynamics and radiative transport; cloud and aerosol chemistry and physics; ocean biogeochemistry and dynamics; glacial, ice cap and sea ice dynamics; hydrology; terrestrial and ocean ecology; soil microbiology; multi-scale Earth system modeling and other key disciplines. The ability to quantify trends in climate parameters and resulting impacts on geological and ecological systems at relevant scales will require the enhancement and maintenance of sophisticated Earth observation satellites as well as comprehensive in situ atmospheric, oceanic, and ecological sensor systems. Earth systems research must thoroughly investigate the rate, extent, and consequences of changing ocean acidity (NRC, 2010e) and to evaluate the effectiveness and consequences of geoengineering schemes to manipulate solar radiation reaching the Earth’s surface and to remove and sequester greenhouse gases from emissions streams or the ambient atmosphere.

However, the research challenge is not only to develop a more comprehensive understanding of the Earth systems that create and respond to climate, but to develop the scientific understanding necessary for society to develop, evaluate, and wisely adopt strategies capable of mitigating drastic climate change and to adapt to the inevitable climate changes that are already occurring and will evolve before successful mitigation strategies can be effective. Thus, “climate research needs to be integrative and interdisciplinary,” encompassing many societal components and activities that are profoundly influenced by climate, including fresh water resources, agriculture; fisheries and food production, public health, transportation, the built environment, energy production and use, and economic well-being. (NRC, 2010a)

Recommendation 1a

Maintain robust and uninterrupted federal funding for a comprehensive U.S. Earth systems research program to better define and document current and predict future impacts of climate change on local, regional, national and global scales. Cooperation and collaboration with other nations on both a wide-ranging Earth systems research agenda and the maintenance and enhancement of necessary Earth observing systems that detect and track key climate parameters should be emphasized.

Recommendation 1b

Expand the current U.S. climate research program to more fully investigate the interactions of Earth systems with vital societal systems’ components and activities. The aim is to better inform the systematic analyses required to develop and evaluate potential climate change mitigation and adaptation strategies and to measure the effectiveness and consequences of implemented policies.

2. Greenhouse Gas Emission Reduction

It is unquestioned that greenhouse gas emissions and levels have been increasing over the past 150 years, as fossil fuels have become the dominant fuels worldwide. Although we cannot precisely predict the effects on the earth’s climate, scientific consensus expects increased global temperatures resulting in adverse consequences throughout much of the world. Even in the face of uncertainty, the most prudent action by the United States and other nations is to minimize greenhouse gas emissions using current technologies to avert the most severe projected effects of climate change while also gaining the benefits of reduced fossil fuel combustion (NRC, 2010b).

Transportation and electricity generation account for almost three quarters of the carbon dioxide generated in the United States and thus should be a focus for reducing emissions. Opportunities to reduce carbon dioxide emissions in the transportation sector include enhanced fuel economy for on- and off-road vehicles and more convenient and available mass transit. Adopting non-combustion energy sources based on solar thermal, solar photovoltaic, wind, tidal power, or nuclear energy can reduce carbon dioxide emissions produced by fossil fuel combustion for electricity generation. Nuclear generation of electrical power is already technologically mature, but issues of fuel diversion prevention, spent fuel disposal, and power plant security hinder the expansion of this technology. Conservation of energy can be accomplished through better insulated, more efficiently heated and cooled buildings and more efficient lighting—often at reduced life cycle cost. However, a complete life cycle analysis of the greenhouse gas emissions and other environmental impacts—as well as the potential costs, savings, and safety concerns of each alternative energy source—must be objectively evaluated before large-scale adoption.

Fossil-fueled electrical power generation systems may also be part of carbon dioxide reduction strategies if effective and economic means to sequester carbon dioxide emissions from coal combustion or advanced coal processing are developed. Successful efforts to reduce petroleum and natural gas consumption through conservation or sustainable-fuel substitution will not only reduce net carbon dioxide emissions, but also reduce reliance on fuel sources that are increasingly insecure for both economic and geopolitical reasons. Reduced reliance on traditional combustion-driven energy systems will also contribute to both better air quality and reduced acidification of the ocean. Many opportunities also exist to reduce non-carbon dioxide greenhouse emissions—including biogenic methane from landfills, agriculture, and other land-use practices—and biogenic nitrous oxide from agricultural and non-agricultural fertilizer use, air pollutant deposition, and waste disposal. Enhanced research in the fields of energy efficiency and conservation, alternative and renewable energy sources, climate change adaptation, pollution prevention, and carbon sequestration will also support other important national goals: energy security, economic prosperity, and environmental protection.

Recommendation 2a

The United States should develop a portfolio of subsidies, tax, regulatory, and other incentives to reduce greenhouse gas emissions and allow advanced energy technologies, as they mature, to operate on an even playing field with current energy sources. "A carbon pricing strategy is a critical foundation of the policy portfolio for limiting future climate change. It creates incentives for cost-effective reduction of GHGs and provides the basis for innovation and a sustainable market for renewable resources" (NRC, 2010b). This carbon-pricing strategy should take into consideration the full life-cycle costs and sustainability implications of the carbon effects from various energy options. The United States should also work closely with all major greenhouse-gas emitter nations to secure their commitment to similar greenhouse-gas emission reductions.

Recommendation 2b

The United States should significantly raise its public and private sector investments in technologies to mitigate climate change through economically viable energy conservation, sustainable fuel substitution for fossil fuels, carbon sequestration, and non-fossil fuel based energy sources with significantly reduced life cycle impacts on the environment. The following key actions should be included:

Encouragement to share best practices for business and industry using private sector funding for development of enhanced low-emission, energy technologies and energy-efficient processes—especially since many of these are cost effective. Encouragement of additional venture funding to commercialize new energy-efficient technologies. The growing international demand for advanced, sustainable energy and energy-efficient process technologies in both developed and developing countries represents a major market that U.S. based companies should make every effort to serve, reaping economic benefits for themselves and environmental benefits for everyone.

Comprehensive evaluation of the life cycle environmental, health, safety, economic and social impacts of new and existing technologies and processes before and during new technology implementation to ensure they help solve climate change issues without creating unanticipated problems.

Enhanced federal R&D funding to develop both innovative energy sources with low net greenhouse gas emission and energy-efficient technologies and processes for the industrial, agricultural and transportation sectors.

Federal government revaluation of subsidies and tax, regulatory and other incentives to allow advanced energy technologies, as they mature, to operate on an even playing field with current energy sources.

3. Adaptation to Global Change

The current levels of long-lived atmospheric greenhouse gases and the levels of increased CO2 and heat absorbed by the world’s oceans ensure that the climate will almost certainly continue to increase for decades, even if greenhouse gas and absorbing particle emissions are scaled back to more sustainable levels (IPCC, 2007; NRC, 2010a; 2010c). Thus, our nation and the world must be prepared to adapt to changes in water supplies, agricultural productivity, severe weather patterns, sea-level rise, ocean acidification and ecosystem viabilities.

The enhanced research and development activities called for in Recommendations 1a and 1b, above, will help us better predict the circumstances to which we must adapt. Additional research will be needed to understand how to enable society to survive and thrive under new climate conditions. In cooperation with local, state and regional government, community, business, environmental and academic leaders the federal government will need to develop a collaborative national climate change adaptation strategy (NRC, 2010d). The White House Council on Environmental Quality (CEQ) has issued a progress report on the progress of a federal interagency task force charged to recommend actions to support a national climate change adaptation strategy (CEQ, 2010).

Recommendation 3a

Collaboration at every level of government and with other nations should be encouraged to assess current and probable future climate change impacts at local, state, regional, national and global scales and to share ways to successfully cope with climate change effects.

Recommendation 3b

Local, state, and regional entities should identify relevant climate change threats and develop and evaluate appropriate adaptation strategies that meet the needs of their communities. The federal government, working collaboratively with local, state, and regional governments and appropriate stakeholders, should integrate these adaptation strategies into a national climate change adaptation strategy.

4. Climate Change Literacy and Education

As described above, climate science is highly complex, requiring a multi-temporal and multi-spatial understanding of the interrelationships of intricate chemical, physical, and biological systems. Evaluating policy alternatives requires an understanding of engineering trade-offs associated with risk, life-cycle, and cost-benefit analyses. Decisions involve many factors beyond climate science, including economics, social values, competing priorities, and the risk of uncertainty. Climate change education requires a risk-management approach that integrates diverse and complicated disciplines to account for the inherent uncertainties about the timing, likelihood, and severity of the impacts, as well as the human dimensions that greatly influence making decisions. As described by the Climate Literacy Guide (USGRP, 2009), a climate-literate person

understands the essential principles of Earth's climate system,

knows how to assess scientifically credible information about climate,

communicates about climate and climate change in a meaningful way, and

is able to make informed and responsible decisions with regard to actions that may affect climate.

To make informed decisions, people need a basic understanding of the causes, likelihood, and severity of the impacts of climate change, and the range, cost, and efficacy of different options to limit or adapt. Transparency, accountability, and fairness in the measurement, reporting, and verification of data on climate change risks and vulnerabilities, sources of GHG emissions, and climate policy are priorities. Climate educators and communicators at all levels of society should set a tone of respect for diverse perspectives and an open and honest consideration of the implications of various responses to climate change. When discussion moves from core scientific concepts to more complex issues involving societal values, students should learn how to engage in responsible, respectful discourse and debate, as well as critical thinking and analysis skills (NRC, 2010d).

Climate change education for the public is essential to informed rational personal choices. Informal science education can play a critical role in reaching broad and diverse audiences and is well situated to help improve public climate change awareness, understanding, and informed decision-making.

As thought leaders in their communities, public institutions such as schools, museums, and universities must take a lead role in demonstrating sustainable technologies and reducing their own emissions footprint. In an era of decreasing financial resources, such investment can also pay significant dividends in reducing the cost of education. Properly implemented, these initiatives provide living laboratories for students, teachers, parents, and the broader public to explore, learn, and understand what sustainability means and how this relates to reducing the risk of climate change.

Recommendation 4a

Develop a national strategy to support climate change education and communication that both involves students, technical professionals, public servants and the general public, as well as being integrated with state and local initiatives. A national climate education act could serve as a catalyzing agent to reinvigorate science, technology, engineering, and mathematics (STEM) education across the nation. Such a strategy should include an integrated approach to sustainability education that connects science with social science, risk management, and economic issues. Such a policy must also include integrated support for informal science education.

Recommendation 4b

Provide federal support to facilitate the implementation of green and sustainable technologies that transform our educational environment. Specific supported activities should include efforts to recover or retain green space, retrofit programs to enhance energy efficiency or encourage the use of sustainable energy technologies, conservation of water resources, the use of renewable resources, and other efforts that reduce greenhouse gas emissions (including emissions from electrical power generation, heating, commuting, and air travel).



1. CEQ, 2010, Progress Report of the Interagency Climate Change Adaptation Task Force: Recommended Actions in Support of a National Climate Change Adaptation Strategy

2. Daily, G.C., et al., 2000, The Value of Nature and the Nature of Value, Science 289, 395-396.

3. IAC, 2010, Climate Change Assessments, Review of the Processes & Procedures of the IPCC, InterAcademy Council]

4. IPCC, 2007, Intergovernmental Panel on Climate Change

5. NRC, 2010a, Advancing the Science of Climate Change, National Research Council, National Academies Press, Washington, D.C.

6. NRC, 2010b, Limiting the Magnitude of Climate Change, National Research Council, National Academies Press, Washington, D.C.

7. NRC, 2010c, Adapting to the Impacts of Climate Change, National Research Council, National Academies Press, Washington, D.C.

8. NRC, 2010d, Informing an Effective Response to Climate Change, National Research Council, National Academies Press, Washington, D.C.

9. NRC, 2010e, Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean, National Research Council, National Academies Press, Washington, D.C.

10. USGRP, 2009, Climate Literacy Guide, US Global Change Research Program]
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Postby admin » Thu Jun 18, 2015 5:43 am


5. Human-Induced Climate Change Requires Urgent Action (2013)

Humanity is the major influence on the global climate change observed over the past 50 years. Rapid societal responses can significantly lessen negative outcomes.

Human activities are changing Earth's climate. At the global level, atmospheric concentrations of carbon dioxide and other heat‐trapping greenhouse gases have increased sharply since the Industrial Revolution. Fossil fuel burning dominates this increase. Human‐caused increases in greenhouse gases are responsible for most of the observed global average surface warming of roughly 0.8°C (1.5°F) over the past 140 years. Because natural processes cannot quickly remove some of these gases (notably carbon dioxide) from the atmosphere, our past, present, and future emissions will influence the climate system for millennia.

Extensive, independent observations confirm the reality of global warming. These observations show large-scale increases in air and sea temperatures, sea level, and atmospheric water vapor; they document decreases in the extent of mountain glaciers, snow cover, permafrost, and Arctic sea ice. These changes are broadly consistent with long-understood physics and predictions of how the climate system is expected to respond to human‐caused increases in greenhouse gases. The changes are inconsistent with explanations of climate change that rely on known natural influences.

Climate models predict that global temperatures will continue to rise, with the amount of warming primarily determined by the level of emissions. Higher emissions of greenhouse gases will lead to larger warming, and greater risks to society and ecosystems. Some additional warming is unavoidable due to past emissions.

Climate change is not expected to be uniform over space or time. Deforestation, urbanization, and particulate pollution can have complex geographical, seasonal, and longer-term effects on temperature, precipitation, and cloud properties. In addition, human-induced climate change may alter atmospheric circulation, dislocating historical patterns of natural variability and storminess.

In the current climate, weather experienced at a given location or region varies from year to year; in a changing climate, both the nature of that variability and the basic patterns of weather experienced can change, sometimes in counterintuitive ways -- some areas may experience cooling, for instance. This raises no challenge to the reality of human-induced climate change.

Impacts harmful to society, including increased extremes of heat, precipitation, and coastal high water are currently being experienced, and are projected to increase. Other projected outcomes involve threats to public health, water availability, agricultural productivity (particularly in low-latitude developing countries), and coastal infrastructure, though some benefits may be seen at some times and places. Biodiversity loss is expected to accelerate due to both climate change and acidification of the oceans, which is a direct result of increasing carbon dioxide levels.

While important scientific uncertainties remain as to which particular impacts will be experienced where, no uncertainties are known that could make the impacts of climate change inconsequential. Furthermore, surprise outcomes, such as the unexpectedly rapid loss of Arctic summer sea ice, may entail even more dramatic changes than anticipated.

Actions that could diminish the threats posed by climate change to society and ecosystems include substantial emissions cuts to reduce the magnitude of climate change, as well as preparing for changes that are now unavoidable. The community of scientists has responsibilities to improve overall understanding of climate change and its impacts. Improvements will come from pursuing the research needed to understand climate change, working with stakeholders to identify relevant information, and conveying understanding clearly and accurately, both to decision makers and to the general public.

Adopted by the American Geophysical Union December 2003; Revised and Reaffirmed December 2007, February 2012, August 2013.

6. Global Climate Change and Human Health (2013)

H-135.938 Global Climate Change and Human Health

Our AMA:

1. Supports the findings of the Intergovernmental Panel on Climate Change’s fourth assessment report and concurs with the scientific consensus that the Earth is undergoing adverse global climate change and that anthropogenic contributions are significant. These climate changes will create conditions that affect public health, with disproportionate impacts on vulnerable populations, including children, the elderly, and the poor.

2. Supports educating the medical community on the potential adverse public health effects of global climate change and incorporating the health implications of climate change into the spectrum of medical education, including topics such as population displacement, heat waves and drought, flooding, infectious and vector-borne diseases, and potable water supplies.

3. (a) Recognizes the importance of physician involvement in policymaking at the state, national, and global level and supports efforts to search for novel, comprehensive, and economically sensitive approaches to mitigating climate change to protect the health of the public; and (b) recognizes that whatever the etiology of global climate change, policymakers should work to reduce human contributions to such changes.

4. Encourages physicians to assist in educating patients and the public on environmentally sustainable practices, and to serve as role models for promoting environmental sustainability.

5. Encourages physicians to work with local and state health departments to strengthen the public health infrastructure to ensure that the global health effects of climate change can be anticipated and responded to more efficiently, and that the AMA’s Center for Public Health Preparedness and Disaster Response assist in this effort.

6. Supports epidemiological, translational, clinical and basic science research necessary for evidence-based global climate change policy decisions related to health care and treatment. (CSAPH Rep. 3, I-08; Reaffirmation A-14)

7. Climate Change: An Information Statement of the American Meteorological Society (2012)

Climate Change

An Information Statement of the American Meteorological Society

(Adopted by AMS Council 20 August 2012)

The following is an AMS Information Statement intended to provide a trustworthy, objective, and scientifically up-to-date explanation of scientific issues of concern to the public at large.


This statement provides a brief overview of how and why global climate has changed over the past century and will continue to change in the future. It is based on the peer-reviewed scientific literature and is consistent with the vast weight of current scientific understanding as expressed in assessments and reports from the Intergovernmental Panel on Climate Change, the U.S. National Academy of Sciences, and the U.S. Global Change Research Program. Although the statement has been drafted in the context of concerns in the United States, the underlying issues are inherently global in nature.

How is climate changing?

Warming of the climate system now is unequivocal, according to many different kinds of evidence. Observations show increases in globally averaged air and ocean temperatures, as well as widespread melting of snow and ice and rising globally averaged sea level. Surface temperature data for Earth as a whole, including readings over both land and ocean, show an increase of about 0.8°C (1.4°F) over the period 1901–2010 and about 0.5°C (0.9°F) over the period 1979–2010 (the era for which satellite-based temperature data are routinely available). Due to natural variability, not every year is warmer than the preceding year globally. Nevertheless, all of the 10 warmest years in the global temperature records up to 2011 have occurred since 1997, with 2005 and 2010 being the warmest two years in more than a century of global records. The warming trend is greatest in northern high latitudes and over land. In the U.S., most of the observed warming has occurred in the West and in Alaska; for the nation as a whole, there have been twice as many record daily high temperatures as record daily low temperatures in the first decade of the 21st century.

The effects of this warming are especially evident in the planet's polar regions. Arctic sea ice extent and volume have been decreasing for the past several decades. Both the Greenland and Antarctic ice sheets have lost significant amounts of ice. Most of the world's glaciers are in retreat.

Other changes, globally and in the U.S., are also occurring at the same time. The amount of rain falling in very heavy precipitation events (the heaviest 1% of all precipitation events) has increased over the last 50 years throughout the U.S. Freezing levels are rising in elevation, with rain occurring more frequently instead of snow at mid-elevations of western mountains. Spring maximum snowpack is decreasing, snowmelt occurs earlier, and the spring runoff that supplies over two-thirds of western U.S. streamflow is reduced. Evidence for warming is also observed in seasonal changes across many areas, including earlier springs, longer frost-free periods, longer growing seasons, and shifts in natural habitats and in migratory patterns of birds and insects.

Globally averaged sea level has risen by about 17 cm (7 inches) in the 20th century, with the rise accelerating since the early 1990s. Close to half of the sea level rise observed since the 1970s has been caused by water expansion due to increases in ocean temperatures. Sea level is also rising due to melting from continental glaciers and from ice sheets on both Greenland and Antarctica. Locally, sea level changes can depend also on other factors such as slowly rising or falling land, which results in some local sea level changes much larger or smaller than the global average. Even small rises in sea level in coastal zones are expected to lead to potentially severe impacts, especially in small island nations and in other regions that experience storm surges associated with vigorous weather systems.

Why is climate changing?

Climate is always changing. However, many of the observed changes noted above are beyond what can be explained by the natural variability of the climate. It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide. The most important of these over the long term is CO2, whose concentration in the atmosphere is rising principally as a result of fossil-fuel combustion and deforestation. While large amounts of CO2 enter and leave the atmosphere through natural processes, these human activities are increasing the total amount in the air and the oceans. Approximately half of the CO2 put into the atmosphere through human activity in the past 250 years has been taken up by the ocean and terrestrial biosphere, with the other half remaining in the atmosphere. Since long-term measurements began in the 1950s, the atmospheric CO2 concentration has been increasing at a rate much faster than at any time in the last 800,000 years. Having been introduced into the atmosphere it will take a thousand years for the majority of the added atmospheric CO2 to be removed by natural processes, and some will remain for thousands of subsequent years.

Water vapor also is an important atmospheric greenhouse gas. Unlike other greenhouse gases, however, the concentration of water vapor depends on atmospheric temperature and is controlled by the global climate system through its hydrological cycle of evaporation- condensation-precipitation. Water vapor is highly variable in space and time with a short lifetime, because of weather variability. Observations indicate an increase in globally averaged water vapor in the atmosphere in recent decades, at a rate consistent with the response produced by climate models that simulate human-induced increases in greenhouse gases. This increase in water vapor also strengthens the greenhouse effect, amplifying the impact of human-induced increases in other greenhouse gases.

Human activity also affects climate through changes in the number and physical properties of tiny solid particles and liquid droplets in the atmosphere, known collectively as atmospheric aerosols. Examples of aerosols include dust, sea salt, and sulfates from air pollution. Aerosols have a variety of climate effects. They absorb and redirect solar energy from the sun and thermal energy emitted by Earth, emit energy themselves, and modify the ability of clouds to reflect sunlight and to produce precipitation. Aerosols can both strengthen and weaken greenhouse warming, depending on their characteristics. Most aerosols originating from human activity act to cool the planet and so partly counteract greenhouse gas warming effects. Aerosols lofted into the stratosphere [between about 13 km (8 miles) and 50 km (30 miles) altitude above the surface] by occasional large sulfur-rich volcanic eruptions can reduce global surface temperature for several years. By contrast, carbon soot from incomplete combustion of fossil fuels warms the planet, so that decreases in soot would reduce warming. Aerosols have lifetimes in the troposphere [at altitudes up to approximately 13 km (8 miles) from the surface in the middle latitudes] on the order of one week, much shorter than that of most greenhouse gases, and their prevalence and properties can vary widely by region.

Land surface changes can also affect the surface exchanges of water and energy with the atmosphere. Humans alter land surface characteristics by carrying out irrigation, removing and introducing forests, changing vegetative land cover through agriculture, and building cities and reservoirs. These changes can have significant effects on local-to- regional climate patterns, which adds up to a small impact on the global energy balance as well.

How can climate change be projected into the future?

Factors that have altered climate throughout history, both human (such as human emission of greenhouse gases) and natural (such as variation of the Sun's energy emission, the Earth's orbit about the Sun, and volcanic eruptions), will continue to alter climate in the future. Climate projections for decades into the future are made using complex numerical models of the climate system that account for changes in the flow of energy into and out of the Earth system on time scales much longer than the predictability limit (of about two weeks) for individual weather systems. The difference between weather and climate is critically important in considering predictability. Climate is potentially predictable for much longer time scales than weather for several reasons. One reason is that climate can be meaningfully characterized by seasonal-to-decadal averages and other statistical measures, and the averaged weather is more predictable than individual weather events. A helpful analogy in this regard is that population averages of human mortality are predictable while life spans of individuals are not. A second reason is that climate involves physical systems and processes with long time scales, including the oceans and snow and ice, while weather largely involves atmospheric phenomena (e.g., thunderstorms, intense snow storms) with short time scales. A third reason is that climate can be affected by slowly changing factors such as human- induced changes in the chemical composition of the atmosphere, which alter the natural greenhouse effect.

Climate models simulate the important aspects of climate and climate change based on fundamental physical laws of motion, thermodynamics, and radiative transfer. These models report on how climate would change in response to several specific “scenarios” for future greenhouse gas emission possibilities. Future climate change projections have uncertainties that occur for several reasons — because of differences among models, because long-term predictions of natural variations (e.g., volcanic eruptions and El Niño events) are not possible, and because it is not known exactly how greenhouse gas emissions will evolve in future decades. Future emissions will depend on global social and economic development, and on the extent and impact of activities designed to reduce greenhouse gas and black carbon emissions.

Changes in the means and extremes of temperature and precipitation in response to increasing greenhouse gases can be projected over decades to centuries into the future, even though the timing of individual weather events cannot be predicted on this time scale. Because it would take many years for observations to verify whether a future climate projection is correct, researchers establish confidence in these projections by using historical and paleoclimate evidence and through careful study of observations of the causal chain between energy flow changes and climate-pattern responses. A valuable demonstration of the validity of current climate models is that when they include all known natural and human-induced factors that influence the global atmosphere on a large scale, the models reproduce many important aspects of observed changes of the 20th-century climate, including (1) global, continental, and subcontinental mean and extreme temperatures, (2) Arctic sea ice extent, (3) the latitudinal distribution of precipitation, and (4) extreme precipitation frequency.

Model limitations include inadequate representations of some important processes and details. For example, a typical climate model does not yet treat fully the complex dynamical, radiative, and microphysical processes involved in the evolution of a cloud or the spatially variable nature of soil moisture, or the atmospheric interactions with the biosphere. Nevertheless, in spite of these limitations, climate models have demonstrated skill in reproducing past climates, and they agree on the broad direction of future climate.

How is the climate expected to change in the future?

Future warming of the climate is inevitable for many years due to the greenhouse gases already added to the atmosphere and the heat that has been taken up by the oceans. Amelioration might be possible through devising and implementing environmentally responsible geoengineering approaches, such as capture and storage measures to remove CO2 from the atmosphere. However, the potential risks of geoengineering may be quite large, and more study of the topic (including other environmental consequences) is needed. The subject of geoengineering is outside the scope of this statement (for more information see AMS Statement on Geoengineering).

In general, many of the climate-system trends observed in recent decades are projected to continue. Those projections, and others in this section, are largely based on simulations conducted with climate models, and assume that the amount of greenhouse gas in the atmosphere will continue to increase due to human activity. Global efforts to slow greenhouse gas emissions have been unsuccessful so far. However, were future technologies and policies able to achieve a rapid reduction of greenhouse gas emissions — an approach termed “mitigation” — this would greatly lessen future global warming and its impacts.

Confidence in the projections is higher for temperature than for other climate elements such as precipitation, and higher at the global and continental scales than for the regional and local scales. The model projections show that the largest warming will occur in northern polar regions, over land areas, and in the winter season, consistent with observed trends.

In the 21st century, global sea level also will continue to rise although the rise will not be uniform at all locations. With its large mass and high capacity for heat storage, the ocean will continue to slowly warm and thus thermally expand for several centuries. Model simulations project about 27 cm (10 inches) to 71 cm (28 inches) of global sea level rise due to thermal expansion and melting of ice in the 21st century. Moreover, paleoclimatic observations and ice-sheet modeling indicate that melting of the Greenland and the West Antarctic ice sheets will eventually cause global sea level to rise several additional meters by 2500 if warming continues at its present rate beyond the 21st century.

Atmospheric water content will increase globally, consistent with warmer temperatures, and consequently the global hydrological cycle will continue to accelerate. For many areas, model simulations suggest there will be a tendency towards more intense rain and snow events separated by longer periods without precipitation. However, changes in precipitation patterns are expected to differ considerably by region and by season. In some regions, the accelerated hydrological cycle will likely reinforce existing patterns of precipitation, leading to more severe droughts and floods. Further poleward, the greater warming at high latitudes and over land likely will change the large-scale atmospheric circulation, leading to significant regional shifts in precipitation patterns. For example, the model simulations suggest that precipitation will increase in the far northern parts of North America, and decrease in the southwest and south-central United States where more droughts will occur.

Climate-model simulations further project that heavy precipitation events will continue to become more intense and frequent, leading to increased precipitation totals from the strongest storms. This projection has important implications for water-resource management and flood control. The simulations also indicate the likelihood of longer dry spells between precipitation events in the subtropics and lower-middle latitudes, with shorter dry spells projected for higher latitudes where mean precipitation is expected to increase. Continued warming also implies a reduction of winter snow accumulations in favor of rain in many places, and thus a reduced spring snowpack. Rivers now fed by snowmelt will experience earlier spring peaks and reduced warm-season flows. Widespread retreat of mountain glaciers is expected to eventually lead to reduced dry season flows for glacier-fed rivers. Drought is projected to increase over Africa, Europe, and much of the North American continental interior, and particularly the southwest United States. However, natural variations in world ocean conditions at decadal scale, such as those in the North Pacific and North Atlantic basins, could offset or enhance such changes in the next few decades. For the longer term, paleoclimatic observations suggest that droughts lasting decades are possible and that these prolonged droughts could occur with little warning.

Weather patterns will continue to vary from day to day and from season to season, but the frequency of particular patterns and extreme weather and climate events may change as a result of global warming. Model simulations project an increased proportion of global hurricanes that are in the strongest categories, namely 4 and 5 on the Saffir-Simpson scale, although the total counts of hurricanes may not change or may even decrease. Some regional variations in these trends are possible. Simulations also indicate that midlatitude storm tracks will shift poleward. Interannual variations of important large-scale climate conditions (such as El Niño and La Niña) will also continue to occur, but there may be changes in their intensity, frequency, and other characteristics, resulting in different responses by the atmosphere. Heat waves and cold snaps and their associated weather conditions will continue to occur, but proportionately more extreme warm periods and fewer cold periods are expected. Indeed, what many people traditionally consider a cold wave is already changing toward less severe conditions. Frost days (those with minimum temperature below freezing) will be fewer and growing seasons longer. Drier conditions in summer, such as those anticipated for the southern United States and southern Europe, are expected to contribute to more severe episodes of extreme heat. Critical thresholds of daily maximum temperature, above which ecosystems and crop systems (e.g., food crops such as rice, corn, and wheat) suffer increasingly severe damage, are likely to be exceeded more frequently.

The Earth system is highly interconnected and complex, with many processes and feedbacks that only slowly are becoming understood. In particular, the carbon cycle remains a large source of uncertainty for the projection of future climate. It is unclear if the land biosphere and oceans will be able to continue taking up carbon at their current rate into the future. One unknown is whether soil and vegetation will become a global source rather than a sink of carbon as the planet warms. Another unknown is the amount of methane that will be released due to high-latitude warming. There are indications that large regions of the permafrost in parts of Alaska and other northern polar areas are already thawing, with the potential to release massive amounts of carbon into the atmosphere beyond those being directly added by human activity. The portion of the increased CO2 release that is absorbed by the world ocean is making the ocean more acidic, with negative implications for shell- and skeleton-forming organisms and more generally for ocean ecosystems. These processes are only now being quantified by observation and introduced into climate models, and more research is required to fully understand their potential impacts. As impacts of climate change are of regional and local nature, more research is also required to improve climate projections at local and regional scales, and for weather and climate extremes in particular.

Final remarks

There is unequivocal evidence that Earth's lower atmosphere, ocean, and land surface are warming; sea level is rising; and snow cover, mountain glaciers, and Arctic sea ice are shrinking. The dominant cause of the warming since the 1950s is human activities. This scientific finding is based on a large and persuasive body of research. The observed warming will be irreversible for many years into the future, and even larger temperature increases will occur as greenhouse gases continue to accumulate in the atmosphere. Avoiding this future warming will require a large and rapid reduction in global greenhouse gas emissions. The ongoing warming will increase risks and stresses to human societies, economies, ecosystems, and wildlife through the 21st century and beyond, making it imperative that society respond to a changing climate. To inform decisions on adaptation and mitigation, it is critical that we improve our understanding of the global climate system and our ability to project future climate through continued and improved monitoring and research. This is especially true for smaller (seasonal and regional) scales and weather and climate extremes, and for important hydroclimatic variables such as precipitation and water availability.

Technological, economic, and policy choices in the near future will determine the extent of future impacts of climate change. Science-based decisions are seldom made in a context of absolute certainty. National and international policy discussions should include consideration of the best ways to both adapt to and mitigate climate change. Mitigation will reduce the amount of future climate change and the risk of impacts that are potentially large and dangerous. At the same time, some continued climate change is inevitable, and policy responses should include adaptation to climate change. Prudence dictates extreme care in accounting for our relationship with the only planet known to be capable of sustaining human life.

[This statement is considered in force until August 2017 unless superseded by a new statement issued by the AMS Council before this date.]

© American Meteorological Society, 45 Beacon Street, Boston, MA 02108-3693

8. APS National Policy 07.1 Climate Change (2007)

National Policy


(Adopted by Council on November 18, 2007)

Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth's climate. Greenhouse gases include carbon dioxide as well as methane, nitrous oxide and other gases. They are emitted from fossil fuel combustion and a range of industrial and agricultural processes.

The evidence is incontrovertible: Global warming is occurring.

If no mitigating actions are taken, significant disruptions in the Earth’s physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now.

Because the complexity of the climate makes accurate prediction difficult, the APS urges an enhanced effort to understand the effects of human activity on the Earth’s climate, and to provide the technological options for meeting the climate challenge in the near and longer terms. The APS also urges governments, universities, national laboratories and its membership to support policies and actions that will reduce the emission of greenhouse gases.

Climate Change Commentary

(adopted by Council on April 18, 2010)

There is a substantial body of peer reviewed scientific research to support the technical aspects of the 2007 APS statement. The purpose of the following commentary is to provide clarification and additional details.

The first sentence of the APS statement is broadly supported by observational data, physical principles, and global climate models. Greenhouse gas emissions are changing the Earth's energy balance on a planetary scale in ways that affect the climate over long periods of time (~100 years). Historical records indicate that the Earth’s climate is sensitive to energy changes, both external (the sun’s radiative output, changes in Earth’s orbit, etc.) and internal. Internal to our global system, it is not just the atmosphere, but also the oceans and land that are involved in the complex dynamics that result in global climate. Aerosols and particulates resulting from human and natural sources also play roles that can either offset or reinforce greenhouse gas effects. While there are factors driving the natural variability of climate (e.g., volcanoes, solar variability, oceanic oscillations), no known natural mechanisms have been proposed that explain all of the observed warming in the past century. Warming is observed in land-surface temperatures, sea-surface temperatures, and for the last 30 years, lower-atmosphere temperatures measured by satellite. The second sentence is a definition that should explicitly include water vapor. The third sentence notes various examples of human contributions to greenhouses gases. There are, of course, natural sources as well.

The evidence for global temperature rise over the last century is compelling. However, the word "incontrovertible" in the first sentence of the second paragraph of the 2007 APS statement is rarely used in science because by its very nature science questions prevailing ideas. The observational data indicate a global surface warming of 0.74 °C (+/- 0.18 °C) since the late 19th century. (Source:

The first sentence in the third paragraph states that without mitigating actions significant disruptions in the Earth's physical and ecological systems, social systems, security and health are likely. Such predicted disruptions are based on direct measurements (e.g., ocean acidification, rising sea levels, etc.), on the study of past climate change phenomena, and on climate models. Climate models calculate the effects of natural and anthropogenic changes on the ecosphere, such as doubling of the CO2-equivalent [1] concentration relative to its pre-industrial value by the year 2100. These models have uncertainties associated with radiative response functions, especially clouds and water vapor. However, the models show that water vapor has a net positive feedback effect (in addition to CO2 and other gases) on global temperatures. The impact of clouds is less certain because of their dual role as scatterers of incoming solar radiation and as greenhouse contributors. The uncertainty in the net effect of human activity on climate is reflected in the broad distribution of the predicted magnitude of the consequence of doubling of the CO2-equivalent concentration. The uncertainty in the estimates from various climate models for doubling CO2-equivalent concentration is in the range of 1°C to 3°C with the probability distributions having long tails out to much larger temperature changes.

The second sentence in the third paragraph articulates an immediate policy action to reduce greenhouse gas emissions to deal with the possible catastrophic outcomes that could accompany large global temperature increases. Even with the uncertainties in the models, it is increasingly difficult to rule out that non-negligible increases in global temperature are a consequence of rising anthropogenic CO2. Thus given the significant risks associated with global climate change, prudent steps should be taken to reduce greenhouse gas emissions now while continuing to improve the observational data and the model predictions.

The fourth paragraph, first sentence, recommends an enhanced effort to understand the effects of human activity on Earth's climate. This sentence should be interpreted broadly and more specifically: an enhanced effort is needed to understand both anthropogenic processes and the natural cycles that affect the Earth's climate. Improving the scientific understanding of all climate feedbacks is critical to reducing the uncertainty in modeling the consequences of doubling the CO2-equivalent concentration. In addition, more extensive and more accurate scientific measurements are needed to test the validity of climate models to increase confidence in their projections.

With regard to the last sentence of the APS statement, the role of physicists is not just " support policies and actions..." but also to participate actively in the research itself. Physicists can contribute in significant ways to understanding the physical processes underlying climate and to developing technological options for addressing and mitigating climate change.*



[1] The concentration of CO2 that would give the same amount of radiative impact as a given mixture of CO2 and other greenhouse gases (methane, nitrous oxide, etc.). The models sum the radiative effects of all trace gases and treat the total as if it comes from an "equivalent" CO2 concentration. The calculation for all gases other than CO2 takes into account only increments relative to their pre-industrial values, so that the pre-industrial effect for CO2 and CO2-equivalent are the same.

* In February 2012, per normal APS process, the Panel on Public Affairs recommended four minor copy edits so that the identification of sentences and paragraphs correspond to the 2007 APS Climate Change Statement above. View the copy edits.
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9. GSA Position Statement on Climate Change (2010)

Climate Change

Adopted in October 2006; revised April 2010; March 2013

Position Statement

Decades of scientific research have shown that climate can change from both natural and anthropogenic causes. The Geological Society of America (GSA) concurs with assessments by the National Academies of Science (2005), the National Research Council (2011), and the Intergovernmental Panel on Climate Change (IPCC, 2007) that global climate has warmed and that human activities (mainly greenhouse-gas emissions) account for most of the warming since the middle 1900s. If current trends continue, the projected increase in global temperature by the end of the twenty-first century will result in significant impacts on humans and other species. Addressing the challenges posed by climate change will require a combination of adaptation to the changes that are likely to occur and global reductions of CO2 emissions from anthropogenic sources.


This position statement (1) summarizes the strengthened basis for the conclusion that humans are a major factor responsible for recent global warming; (2) describes the significant effects on humans and ecosystems as greenhouse-gas concentrations and global climate reach projected levels; and (3) provides information for policy decisions guiding mitigation and adaptation strategies designed to address the future impacts of anthropogenic warming.


Scientific advances in the first decade of the 21st century have greatly reduced previous uncertainties about the amplitude and causes of recent global warming. Ground-station measurements have shown a warming trend of ~0.8 °C since the mid-1800s, a trend consistent with (1) retreat of northern hemisphere snow and Arctic sea ice in the last 40 years; (2) greater heat storage in the ocean over the last 50 years; (3) retreat of most mountain glaciers since 1850; (4) an ongoing rise of global sea level for more than a century; and (5) proxy reconstructions of temperature change over past centuries from archives including ice cores, tree rings, lake sediments, boreholes, cave deposits and corals. Both instrumental records and proxy indices from geologic sources show that global mean surface temperature was higher during the last few decades of the 20th century and the first decade of the 21st than during any comparable period during the preceding four centuries (National Research Council, 2006).

Measurements from satellites, which began in 1979, initially did not show a warming trend, but later studies (Mears and Wentz, 2005; Santer et al., 2008) found that the satellite data had not been fully adjusted for losses of satellite elevation through time, differences in time of arrival over a given location, and removal of higher-elevation effects on the lower tropospheric signal. With these factors taken into account, the satellite data are now in basic agreement with ground-station data and confirm a warming trend since 1979. In a related study, Sherwood et al. (2005) found problems with corrections of tropical daytime radiosonde measurements and largely resolved a previous discrepancy with ground-station trends. With instrumental discrepancies having been resolved, recent warming of Earth’s surface is now consistently supported by a wide range of measurements and proxies and is no longer open to serious challenge.

The geologic record contains unequivocal evidence of former climate change, including periods of greater warmth with limited polar ice, and colder intervals with more widespread glaciation. These and other changes were accompanied by major shifts in species and ecosystems. Paleoclimatic research has demonstrated that these major changes in climate and biota are associated with significant changes in climate forcing such as continental positions and topography, patterns of ocean circulation, the greenhouse gas composition of the atmosphere, and the distribution and amount of solar energy at the top of the atmosphere caused by changes in Earth's orbit and the evolution of the sun as a main sequence star. Cyclic changes in ice volume during glacial periods over the last three million years have been correlated to orbital cycles and changes in greenhouse gas concentrations, but may also reflect internal responses generated by large ice sheets. This rich history of Earth's climate has been used as one of several key sources of information for assessing the predictive capabilities of modern climate models. The testing of increasingly sophisticated climate models by comparison to geologic proxies is continuing, leading to refinement of hypotheses and improved understanding of the drivers of past and current climate change.

Given the knowledge gained from paleoclimatic studies, several long-term causes of the current warming trend can be eliminated. Changes in Earth’s tectonism and its orbit are far too slow to have played a significant role in a rapidly changing 150-year trend. At the other extreme, large volcanic eruptions have cooled global climate for a year or two, and El Niño episodes have warmed it for about a year, but neither factor dominates longer-term trends. Extensive efforts to find any other natural explanation of the recent trend have similarly failed.

As a result, greenhouse gas concentrations, which can be influenced by human activities, and solar fluctuations are the principal remaining factors that could have changed rapidly enough and lasted long enough to explain the observed changes in global temperature. Although the 3rd (2001) IPCC report allowed that solar fluctuations might have contributed as much as 30% of the warming since 1850, subsequent observations of Sun-like stars (Foukal et al., 2004) and new simulations of the evolution of solar sources of irradiance variations (Wang et al., 2005) have reduced these estimates. The 4th (2007) IPCC report concluded that changes in solar irradiance, continuously measured by satellites since 1979, account for less than 10% of the last 150 years of warming. Throughout the era of satellite observation, during periods of strong warming, the data show little evidence of increased solar influence (Foster and Rahmstorf, 2011; Lean and Rind, 2008).

Greenhouse gases remain as the major explanation for the warming. Observations and climate model assessments of the natural and anthropogenic factors responsible for this warming conclude that rising anthropogenic emissions of greenhouse gases have been an increasingly important contributor since the mid-1800s and the major factor since the mid-1900s (Meehl et al., 2004). The CO2 concentration in the atmosphere is now ~30% higher than peak levels that have been measured in ice cores spanning 800,000 years of age, and the methane concentration is 2.5 times higher. About half of Earth’s warming has occurred through the basic heat-trapping effect of the gases in the absence of any feedback processes. This “clear-sky” response to climate is known with high certainty. The other half of the estimated warming results from the net effect of feedbacks in the climate system: a large positive feedback from water vapor; a smaller positive feedback from snow and ice albedo; a negative feedback from aerosols, and still uncertain,feedbacks from clouds. The vertical structure of observed changes in temperature and water vapor in the troposphere is consistent with the anthropogenic greenhouse-gas “fingerprint” simulated by climate models (Santer et al., 2008). Considered in isolation, the greenhouse-gas increases during the last 150 years would have caused a warming larger than that actually measured, but negative feedback from aerosols and possibly clouds has offset part of the warming. In addition, because the oceans take decades to centuries to respond fully to climatic forcing, the climate system has yet to register the full effect of gas increases in recent decades.

These advances in scientific understanding of recent warming form the basis for projections of future changes. If greenhouse-gas emissions follow predicted trajectories, by 2100 atmospheric CO2 concentrations will reach two to four times pre-industrial levels, for a total warming of 2 °C to 4.5 °C compared to 1850. This range of changes in greenhouse gas concentrations and temperature would substantially alter the functioning of the planet in many ways. The projected changes involve risk to humans and other species: (1) continued shrinking of Arctic sea ice with effects on native cultures and ice-dependent biota; (2) less snow accumulation and earlier melt in mountains, with reductions in spring and summer runoff for agricultural and municipal water; (3) disappearance of mountain glaciers and their late-summer runoff; (4) increased evaporation from farmland soils and stress on crops; (5) greater soil erosion due to increases in heavy convective summer rainfall; (6) longer fire seasons and increases in fire frequency; (7) severe insect outbreaks in vulnerable forests; (8) acidification of the global ocean; and (9) fundamental changes in the composition, functioning, and biodiversity of many terrestrial and marine ecosystems. In addition, melting of Greenland and West Antarctic ice (still highly uncertain as to amount), along with thermal expansion of seawater and melting of mountain glaciers and small ice caps, will cause substantial future sea-level rise, affecting densely populated coastal regions, inundating farmland and dislocating large populations. Because large, abrupt climatic changes occurred within spans of just decades during previous ice-sheet fluctuations, the possibility exists for rapid future changes as ice sheets become vulnerable to large greenhouse-gas increases. Finally, carbon-climate model simulations indicate that 10–20% of the anthropogenic CO2 "pulse" could stay in the atmosphere for thousands of years, extending the duration of fossil-fuel warming and its effects on humans and other species. The acidification of the global ocean and its effects on ocean life are projected to last for tens of thousands of years.

Public Policy Aspects

Recent scientific investigations have strengthened the case for policy action to reduce greenhouse gas emissions and to adapt to unavoidable climate change. To strengthen the scientific contributions to policy discussions on how to address climate change, this statement from the Geological Society of America is intended to inform policymakers about improved knowledge of Earth's climate system based on advances in climate science. Recent scientific investigations have contributed to this improved understanding of the climate system and supplied strong evidence for human-induced global warming, providing policy makers with a unique perspective on which to base mitigation and adaptation strategies. Carefully researched and tested adaptation strategies can both reduce and limit negative impacts and explore potential positive impacts. Future climate change will pose societal, biological, economic, and strategic challenges that will require a combination of national and international emissions reductions and adaptations. These challenges will also require balanced and thoughtful national and international discussions leading to careful long-term planning and sustained policy actions.


There will be significant economic, health and safety impacts in the absence of global action on climate change. Public policy should include effective strategies for the reduction of greenhouse gas emissions. Cost-effective investments to improve the efficient use of Earth’s energy resources can reduce the economic impacts of future adaptation efforts. Strategies for reducing greenhouse-gas emissions should be evaluated based on their impacts on climate, on costs to global and national economies, and on positive and negative impacts on the health, safety and welfare of humans and ecosystems.

Comprehensive local, state, national and international planning is needed to address challenges posed by future climate change. Near-, mid-, and long-term strategies for mitigation of, and adaptation to climate change should be developed, based in part on knowledge gained from studies of previous environmental changes.

Public investment is needed to improve our understanding of how climate change affects society, including on local and regional scales, and to formulate adaptation measures. Sustained support of climate-related research to advance understanding of the past and present operation of the climate system is needed, with particular focus on the major remaining uncertainties in understanding and predicting Earth's future climate at regional and global scales. Research is needed to improve our ability to assess the response and resilience of natural and human systems to past, present, and future changes in the climate system.


To facilitate implementation of the goals of this position statement, the Geological Society of America recommends that its members take the following actions:

Actively participate in professional education and discussion activities to be technically informed about the latest advances in climate science. GSA should encourage symposia at regional, national and international meetings to inform members on mainstream understanding among geoscientists and climate scientists of the causes and future effects of global warming within the broader context of natural variability. These symposia should seek to actively engage members in hosted discussions that clarify issues, possibly utilizing educational formats other than the traditional presentation and Q&A session.

Engage in public education activities in the community, including the local level. Public education is a critical element of a proactive response to the challenges presented by global climate change. GSA members are encouraged to take an active part in outreach activities to educate the public at all levels (local, regional, national, and international) about the science of climate change and the importance of geological research in framing policy development. Such activities can include organizing and participating in community school activities; leading discussion groups in civic organizations; meeting with local and state community leaders and congressional staffs; participating in GSA's Congressional Visits Day; writing opinion pieces and letters to the editor for local and regional newspapers; contributing to online forums; and volunteering for organizations that support efforts to mitigate and adapt to global climate change.

Collaborate with a wide range of stakeholders and help educate and inform them about the causes and impacts of global climate change from the geosciences perspective. GSA members are encouraged to discuss with businesses and policy makers the science of climate change, as well as opportunities for transitioning from our predominant dependence on fossil fuels to greater use of low-carbon energies and energy efficiencies.

Work interactively with other science and policy societies to help inform the public and ensure that policymakers have access to scientifically reliable information. GSA should actively engage and collaborate with other earth-science organizations in recommending and formulating national and international strategies to address impending impacts of anthropogenic climate change.

Take advantage of the following list of references for a current scientific assessment of global climate change.



1. IPCC (Intergovernmental Panel on Climate Change), 2007, Summary for policymakers, in Climate Change 2007: The physical science basis: Cambridge, United Kingdom, Cambridge University Press, 18 p.

2. IPCC (Intergovernmental Panel on Climate Change), 2001, Summary for policymakers, in Climate Change 2001: Synthesis Report: Cambridge, United Kingdom, Cambridge University Press, 34 p.

3. National Academies of Science (2005). Joint academes statement: Global response to climate change. (

4. National Research Council (2011). America's Climate Choices. Washington, DC: The National Academies Press, 144 p.

Peer-Reviewed Articles

1. Foster, G. and Rahmstorf , S., 2011, Global temperature evolution 1979–2010, Environmental Research Letters, doi: 10.1088/1748-9326/6/4/044022.

2. Foukal, P.G., et al., 2004, A stellar view on solar variations and climate: Science, v. 306, p. 68–69.

3. Lean, J.L., and Rind, D.H., 2008, How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006, Geophysical Research Letters, doi: 10.1029/2008GL034864.

4. Mears, C.A., and Wentz, F.J., 2005, The effect of diurnal correction on satellite-derived lower tropospheric temperature: Science online, doi: 10.1126/science.1114772.

5. Meehl et al., 2004, Combinations of natural and anthropogenic forcings in twentieth-century climate: J. of Climate, v. 17, p. 3721-3727.

6. Santer, B., et al., 2008, Consistency of modeled and observed temperature trends in the tropical troposphere: International Journal of Climatology, v. 28, p. 1703–1722.

7. Sherwood, S., Lanzante, J., and Meyer, C., 2005, Radiosonde biases and late-20th century warming: Science online, doi: 10/1126/science.1115640.

8. Wang, Y.-M., Lean, J.L., and Sheeley, N.R. Jr., 2005, Modeling the Sun’s magnetic field and irradiance since 1713: Astrophysical Journal, v. 625, p. 522–538

10. Joint science academies' statement: Global response to climate change (2005)

Climate change is real

There will always be uncertainty in understanding a system as complex as the world's climate. However there is now strong evidence that significant global warming is occurring [1]. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. It is likely that most of the warming in recent decades can be attributed to human activities (IPCC 2001) [2]. This warming has already led to changes in the Earth's climate.

The existence of greenhouse gases in the atmosphere is vital to life on Earth – in their absence average temperatures would be about 30 centigrade degrees lower than they are today. But human activities are now causing atmospheric concentrations of greenhouse gases – including carbon dioxide, methane, tropospheric ozone, and nitrous oxide – to rise well above pre-industrial levels. Carbon dioxide levels have increased from 280 ppm in 1750 to over 375 ppm today – higher than any previous levels that can be reliably measured (i.e. in the last 420,000 years). Increasing greenhouse gases are causing temperatures to rise; the Earth's surface warmed by approximately 0.6 centigrade degrees over the twentieth century. The Intergovernmental Panel on Climate Change (IPCC) projected that the average global surface temperatures will continue to increase to between 1.4 centigrade degrees and 5.8 centigrade degrees above 1990 levels, by 2100.

Reduce the causes of climate change

The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action. It is vital that all nations identify cost-effective steps that they can take now, to contribute to substantial and long-term reduction in net global greenhouse gas emissions.

Action taken now to reduce significantly the build-up of greenhouse gases in the atmosphere will lessen the magnitude and rate of climate change. As the United Nations Framework Convention on Climate Change (UNFCCC) recognises, a lack of full scientific certainty about some aspects of climate change is not a reason for delaying an immediate response that will, at a reasonable cost, prevent dangerous anthropogenic interference with the climate system.

As nations and economies develop over the next 25 years, world primary energy demand is estimated to increase by almost 60%. Fossil fuels, which are responsible for the majority of carbon dioxide emissions produced by human activities, provide valuable resources for many nations and are projected to provide 85% of this demand (IEA 2004) [3]. Minimising the amount of this carbon dioxide reaching the atmosphere presents a huge challenge. There are many potentially cost- effective technological options that could contribute to stabilising greenhouse gas concentrations. These are at various stages of research and development. However barriers to their broad deployment still need to be overcome.

Carbon dioxide can remain in the atmosphere for many decades. Even with possible lowered emission rates we will be experiencing the impacts of climate change throughout the 21st century and beyond. Failure to implement significant reductions in net greenhouse gas emissions now, will make the job much harder in the future.

Prepare for the consequences of climate change

Major parts of the climate system respond slowly to changes in greenhouse gas concentrations. Even if greenhouse gas emissions were stabilised instantly at today's levels, the climate would still continue to change as it adapts to the increased emission of recent decades. Further changes in climate are therefore unavoidable. Nations must prepare for them.

The projected changes in climate will have both beneficial and adverse effects at the regional level, for example on water resources, agriculture, natural ecosystems and human health. The larger and faster the changes in climate, the more likely it is that adverse effects will dominate. Increasing temperatures are likely to increase the frequency and severity of weather events such as heat waves and heavy rainfall. Increasing temperatures could lead to large-scale effects such as melting of large ice sheets (with major impacts on low-lying regions throughout the world). The IPCC estimates that the combined effects of ice melting and sea water expansion from ocean warming are projected to cause the global mean sea-level to rise by between 0.1 and 0.9 metres between 1990 and 2100. In Bangladesh alone, a 0.5 metre sea-level rise would place about 6 million people at risk from flooding.

Developing nations that lack the infrastructure or resources to respond to the impacts of climate change will be particularly affected. It is clear that many of the world's poorest people are likely to suffer the most from climate change. Long-term global efforts to create a more healthy, prosperous and sustainable world may be severely hindered by changes in the climate.

The task of devising and implementing strategies to adapt to the consequences of climate change will require worldwide collaborative inputs from a wide range of experts, including physical and natural scientists, engineers, social scientists, medical scientists, those in the humanities, business leaders and economists.


We urge all nations, in the line with the UNFCCC principles [4], to take prompt action to reduce the causes of climate change, adapt to its impacts and ensure that the issue is included in all relevant national and international strategies. As national science academies, we commit to working with governments to help develop and implement the national and international response to the challenge of climate change.

G8 nations have been responsible for much of the past greenhouse gas emissions. As parties to the UNFCCC, G8 nations are committed to showing leadership in addressing climate change and assisting developing nations to meet the challenges of adaptation and mitigation.

We call on world leaders, including those meeting at the Gleneagles G8 Summit in July 2005, to:

Acknowledge that the threat of climate change is clear and increasing.

Launch an international study [5] to explore scientifically-informed targets for atmospheric greenhouse gas concentrations, and their associated emissions scenarios, that will enable nations to avoid impacts deemed unacceptable.

Identify cost-effective steps that can be taken now to contribute to substantial and long-term reduction in net global greenhouse gas emissions. Recognise that delayed action will increase the risk of adverse environmental effects and will likely incur a greater cost.

Work with developing nations to build a scientific and technological capacity best suited to their circumstances, enabling them to develop innovative solutions to mitigate and adapt to the adverse effects of climate change, while explicitly recognising their legitimate development rights.

Show leadership in developing and deploying clean energy technologies and approaches to energy efficiency, and share this knowledge with all other nations.

Mobilise the science and technology community to enhance research and development efforts, which can better inform climate change decisions.

Notes and references

1 This statement concentrates on climate change associated with global warming. We use the UNFCCC definition of climate change, which is 'a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods'.

2 IPCC (2001). Third Assessment Report. We recognise the international scientific consensus of the Intergovernmental Panel on Climate Change (IPCC).

3 IEA (2004). World Energy Outlook 4. Although long-term projections of future world energy demand and supply are highly uncertain, the World Energy Outlook produced by the International Energy Agency (IEA) is a useful source of information about possible future energy scenarios.

4 With special emphasis on the first principle of the UNFCCC, which states: 'The Parties should protect the climate system for the benefit of present and future generations of humankind, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities. Accordingly, the developed country Parties should take the lead in combating climate change and the adverse effects thereof'.

5 Recognising and building on the IPCC's ongoing work on emission scenarios.

Academia Brasiliera de Ciências Brazil
Royal Society of Canada, Canada
Chinese Academy of Sciences, China
Academié des Sciences, France
Deutsche Akademie der Naturforscher Leopoldina, Germany
Indian National Science Academy, India
Accademia dei Lincei, Italy
Science Council of Japan, Japan
Russian Academy of Sciences, Russia
Royal Society, United Kingdom
National Academy of Sciences, United States of America

11. Understanding and Responding to Climate Change (2005)




Understanding and Responding to Climate Change

There is a growing concern about global warming and the impact it will have on people and the ecosystems on which they depend. Temperatures have already risen 1.4°F since the start of the 20th century—with much of this warming occurring in just the last 30 years—and temperatures will likely rise at least another 2°F, and possibly more than 11°F, over the next 100 years. This warming will cause significant changes in sea level, ecosystems, and ice cover, among other impacts. In the Arctic, where temperatures have increased almost twice as much as the global average, the landscape and ecosystems are already changing rapidly.

Most scientists agree that the warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the atmosphere (see Figure 1). Greenhouse gases, such as carbon dioxide, have increased significantly since the Industrial Revolution, mostly from the burning of fossil fuels for energy, industrial processes, and transportation. Carbon dioxide levels are at their highest in at least 650,000 years and continue to rise.

There is no doubt that climate will continue to change throughout the 21st century and beyond, but there are still important questions regarding how large and how fast these changes will be, and what effects they will have in different regions. In some parts of the world, global warming could bring positive effects such as longer growing seasons and milder winters. Unfortunately, it is likely to bring harmful effects to a much higher percentage of the world's people. For example, people in coastal communities will likely experience increased flooding due to rising sea levels.

The scientific understanding of climate change is now sufficiently clear to begin taking steps to prepare for climate change and to slow it. Human actions over the next few decades will have a major influence on the magnitude and rate of future warming. Large, disruptive changes are much more likely if greenhouse gases are allowed to continue building up in the atmosphere at their present rate. However, reducing greenhouse gas emissions will require strong national and international commitments, technological innovation, and human willpower.

Global warming or climate change?

The phrase "climate change" is growing in preferred use to "global warming" because it helps convey that there are changes in addition to rising temperatures.

This brochure highlights findings and recommendations from National Academies' reports on climate change. These reports are the products of the National Academies' consensus study process, which brings together leading scientists, engineers, public health officials, and other experts to address specific scientific and technical questions. Such reports have evaluated climate change science, identified new avenues of inquiry and critical needs in the research infrastructure, and explored opportunities to use scientific knowledge to more effectively respond to climate change.

Figure 1. The greenhouse effect is a natural phenomenon that is essential to keeping the Earth’s surface warm. Like a greenhouse window, greenhouse gases allow sunlight to enter and then prevent heat from leaving the atmosphere. Water vapor (H2O) is the most important greenhouse gas, followed by carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), halocarbons, and ozone (O3). Human activities—primarily burning fossil fuels—are increasing the concentrations of these gases, amplifying the natural greenhouse effect. Image courtesy of the Marion Koshland Science Museum of the National Academy of Sciences.


Figure 2. Global surface temperature, based on surface air temperature measurements at meteorological stations and on sea surface temperature measurements from ships and satellites, shows a temperature increase of 1.4ºF (0.78ºC) since the beginning of the 20th century, with about 1.1ºF (0.61ºC) of the increase occurring in the past 30 years. Data courtesy of NASA Goddard Institute for Space Studies.

About the Science

Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

— Climate Change 2007: The Physical Basis, Intergovernmental Panel on Climate Change

The Earth is warming.

Temperature readings from around the globe show a relatively rapid increase in surface temperature during the past century (see Figure 2). These data, which have been closely scrutinized and carefully calibrated to remove potential problems such as the “urban heat island” effect, show an especially pronounced warming trend during the past 30 years—in fact, 9 of the 10 warmest years on record have occurred during the past decade. Furthermore, the surface temperature data are consistent with other evidence of warming, such as increasing ocean temperatures, shrinking mountain glaciers, and decreasing polar ice cover.

One inevitable question people ask is whether the current warming trend is unusual compared to temperature shifts on Earth prior to the 20th century—that is, before the buildup of excess greenhouse gases in the atmosphere. To help answer this question, scientists analyze tree rings, ice cores, ocean sediments, and a number of other “proxy” indicators to estimate past climatic conditions. These studies are important for understanding many aspects of Earth’s climate, including the natural variability of surface temperature over many centuries. Surface Temperature Reconstructions for the Last 2,000 Years (2006), produced in response to a request from Congress, assesses the scientific evidence used to estimate global temperature variations during the past two millennia, as well as how these estimates contribute to our understanding of global climate change. The report concludes, with a high level of confidence, that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period since at least A.D. 1600 (see Figure 3). Estimating the Earth’s global- average temperature becomes increasingly difficult going further back in time due to the decreasing availability of reliable proxy evidence, but the available evidence indicates that most regions are warmer now than at any other time since at least A.D. 900.

Human activities are changing climate.

Figure 3. Surface temperature reconstructions made by six different research teams (colored lines) are shown along with the instrumental record of global surface temperature (black line). Each team used a different method and different set of “proxy” data to produce its temperature estimate. The uncertainty in each reconstruction generally increases going backward in time (as indicated by the gray shading). All the curves indicate that the last few decades of the 20th century were warmer than any comparable period during at least the past four centuries, and probably longer. Source: Surface Temperature Reconstructions for the Last 2000 Years (National Research Council, 2006)

In May 2001, the White House asked the National Academy of Sciences to assess our current understanding of climate change by answering some key questions related to the causes of climate change, projections of future change, and critical research directions to improve understanding of climate change. Climate Change Science: An Analysis of Some Key Questions (2001) concluded that “changes observed over the last several decades are likely mostly due to human activities.” Additional evidence collected over the past several years has increased confidence in this conclusion.

How do we know that human activities are changing the Earth’s climate? The concurrent increase in surface temperature with carbon dioxide and other greenhouse gases during the past century is one of the main indications. Prior to the Industrial Revolution, the amount of carbon dioxide released to the atmosphere by natural processes was almost exactly in balance with the amount absorbed by plants and other “sinks” on the Earth’s surface. The burning of fossil fuels (oil, natural gas, and coal) releases additional carbon dioxide to the atmosphere. About half of this excess carbon dioxide is absorbed by the ocean, plants, and trees, but the rest accumulates in the atmosphere, amplifying the natural greenhouse effect. There is also considerable evidence that human activities are causing the increases in other greenhouse gases such as methane and nitrous oxide.

Rising temperatures and greenhouse gas concentrations observed since 1978 are particularly noteworthy because the rates of increase are so high and because, during the same period, the energy reaching the Earth from the Sun has been measured precisely by satellites. These measurements indicate that the Sun’s output has not increased since 1978, so the warming during the past 30 years cannot be attributed to an increase in solar energy reaching the Earth. The frequency of volcanic eruptions, which tend to cool the Earth by reflecting sunlight back to space, also has not increased or decreased significantly. Thus, there are no known natural factors that could explain the warming during this time period.

Additional evidence for a human influence on climate can be seen in the geographical pattern of observed warming, with greater temperature increases over land and in polar regions than over the oceans. This pattern is strongly indicative of warming caused by increasing greenhouse gas concentrations, as is the vertical profile of warming in the atmosphere and oceans. Further, model simulations of temperature change during the past century only match the observed temperature increase when greenhouse gas increases and other human causes are included (see Figure 4).

Figure 4. Model simulations of 20th century climate variations more closely match observed temperature when both natural and human influences are included. Black line shows observed temperatures. Blue- shaded regions show projections from models that only included natural forcings (solar activity and volcanos). Red-shaded regions show projections from models that include both natural and human forcings. Source: Climate Change 2007: The Physical Science Basis, Intergovernmental Panel on Climate Change 2007.

Figure 5. Various climate drivers, or radiative forcings, act to either warm or cool the Earth. Positive forcings, such as those due to greenhouse gases, warm the Earth, while negative forcings, such as aerosols, have a cooling effect. If positive and negative forcings remained in balance, there would be no warming or cooling. The column on the right indicates the level of scientific understanding (LOSU) for each forcing. Source: Climate Change 2007: The Physical Science Basis, Intergovernmental Panel on Climate Change 2007.

The Earth’s temperature is influenced by many factors.

Many different factors play a role in controlling Earth’s surface temperature. Scientists classify these factors as either climate forcings or climate feedbacks depending on how they operate. A forcing is something that is imposed externally on the climate system by either human activities or natural processes (e.g., burning fossil fuels or volcanic eruptions). Positive climate forcings, such as excess greenhouse gases, warm the Earth, while negative forcings, such as most aerosols produced by industrial processes and volcanic eruptions, cool the Earth (see Figure 5). In general, the cooling caused by aerosols is not as well understood as the warming caused by greenhouse gases.

Climate feedbacks, on the other hand, either amplify or dampen the response to a given forcing. A feedback is an energy change that is produced within the climate system itself in response to a climate forcing. During a feedback loop, a change in one factor, such as temperature, leads to a change in another factor, such as water vapor, which either reinforces or offsets the change in the first factor (see Figure 6a and 6b).

Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005) takes a close look at a range of different climate forcings. The report concludes that it is important to quantify how forcings cause changes in climate variables other than temperature. For example, regional changes in precipitation could have significant impacts on water availability for agricultural, residential, industrial, and recreational use.

What warms and cools the earth?

“Forcings” are things imposed externally on the climate system that can warm or cool the Earth. If positive and negative forcings remained in balance, there would be no warming or cooling.

Greenhouse gases warm the planet:

• Carbon dioxide (CO 2) has both natural and human sources, but CO2 levels are increasing primarily because of the use of fossil fuels, with deforestation and other land use changes also making a contribution. Increases in carbon dioxide are the single largest climate forcing contributing to global warming (see Figure 5).
• Methane (CH 4) has both human and natural sources, and levels have risen significantly since pre-industrial times due to human activities such as raising livestock, growing rice, filling landfills, and using natural gas (which releases methane when it is extracted and transported).
• Nitrous oxide (N2O) concentrations have risen primarily because of agricultural activities and land use changes.
• Ozone (O3) forms naturally in the upper atmosphere, where it creates a protective shield that intercepts damaging ultraviolet radiation from the Sun. However, ozone produced near the Earth’s surface via reactions involving carbon monoxide, hydrocarbons, nitrogen oxide, and other pollutants is harmful to both animals and plants and has a warming effect. The concentration of O3 in the lower atmosphere is increasing as a result of human activities.
• Halocarbons, including chlorofluorocarbons (CFCs), are chemicals that have been used for a variety of applications, such as refrigerants and fire retardants. In addition to being potent greenhouse gases, CFCs also damage the ozone layer. The production of most CFCs is now banned, so their concentrations are starting to decline.

Other human activities can also force temperature changes:

• Most aerosols (airborne particles and droplets), such as sulfate (SO4) cool the planet by reflecting sunlight back to space. Some aerosols also cool the Earth indirectly by increasing the amount of sunlight reflected by clouds. Human activities, such as industrial processes, produce many different kinds of aerosols. The total cooling that these aerosols produce is one of the greatest remaining uncertainties in understanding present and future climate change.
• Black carbon particles or “soot,” produced when fossil fuels or vegetation are burned, generally have a warming effect because they absorb incoming solar radiation. Black carbon particles settling on snow or ice are a particularly potent warmer.
• Deforestation and other changes in land use modify the amount of sunlight reflected back to space from the Earth’s surface. Changes in land use can lead to positive and negative climate forcing locally, but the net global effect is a slight cooling.

Natural processes also affect the Earth’s temperature:

• The Sun is Earth’s main energy source. The Sun’s output is nearly constant, but small changes over an extended period of time can lead to climate changes. In addition, slow changes in the Earth’s orbit affect how the Sun’s energy is distributed across the planet, giving rise to ice ages and other long-term climate fluctuations over many thousands of years. The Sun’s output has not increased over the past 30 years, so it cannot be responsible for recent warming.
• Volcanic eruptions emit many gases. One of the most important of these is sulfur dioxide (SO2), which, once in the atmosphere, forms sulfate aerosol (SO4). Large volcanic eruptions can cool the Earth slightly for several years, until the sulfate particles settle out of the atmosphere.

Another report, Understanding Climate Change Feedbacks (2003) examines what is known and not known about climate change feedbacks and identifies important research avenues for improving our understanding. A substantial part of the uncertainty in projections of future climate change can be attributed to an incomplete understanding of climate feedback processes. Enhanced research in the areas of climate monitoring and climate modeling are needed to improve understanding of how the Earth’s climate will respond to future climate forcings.

The magnitude of future climate change is difficult to project.

The Intergovernmental Panel on Climate Change (IPCC), which involves hundreds of scientists from the United States and other nations in assessing the state of climate change, concluded in a 2007 report that average global surface temperatures will likely rise by an additional 2.0–11.5oF (1.1–6.4oC) by 2100. This temperature increase will be accompanied by a host of other environmental changes, such as an increase in global sea level of between 0.59 and 1.94 feet (0.18 and 0.59 meters).

Figure 6a: This schematic illustrates just one of the dozens of climate feedbacks identified by scientists. The warming created by greenhouse gases leads to additional evaporation of water from the oceans into the atmosphere. But water vapor itself is a greenhouse gas and can cause even more warming. Scientists call this the “positive water-vapor feedback.”

Figure 6b. This schematic illustrates a negative feedback cycle. If evaporation from the oceans causes more low clouds to form, they will reflect more sunlight back into space, causing a slight decrease in surface temperatures. On the other hand, if increased ocean evaporation leads to the formation of more high clouds, the result would be a positive feedback cycle similar to the water-vapor feedback shown in Figure 6a.


A feedback is an energy change within the climate system in response to a climate forcing. For example:

• Water vapor (H2O) is the most potent and abundant greenhouse gas in Earth’s atmosphere. However, its concentration is controlled primarily by the rate of evaporation from the oceans and transpiration from plants, rather than by human activities, and water vapor molecules only remain in the atmosphere for a few days on average. Thus, changes in water vapor are considered a feedback that amplifies the warming induced by other climate forcings (see Figure 6a).
• Sea ice reflects sunlight back to space. Changes in sea ice are a positive climate feedback because warming causes a reduction in sea ice extent, which allows more sunlight to be absorbed by the dark ocean, causing further warming.
• Clouds reflect sunlight back to space, but also act like a greenhouse gas by absorbing heat leaving the Earth’s surface. Low clouds tend to cool (reflect more energy than they trap) while high clouds tend to warm (trap more energy than they reflect). The net effect of cloudiness changes on surface temperature depends on how and where the cloud cover changes, and this is one of the largest uncertainties in projections of future climate change (see Figure 6b).

Estimates of future climate change are typically called projections and are expressed as a range of possible outcomes. One reason for this uncertainty is because it is difficult to predict how human populations will grow, use energy, and manage resources, all of which will have a strong influence on future greenhouse gas emissions. There are also uncertainties about how the climate system will respond to rising greenhouse gas concentrations. For example, the IPCC’s estimate of future sea level rise does not take into account the possibility that ice sheets or glaciers could start melting more rapidly as the temperature rises.

It is very likely that increasing global temperatures will lead to higher maximum temperatures, more heat waves, and fewer cold days over most land areas. Some scientists believe that hurricanes may also become more intense as ocean temperatures rise, but others have argued that this intensification could be moderated or offset by other changes, such as changes in tropical winds or El Niño events.

One of the most important areas of uncertainty being investigated is regional climate change. Although scientists are beginning to project how the climate will change in specific regions and what some of the impacts of these changes might be, their level of confidence in these projections is not as high as for global climate change projections. In general, global temperature is easier to project than regional changes such as rainfall, storm patterns, and ecosystem impacts.

Complicating things further is the fact that the climate has changed abruptly in the past—within a decade—and could do so again. Abrupt changes, such as the Dust Bowl drought of the 1930s which displaced hundreds of thousands of people in the American Great Plains, take place so rapidly that humans and ecosystems have difficulty adapting to them. Abrupt Climate Change: Inevitable Surprises (2002) outlines some of the evidence for and theories about abrupt change. One theory is that melting ice caps could “freshen” the water in the North Atlantic, slowing down the natural ocean circulation that brings warmer Gulf Stream waters to the north and cooler waters south again (see Figure 7). Such a slowdown would make it much cooler in northern Europe.

Figure 7. A key mechanism in the circulation of water through the world’s oceans is the sinking of cold salty seawater. For example, in the Atlantic, oceanic currents transport warm, saline water to the North Atlantic where the water becomes denser as it is cooled by cold Arctic air. The chilled seawater sinks to the bottom, forming a southward- moving water mass. It has been hypothesized that large inputs of less dense fresh water from melting ice caps could disrupt ocean circulation by preventing the formation of chilled salty water. Such a disruption could trigger a host of climate changes such as cooling across much of northern Europe. Source: Impacts of a Warming Arctic: Arctic Climate Impact Assessment, p. 32.

The role of carbon dioxide in warming the Earth’s surface via the natural greenhouse effect was first proposed by Swedish scientist Svante Arrhenius more than 100 years ago. Arrhenius suggested that changes in carbon dioxide might explain the large temperature variations over the past several hundred thousand years known as the ice ages (see Figure 8a). Carbon dioxide appears to have acted like a feedback during these cycles, reinforcing temperature changes initiated by natural variations in Earth’s orbit. In contrast, carbon dioxide levels were nearly constant during the past several thousand years until human activities began emitting large amounts of carbon dioxide into the atmosphere, amplifying the natural greenhouse effect (see Figure 8b). Thus, while carbon dioxide may have acted as a feedback in the past, it is acting as a forcing in the current climate.

Figure 8a. (left) As ice core records from Vostok, Antarctica show, the temperature near the South Pole has varied by more than 20º F during the past 350,000 years in a regular pattern that constitutes the ice age/interglacial cycles. Changes in carbon dioxide concentrations (in blue) track closely with changes in temperature (in red) during these cycles, but carbon dioxide levels are now higher than at any time during the past 650,000 years. Image courtesy of the Marian Koshland Science Museum of the National Academy of Sciences.

Figure 8b. (right) Atmospheric concentrations of carbon dioxide during the past 10,000 years (large panel) and since 1750 (inset panel) show a rapid increase in carbon dioxide. Measurements are shown from ice cores (symbols with different colors for different studies) and atmospheric samples (the red line, which is data from the Keeling curve shown below). Source: Climate Change 2007: The Physical Science Basis, Intergovernmental Panel on Climate Change.
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Figure 9. Charles Keeling’s curve provides a precise record of atmospheric carbon dioxide (CO2) concentrations, which he began measuring in 1958. The steady upward trend shows increases in annual average CO2 concentrations. The sawtooth pattern seen in the Keeling curve is like the breathing of the planet. In the wintertime, carbon dioxide is released into the atmosphere by the decaying of vegetation from the previous growing season and by soil respiration. Then in the spring and summer of the following year, carbon dioxide is taken up by plants as they grow. Data source: Carbon Dioxide Information Analysis Center.


Our understanding of climate and how it has varied over time is advancing rapidly as new data are acquired and new investigative instruments and methods are employed.

—Ralph Cicerone, foreword of Surface Temperature Reconstructions for the Last 2000 Years, National Research Council, 2006

Observations and data are the foundation of climate science.

In the 1950s, long before the idea of human-induced climate change was prevalent, oceanographer Roger Revelle suggested that the sea could not absorb all the carbon dioxide being released from fossil fuel usage. Revelle made the first continual measurements of atmospheric carbon dioxide with the goal of better understanding the carbon cycle— how carbon is exchanged between plants, animals, the ocean, and the atmosphere. In 1958, Revelle’s colleague Charles Keeling began collecting canisters of air once or twice each week at the Mauna Loa Observatory, 11,000 feet above sea level in Hawaii, far away from major industrial and population centers. This remarkable 50-year dataset, known as the Keeling curve (see Figure 9, left), is a cornerstone of climate change science. Similar observations are now routinely made at stations across the globe.

Most of the observing systems used to monitor climate today were established to provide data for other purposes, such as predicting daily weather; advising farmers; warning of hurricanes, tornadoes, and floods; managing water resources; aiding ocean and air transportation; and understanding the ocean. Data used for climate research, however, have unique requirements. Higher accuracy and precision are often needed to detect gradual climate trends, observing programs must be sustained over long periods of time, and observations are needed at both global scales and at local scales to serve a range of climate information users.

A key requirement for climate change science is the ability to generate, analyze, and archive long-term climate data records in order to make ongoing assessments of the state of the environment. Climate Data Records from Environmental Satellites (2004) defines a climate data record as a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change. The report identifies several elements of successful climate data record generation programs that range from effective, expert leadership to a long-term commitment to sustaining observations and archives.

Climate science relies on a wide range of data sources.

Figure 10. (top left) The Landsat satellite series has provided continuous record of the Earth’s continental surfaces since 1972, providing critical information for global change research. Image courtesy of the NASA Goddard Space Flight Center. (bottom left) Weather stations, both on land and floating on buoys moored at sea, provide regular measurements of temperature, humidity, winds, and other atmospheric properties. Image courtesy of TAO Project Office, NOAA Pacific Marine Environmental Laboratory. (right) Weather balloons, which carry instruments known as radiosondes, provide vertical profiles of some of these same properties throughout the lower atmosphere. Image © University Corporation for Atmospheric Research.

What’s the Difference Between Weather and Climate?

Weather refers to hour-to-hour and day-to-day changes in temperature, cloudiness, precipitation, and other meteorological conditions. Climate is commonly thought of as the average weather conditions at a given location over time, but it also includes more complicated statistics such as the average daytime maximum temperature each month and the frequency of storms or droughts. Climate change refers to changes in these statistics over years, decades, and even centuries. The term global change is sometimes used to include these and other environmental changes, such as deforestation, ozone depletion, and the acidification of the world’s oceans because of rising carbon dioxide levels.

The accuracy of weather forecasts can be confirmed by observing the actual weather. Climate models, on the other hand, produce projections many years into the future, making them difficult to verify. Further, climate models must take into account a much larger number of variables, such as changes in ocean circulation, vegetation, and greenhouse gas concentrations. Climate models have been shown to accurately simulate a number of past climate changes, including the cooling observed after major volcanic eruptions, global temperature change during the 20th century, and even the ice ages, so our confidence in these models is increasing.

Climate scientists rely on data collected using a wide array of observing systems, operated by various government agencies, universities, and other domestic and international groups (see Figure 10). For example, surface temperature measurements are taken by both humans and automated instruments at fixed stations on land and on buoys in the ocean, and also on ocean-going ships. Measurements of temperatures at different heights in the atmosphere are obtained primarily from weather balloons and satellites. All measurements go through rigorous quality control procedures and must be carefully calibrated to account for changes in measuring technology. Having multiple independent data sources is important for detecting and removing biases and other errors.

Space-based observations are especially important for monitoring present and future climate change because they offer a unique vantage point and can take measurements over the entire surface of the Earth. Earth Science and Applications from Space: Urgent Needs and Opportunities to Serve the Nation (2005) examines the current and planned system of U.S. environmental satellites, including the satellites needed to observe climate change, and concludes that the system is “at risk of collapse.” A subsequent report, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (2007), presents a prioritized list of space programs, missions, and supporting activities that would restore the satellite observations needed to address the most important environmental issues of the next decade and beyond, including climate change.

Scientists have also developed a variety of methods for estimating how the Earth’s climate varied prior to the mid-19th century, when thermometer measurements first became widely available (see Figure 11). For example, ice cores are drilled in polar and mountain ice caps and analyzed to reconstruct past climate changes; in addition to analyzing the isotopes of hydrogen and oxygen atoms that make up the ice to infer past temperatures in the region, the bubbles trapped in the ice can be sampled to determine past concentrations of greenhouse gases. Tree rings, corals, ocean and lake sediments, cave deposits, and even animal nests have also been analyzed to estimate past variations in climate.

Figure 11. Scientists infer past temperatures using several different methods: ice cores from polar ice caps and mountain glaciers (left) provide samples of past atmospheres frozen in the ice—the deeper you go, the further back in time. Temperature is inferred by examining characteristics of the hydrogen and oxygen atoms that make up the ice, among other data. Tree rings (right) can reveal past climate conditions based on the width of each annual ring and many other characteristics, such as density of the wood in each ring. Other types of samples used to infer past climate include marine sediments and soil samples. Ice core photo courtesy of the National Geophysical Data Center. Tree ring photo courtesy of Connie Woodhouse.

Figure 12. Climate models often are used to help inform policy decisions. The graph on the left shows the projected global mean temperature change for several different scenarios of future emissions based on assumptions of future population growth, economic development, life style choices, technological change, and availability of energy alternatives. Each line represents the average of many different models run using the same scenario. The images on the right show the projected geographical pattern of annual mean surface air temperature changes at the end of the century (relative to the average temperatures for the period 1980–1990) for the scenarios A2 and B1 (red and blue lines). The projected warming by the end of the 21st century is less extreme in the B1 scenario, which assumes significant reductions in greenhouse gas emissions, than in the A2 scenario, which assumes “business as usual.” In both scenarios, land areas are expected to warm more than oceans, and the greatest warming is projected at high latitudes. Source: Climate Change 2007: The Physical Science Basis, Intergovernmental Panel on Climate Change 2007.

Various human records can also be used to reconstruct past climate conditions. Shipping records have been analyzed to estimate changes in the frequency of hurricanes in the Atlantic Ocean during the past 150 years. In Burgundy, France, monastery archives record the timing of the pinot noir harvest back to 1370, which provides information about climate, and similar records exist for the blossoming dates of cherry trees and other flowering plants in Japan and China. Records of Alpine glacier length, some derived from paintings and other documentary sources, have even been used to reconstruct surface temperature variations in south-central Europe for the past several centuries.

Models help illuminate the many dimensions of climate change.

Climate models are important tools for understanding how different components of the climate system operate today, how they may have functioned differently in the past, and how the climate might evolve in the future in response to forcings from both natural processes and human activities. Climate models use mathematical equations to represent the climate system, first modeling each system component separately and then linking them together to simulate the full Earth system. These models are run on advanced supercomputers.

Since the late 1960s, when climate models were pioneered, their accuracy has increased as computing power and our understanding of the climate system have improved. Improving Effectiveness of U.S. Climate Modeling (2001) offered several recommendations for strengthening climate modeling capabilities in the United States. The report identified a shortfall in computing facilities and highly skilled technical workers devoted to climate modeling as two important problems. Several of the report’s recommendations have been adopted since it was published, but concerns remain about whether the United States is training enough people to work on climate change issues.

Social science helps us understand how human choices affect climate.

Research on the social and behavioral sciences is essential for understanding and responding to climate change. Research on the human dimensions of global change focuses on four general areas: (1) human activities that alter the Earth’s environment, (2) the forces that drive these activities, (3) the consequences of environmental changes for societies and economies, and (4) how humans respond to these changes. Global Environmental Change: Understanding the Human Dimensions (1992) develops a conceptual framework for combining the efforts of natural and social scientists to better understand how human actions influence global change.

Although fossil fuel burning is the most significant human activity contributing to climate change, other activities also have significant influences. For example, landuse changes, such as the conversion of forests and wetlands to agricultural or urban uses, have a strong influence on both local and global climate. Population, Land Use, and Environment (2005) looks at the many demographic factors—including population growth, density, fertility, mortality, and the age and sex composition of households— that are known to affect land use and land cover change. The report identifies the research needed to better understand these connections.

Much of the uncertainty about how the climate will change during the next 100 years is due to an inability to predict how population growth, economic development, energy and land use, and other human activities will evolve. To illustrate how various human choices affect future climate change, climate models are typically run using a number of different “scenarios,” each of which is designed to represent a plausible and internally consistent prediction of future human activities (see Figure 12). Improving these scenarios depends on progress in understanding changes in human behavior and how these changes affect climate forcing.

Federally Coordinated Research on Climate Change

More than a dozen federal agencies are involved in producing and using climate change data and research. The first efforts at a coordinated government research strategy culminated in the creation of the U.S. Global Change Research Program (USGCRP) in 1989. USGCRP made substantial investments in understanding the underlying processes of climate change, documenting past and ongoing global change, improving modeling, and enhancing knowledge of El Niño and the ability to forecast it.

The U.S. Climate Change Science Program (CCSP) was formed in February 2002 as a new management structure to coordinate government activities on climate. The CCSP has asked the National Academies to provide independent advice on numerous aspects of the program, including a two-stage review of its strategic plan, metrics for evaluating the progress of the program, scientific reviews of assessment reports, and ongoing strategic advice on the program as a whole.

Evaluating Progress of the U.S. Climate Change Science Program (2007) concluded that the program has made good progress in documenting and understanding temperature trends and related environmental changes, and the influence of human activities on these observed changes. The ability to predict future climate changes has improved, but efforts to understand the impacts of climate changes on society and analyze mitigation and adaptation strategies are still relatively immature. The program also had not yet met expectations in supporting decision making, studying regional impacts, and communicating with a wider group of stakeholders.



Many of the world’s poorest people, who lack the resources to respond to the impacts of climate change, are likely to suffer the most.

—Joint science academies’ statement on sustainability, energy efficiency, and climate protection (May 2007)

Climate change will have many kinds of impacts.

Climate change will affect ecosystems and human systems—such as agricultural, transportation, and health infrastructure—in ways we are only beginning to understand (see Figure 13). There will be positive and negative impacts of climate change, even within a single region. For example, warmer temperatures may bring longer growing seasons in some regions, benefiting those farmers who can adapt to the new conditions but potentially harming native plant and animal species. In general, the larger and faster the changes in climate are, the more difficult it will be for human and natural systems to adapt.

The Chinstrap penguin: a regional winner. Even within a single regional ecosystem, there will be winners and losers. For example, the population of Adélie penguins has decreased 22 percent during the past 25 years, while the Chinstrap penguin population increased by 400 percent. The two species depend on different habitats for survival: Adélies inhabit the winter ice pack, whereas Chinstraps remain in close association with open water. A 7-9° F rise in midwinter temperatures on the western Antarctic Peninsula during the past 50 years and associated receding sea-ice pack is reflected in their changing populations.

Unfortunately, the regions that will be most severely affected are often the regions that are the least able to adapt. Bangladesh, one of the poorest nations in the world, is projected to lose 17.5 percent of its land if sea level rises about 1 meter (39 inches), displacing millions of people. Several islands in the South Pacific and Indian oceans may disappear. Many other coastal regions will be at increased risk of flooding, especially during storm surges, threatening animals, plants, and human infrastructure such as roads, bridges, and water supplies.

Developed nations, including the United States, also will be affected. For example, most models indicate that snowpack is likely to decline on many mountain ranges in the West, which would bring adverse impacts on fish populations, hydropower, water recreation, and water availability for agricultural, industrial, and residential use. However, wealthy nations have a better chance of using science and technology to anticipate and adapt to sea level rise, threats to agriculture, and other climate impacts. Adaptations measures could include revising construction codes in coastal zones or the development of new agricultural technologies. Developing nations will need assistance in building their capacity to meet the challenges of adapting to climate change.

Global changes most keenly felt in polar regions. Recent years have brought a flurry of dramatic changes in the polar environment— Changes that are happening faster than at other latitudes and faster than scientists had expected. Glaciers and sea ice are melting more and more quickly. Thawing permafrost can cause houses to sink, create forests of “drunken trees” that tilt at odd angles, and weaken roads, runways, and pipelines. Photo courtesy Larry Hinzman.

Polar regions are already experiencing major changes in climate.

Like the proverbial canary in the coal mine, changes in the polar regions can be an early warning of things to come for the rest of the planet, and the environmental changes now being witnessed at higher latitudes are alarming. For example, Arctic sea ice cover is decreasing rapidly and glaciers are retreating and thinning (see Figure 14, next page), NASA data show that Arctic sea ice shrunk to a new record low in 2007; 24 percent lower than the previous record (2005), and 40 percent lower than the long-term average.

Figure 13. Climate changes could have potentially wide-ranging effects on both the natural environment and human activities and economies. Source: U.S. Environmental Protection Agency.

A number of ecosystem changes, such as plants flowering earlier in the year and declines in animal species that depend on sea ice for habitat, have been attributed to the strong warming observed at northern latitudes. Changing climate is also having human impacts: some Alaskan villages have been moved to higher ground in response to increasing storm damage, and the thawing of permafrost is undermining infrastructure, affecting houses, roads, and pipelines in northern communities around the world.

Given the global significance of changes in the polar regions, it is vital to have observational records that are sufficiently complete to both understand what is happening and guide decision makers in responding to change. A Vision for the International Polar Year 2007-2008 (2004) recommends that the IPY 2007-2008—an unprecedented multinational effort to better understand the polar regions—be used as an opportunity to design and implement multidisciplinary polar observing networks. The Arctic has an especially limited record of observations that are often few and far between, short-term, and not coordinated with related observations. Toward an Integrated Arctic Observing Network (2006) recommends building a network that delivers complete pan-arctic observations.

Figure 14. Warmer temperatures are causing glaciers to recede, as illustrated by theses photos of South Cascade Glacier in the state of Washington. Photo courtesy of Andrew Fountain.

Climate and Human Health

There are many ways in which climate change might affect human health, including heat stress, increased air pollution, and food scarcities due to drought or other agricultural stresses. Because many disease pathogens and carriers are strongly influenced by temperature, humidity, and other climate variables, climate change may also influence the spread of infectious diseases or the intensity of disease outbreaks. For example, some studies have predicted that global climate change could lead to an increase in malaria transmission by expanding mosquito habitat.

Current strategies for controlling infectious disease epidemics rely primarily on surveillance and response. Under the Weather: Climate, Ecosystems, and Infectious Disease (2001) recommends a shift toward prediction and prevention, such as developing early warning systems. Overall vulnerability to infectious disease could be reduced through water treatment systems, vaccination programs, and enhanced efforts to control disease carriers. The report also recommends increasing interdisciplinary collaboration among climate modelers, meteorologists, ecologists, social scientists, and medical and health professionals to better understand the linkages between climate change and disease.



Policymakers look to climate change science to answer two big questions: what could we do to prepare for the impacts of climate change, and what steps might be taken to slow it?

—Richard Alley, Professor, Pennsylvania State University

How Science Informs Decision-making

Steps can be taken to prepare for climate change.

Climate information is becoming increasingly important to public and private decision-making in various sectors, such as emergency management, water management, insurance, irrigation, power production, and construction. The emerging ability to forecast climate at seasonal-to-interannual time scales can be of tremendous value if the information is used well. Making Climate Forecasts Matter (1999) identifies research directions toward more useful seasonal-to-interannual climate forecasts and how to use forecasting to better manage the human consequences of climate change.

There is a wealth of climate data and information already collected that could be made useful to decision-makers in the form of “climate services.” Such efforts are analogous to the efforts of the National Weather Service to provide useful weather information. A Climate Services Vision: First Steps Towards the Future (2001) outlines principles for improving climate services: for example, climate data should be made as user-friendly as weather information is today, and the government agencies, businesses, and universities involved in climate change data collection and research should establish active and well- Defined connections to users and potential users.

Weather forecasts have benefited from a long and interactive history between providers and users, but this kind of communication is only beginning to develop in climate science. For example, western states have traditionally relied on January snowpack surveys to project annual streamflows. During the past several years, climate scientists have worked with water management agencies to develop streamflow projections based on increasingly reliable El Niño predictions, which are available several months ahead of the January surveys and thus allow greater management flexibility. Research and Networks for Decision Support in the NOAA Sectoral Applications Research Program (2007) identifies additional ways to build communications between producers and users of climate information.

Another way to prepare for climate change is to develop practical strategies for reducing the overall vulnerability of economic and ecological systems to weather and climate variations. Some of these are “no-regrets” strategies that will provide benefits regardless of whether a significant climate change ultimately occurs in a region. No-regrets measures could include improving climate forecasting based on decision-maker needs; slowing biodiversity loss; improving water, land, and air quality; and making our health care enterprise, financial markets, and energy and transportation systems more resilient to major disruptions.

Steps can be taken to mitigate climate change.

Despite remaining unanswered questions, the scientific understanding of climate change is now sufficiently clear to justify taking steps to reduce the amount of greenhouse gases in the atmosphere. Because carbon dioxide and other greenhouse gases can remain in the atmosphere for many decades, centuries, or longer, the climate change impacts from greenhouse gases emitted today will likely continue well beyond the 21st century. Failure to implement significant greenhouse gas emission reductions now will make it much more difficult to stabilize atmospheric concentrations at levels that avoid the most severe impacts.

Climate Data Inform Water Management Decisions in Colorado

Studies of past climate and streamflow conditions of the Colorado River Basin have shed new light on long-term water availability in the region. Water management decisions have been based on the past 100 years of recorded streamflows. However, studies reveal many periods in the past when streamflow was much lower than at any time in the past 100 years of recorded flows. Colorado River Basin Water Management (2007) concludes that managers are therefore basing decisions on an overly optimistic forecast of future water availability, particularly given regional warming trends. The report recommends that Colorado prepare for possible water shortages that can not be overcome through current technology and management practices. Photo of Lake Powell, courtesy of Brad Udall, University of Colorado.


Governments have proven they can work together to reduce or reverse negative human impacts on nature. A classic example is the successful international effort to phase out use of chlorofluorocarbons (CFCs) in aerosol sprays and refrigerants, which were destroying the Earth’s protective ozone layer. Although the success of controls on CFCs cannot be denied, the problem of controlling greenhouse gas emissions is much more difficult: alternative technologies are not readily available to offset many human activities that contribute to climate change, and, instead of the handful of companies responsible for producing CFCs, there are literally billions of individuals, as well as many businesses and governments, making decisions that affect carbon dioxide and other greenhouse gas emissions.

At the present time there is no single solution that can eliminate future warming. However, as early as 1992, Policy Implications of Greenhouse Warming (1992) concluded that there are many potentially cost-effective technological options that could help stabilize greenhouse gas concentrations. Personal, national, and international choices have an impact; for example driving less, regulating emissions, and sharing energy technologies would all help reduce emissions. The climate change problem is one of the most difficult problems of managing the “commons”—environmental goods that benefit everyone but that can be degraded by the individual actions of anyone. Social scientists are working to identify social institutions that are suitable for managing commons problems, such as greenhouse gas emissions.

The increasing need for energy is the single greatest challenge to slowing climate change.

Energy is essential for all sectors of the economy, including industry, commerce, transportation, and residential use. Worldwide energy use continues to grow with economic and population expansion. Fossil fuels supply most of today’s energy needs. According to the Department of Energy, about 82 percent of all greenhouse gases produced in the United States by human activity comes from burning fossil fuels. Developing countries, China and India in particular, are rapidly increasing their use of energy, primarily from fossil fuels, and consequently their carbon dioxide emissions are rising sharply (see Figure 15, next page).

Carbon dioxide emissions can be reduced either by switching to alternative fuels that produce less or no carbon dioxide or by using energy more efficiently. Energy efficiency could be improved in all sectors of the U.S. economy. Many of these improvements are cost- effective, but constraints such as a lack of consumer awareness and higher initial costs hold them back. Energy Research at DOE: Was It Worth It? (2001) addresses the benefits of increasing the energy efficiency of lighting, refrigerators, and other appliances.

Informing Policy through Assessments

Climate change assessments are collective, deliberative processes by which experts review, analyze, and synthesize scientific knowledge to provide information for decision- aking or about remaining scientific uncertainties. One of the most influential set of assessments on climate change is produced by the Intergovernmental Panel on Climate Change (IPCC), which was established by the World Meteorological Organization and the United Nations Environment Programme to assess scientific, technical, and socioeconomic information relevant for the understanding of climate change. IPPC’s fourth assessment report was issued in 2007. Analysis of Global Change Assessments: Lessons Learned (2007) identifies the key elements of effective assessments, such as the development of tools that make use of scientific analyses at the regional and local level where decisions are made.

Oil is the main fuel in the transportation sector. Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards (2002) evaluates car and light truck fuel use and analyzes how fuel economy could be improved. Steps range from improved engine lubrication to hybrid vehicles.

Personal, national, and international choices have an impact. For example, driving less, regulating emissions, and sharing energy technologies would all help reduce emissions.

There are many alternatives to producing energy from fossil fuels. Electricity can be produced without significant carbon emissions using nuclear power and renewable energy technologies, such as solar, wind, hydropower, and biomass (fuels made from plant matter). Biofuels can also be used to power vehicles. Interest in these technologies is growing, and research and development could make all of them more viable, but each renewable energy technology carries its own set of issues and challenges. For example, Water Implications of Biofuels Production in the United States (2008) concludes that although ethanol and other biofuels can help reduce our nation’s dependence on fossil fuels, the increase in agriculture to grow biofuel crops, such as corn, could have serious impacts on water quality due to more intense use of fertilizers and increased soil erosion.

Another way to reduce emissions is to collect carbon dioxide from fossil-fuel-fired power plants and sequester it in the ground or the ocean. Novel Approaches to Carbon Management: Separation, Capture, Sequestration, and Conversion to Useful Products (2003) discusses the development of this technology. If successful, carbon sequestration could weaken the link between fossil fuel use and greenhouse gas emissions, but considerable work remains before this approach can be widely adopted.

Capturing carbon dioxide emissions from the tailpipes of vehicles is essentially impossible, which is one factor that has led to considerable interest in hydrogen as a fuel. However, as with electricity, hydrogen must be manufactured from primary energy sources. If hydrogen is produced from fossil fuels (currently the least expensive method), carbon capture and sequestration would be required to reduce net carbon dioxide emissions. Substantial technological and economic barriers in all phases of the hydrogen fuel cycle must also be surmounted. The Hydrogen Economy: Opportunities, Costs, Barriers and R&D Needs (2004) presents a strategy that could lead eventually to production of hydrogen from a variety of domestic sources—such as coal with carbon sequestration, nuclear power, wind, or photo-biological processes—and its efficient use in fuel-cell vehicles.

Figure 15. The two panels compare CO2 emissions per nation in 2005 and projections for 2030. In 2005, the largest emitter of CO2 was the United States, which is responsible for 25 percent of global emissions. By 2030, China and the developing world are expected to have significantly increased their CO2 emissions relative to the United States. Image courtesy of the Marian Koshland Science Museum of the National Academy of Sciences, updated 2007.

Continued scientific efforts to address a changing climate

Although the understanding of climate change has advanced significantly during the past few decades, many questions remain unanswered. The task of mitigating and adapting to the impacts of climate change will require worldwide collaborative input from a wide range of experts, including physical scientists, engineers, social scientists, medical scientists, business leaders, economists, and decision-makers at all levels of government. It is important to continue to improve our understanding of climate change science, and to make sure that available climate information more fully addresses the needs of decision makers. Through its expert consensus reports, the National Academies will continue to provide analysis and direction to the policymakers and stakeholders involved in understanding and responding to climate change.


Climate Change and related Reports from the National Academies

Highlighted in this booklet

Water Implications of Biofuels Production in the United States (2008)

Analysis of Global Change Assessments: Lessons Learned (2007)

Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability (2007)

Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (2007)

Evaluating Progress of the U.S. Climate Change Science Program (2007)

Research and Networks for Decision Support in the NOAA Sectoral Applications Research Program (2007)

Surface Temperature Reconstructions for the Last 2000 Years (2006)

Toward an Integrated Arctic Observing Network (2006)

Earth Science and Applications from Space: Urgent Needs and Opportunities to Serve the Nation (2005)

Population, Land Use, and the Environment (2005)

Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005)

Thinking Strategically: The Appropriate Use of Metrics for the Climate Change Science Program (2005)

A Vision for the International Polar Year 2007-2008 (2004)

Climate Data Records from Environmental Satellites (2004)

The Hydrogen Economy: Opportunities, Costs, Barriers and R&D Needs (2004)

Implementing Climate and Global Change Research: A Review of the Final U.S. Climate Change Science Program Strategic Plan (2004)

Novel Approaches to Carbon Management: Separation, Capture, Sequestration, and Conversion to Useful Products (2003)

Planning Climate and Global Change Research: A Review of the Draft U.S. Climate Change Science Program Strategic Plan (2003)

Understanding Climate Change Feedbacks (2003)

Abrupt Climate Change: Inevitable Surprises (2002)

Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards (2002)

A Climate Services Vision: First Steps Towards the Future (2001)

Climate Change Science: An Analysis of Some Key Questions (2001)

Energy Research at DOE: Was It Worth It? Energy Efficiency and Fossil Energy Research from 1978 to 2000 (2001)

Improving the Effectiveness of U.S. Climate Modeling (2001)

Under the Weather: Climate, Ecosystems, and Infectious Disease (2001)

Making Climate Forecasts Matter (1999)

Global Environmental Change: Understanding the Human Dimension (1992)

Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base (1992)

For more studies and related information see and National Academies reports are available from the National Academies Press, 500 Fifth Street, NW, Washington, DC 20001; 800-624-6242; Reports are available online in a fully searchable format.


About the National Academies

The National Academies are nongovernment, nonprofit organizations that were set up to provide independent scientific and technological advice to the U.S. government and nation. The National Academies include three honorary societies that elect new members to their ranks each year—the National Academy of Sciences, National Academy of Engineering, and Institute of Medicine—and the National Research Council, the operating arm that conducts the bulk of the institution's science policy and technical work. The Academies enlist committees of the nation's top scientists, engineers, and other experts, all of whom volunteer their time to study specific issues and concerns.

The National Academies offer the following e-mail newsletters and notifications related to climate change:

Earth & Life Studies at the National Academies, (immediate notification of new projects, committee postings, reports, and events)

Climate and Global Change at the National Academies e-update, (monthly)

The Board on Atmospheric Sciences and Climate Newsletter, (quarterly)

For more information, contact the Board on Atmospheric Sciences and Climate at 202-334-3512 or visit http:// This brochure was prepared by the National Research Council based on National Academies’ reports. It was written by Amanda Staudt, Nancy Huddleston, and Ian Kraucunas and was designed by Michele de la Menardiere. Support for this publication was provided by the Presidents’ Circle Communications Initiative of the National Academies. Thanks to Antonio Busalacchi, Richard Alley, Sherry Rowland, Dennis Hartmann, Tom Vonder Haar, Tom Wilbanks, Taro Takahashi, Alan Crane, Art Charo, Chris Elfring, Paul Stern, and Gregory Symmes for their helpful contributions.

2008 edition © National Academy of Sciences.

At a time when responding to our changing climate is one of the nation’s most complex endeavors, reports from the National Academies provide thoughtful analysis and helpful direction to policymakers and stakeholders.

These reports are produced by committees organized by the Board on Atmospheric Sciences and Climate, its Climate Research Committee, and numerous other entities within the National Academies. With support from sponsors, the National Academies will continue in its science advisory role to the agencies working on understanding changing climate, documenting its impacts, and developing effective response strategies.

12. Global Climate Change Impacts in the United States (2009)

13. IPCC Fourth Assessment Report, Summary for Policymakers (2007)

14. IPCC Fourth Assessment Report, Summary for Policymakers (2007)


Florida Officials Ban the Term "Climate Change"
by Katie Valentine
March 9, 2015

While Florida faces major threats from climate change and its impacts, an unwritten ban on mentioning “climate change” was passed in the state. Officials at Florida’s DEP and Gov. Rick Scott are to blame for such denial.

Florida’s Department of Environmental Protection is tasked with protecting the state’s “air, water and land.” But there’s one environmental threat you won’t hear DEP officials talking about.

Officials at Florida’s DEP have banned the words “climate change” and “global warming” from all official communications, including reports and emails, according to an investigation published Sunday by the Florida Center for Investigative Reporting (FCIR).

Four former DEP employees told FCIR that they had been instructed not to use the terms during their time at the state’s DEP.

“We were told not to use the terms ‘climate change,’ ‘global warming’ or ‘sustainability,’” Christopher Byrd, who served as an attorney with the DEP’s Office of General Counsel from 2008 to 2013, told FCIR. “That message was communicated to me and my colleagues by our superiors in the Office of General Counsel.”

The DEP’s press secretary Tiffany Cowie disagreed with these reports, however, saying that her department “does not have a policy on this.” But according to the former employees’ accounts, the unofficial policy went into place after Gov. Rick Scott (R) took office in 2011 and appointed a new DEP director. Over the last year, Scott has skirtedanswering questions on his views on climate change. He said in 2010 that he had “not been convinced” that climate change was real, but during last year’s gubernatorial race, he refused to take a stand on the issue. In August, five Florida climate scientists sat down with Scott in an attempt to explain the science behind climate change and the effects it’s having in Florida, but the scientists left the meeting feeling unsure that the governor had gotten the message.

The ban on using “climate change” and “global warming at the DEP manifested in a variety of ways, FCIR writes. One writer wanted to include climate change in a series of fact sheets he was writing on coral reefs for the state’s Coral Reef Conservation Program, but he said he was instructed not to by DEP employees. In addition, when volunteers attended a 2014 meeting the Coral Reef Conservation Program held to train volunteers to conduct presentations on coral reef health in Florida, two volunteers said they were told not to address climate change when talking about threats facing coral reefs.

“I told them the biggest problem I have was that there was absolutely no mention of climate change and the affect of climate change on coral reefs,” Doug Young, president of the South Florida Audubon Society and a member of the Broward County Climate Change Task Force who attended the meeting, told FCIR. “The two young women, really good people, said, ‘We are not allowed to show the words, or show any slides that depicted anything related to climate change.’”

An unwritten ban on mentioning “climate change” is concerning for an environmental agency in any state, but Florida in particular faces major threats from climate change and its impacts. The state has been called “ground zero” for sea level rise, an impact that’s already causing problems in parts of South Florida. The FCIR notes that the state doesn’t have any ban on talking about sea level rise, but it’s hard to address sea level rise without also addressing the broader problem of climate change. And on a federal level, Florida hasn’t been great at doing either: Scott announced last month that $106 million of his proposed budget would go towards ways to mitigate the impacts of sea level rise in Florida, but his re-election environmental plan published last year didn’t mention climate change.

It's so bright in Florida that everyone wears sunglasses

[Zaphod] Hey, spooky, eh? And dark.

[Ford] You've still got your sunglasses on.

[Zaphod] Too right!


[Trillian] Look at this! Any idea what those strange symbols on the walls are, Zaphod?

[Zaphod] Yeah! They're strange symbols of some kind. It's hard to tell with my shades on!

[Ford] I wish I had heads like you, Zaphod. I could have endless fun bashing them against walls!

[Zaphod] Hey, don't bug me, Ford!

[Zaphod2] Yeah!

[Ford] Yeah?

[Zaphod] Yeah! These are the greatest shades in the known sky! Look at the copy.


[Ford] "Joo janta 200 SuperChromatic Peril-Sensitive sunglasses. To help you develop a relaxed attitude to danger. At the first hint of trouble, they turn black and thus prevent you from seeing anything that might alarm you." You're mad!


[Trillian] I thought I just saw a movement down at the end of the corridor!

[Zaphod] No ... it's just shadows ... There's no one here. Trust me.

[Ford] Zaphod, mate, I'd trust you as far as I could comfortably spit a rat!

[Zaphod] This is a dead planet, man!

[Trillian] There's definitely something there.

[Zaphod] No ...



-- The Hitchhiker's Guide to the Galaxy, directed by Douglas Adams
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