Study Says Hurricanes Are Getting Stronger
by Sharon Begley
Staff Reporter of THE WALL STREET JOURNAL
August 1, 2005
Charley, Jeanne, Ivan and Frances caused a record-setting $20 billion in insured losses when they blew through Florida last year. But if scientists are right, that record for hurricane damage will prove short-lived.
Hurricanes have been lasting longer and hitting harder since the mid-1970s, and in the coming years global warming is likely to increase the storms' destructiveness, according to a study released yesterday.
The link between global warming and hurricanes (or cyclones, as they are known globally) has been one of the most controversial in the field of climate change. Last year, a U.S. government scientist resigned from the international panel that assesses climate change, charging that a fellow panel member had made baseless statements connecting hurricanes and human-caused global warming.
But now a consensus may be emerging on how a warmer world is affecting hurricanes. In the latest study, Kerry Emanuel of the Massachusetts Institute of Technology calculates that the storms' power -- a combination of the energy they pack and how long they last -- "has increased markedly since the mid-1970s." His report in the online edition of the journal Nature says since 1970, the power of storms in the North Atlantic has tripled, while the power of those in the western North Pacific has more than doubled.
The rise in cyclones' intensity and duration fits with both basic science and computer simulations of climate. As the temperatures at the surface of the ocean rise, so should wind speeds, since they draw their power from heat. Higher winds take longer to dissipate. But the surge in intensity has been even greater than predicted based on warmer ocean temperatures, Prof. Emanuel says.
How a warming world will affect the number of cyclones spawned each year remains unclear. There has been no clear trend in the frequency of hurricanes.
Prof. Emanuel does think human activities are behind the increasing power of storms. Natural climate changes affect the world's seas, but the recent rise in sea-surface temperatures, especially in the cyclone-forming tropics, "is unprecedented either historically or in the paleoclimatic record," Prof. Emanuel says, "and probably reflects the effect of global warming."
Other scientists are reaching the same conclusion. Sea-surface temperatures from 1995 to 2004 set records, atmospheric scientist Kevin Trenberth of the National Center for Atmospheric Research, part of the U.S. Department of Commerce, reported this spring in the journal Science, and he attributes that to "human-influenced environmental changes."
Even if human activities are intensifying hurricanes, however, there may be better solutions than reducing the emission of heat-trapping "greenhouse" gases, says environmental-policy expert Roger Pielke Jr., of the University of Colorado, Boulder. Stronger building codes and policies that keep people from building and rebuilding in hurricane-prone regions are much more cost effective, he argues.
The field of hurricanes and climate change is churning so fast that papers written only last year are obsolete. Prof. Emanuel co-authored one, accepted but not yet published by a leading meteorology journal, that concludes there is "only weak evidence of a systematic increase" in storm intensity. "We make a lot of statements in there about the unimportance of global warming [for cyclone intensity], statements I don't subscribe to anymore," says Prof. Emanuel. "I said I would have to withdraw as a co-author."