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Winter 2004, updated June 2006
Kevin Trenberth is head of the Climate Analysis Section in the Climate and Global Dynamics Division of NCAR's Earth System Laboratory.
Please note: This page provided for archival purposes; for current research, please see
Trenberth, K. E., and D. J. Shea (2006), "Atlantic hurricanes and natural variability in 2005," Geophysical Research Letters, 27 June, 33, L12704.
Trenberth, Kevin (2005), "Climate: Uncertainty in Hurricanes and Global Warming, Science, 17 June, vol. 308, no. 5729, pp. 1753–1754.
Hurricanes To Intensify as Earth Warms (June 16, 2005)
Center for Health and Global Environment
Harvard Medical School, Cambridge, Massachusetts
Written statement distributed at news conference
Human activities are changing the composition of the atmosphere and global warming is happening as a result. Global warming is manifested in unexpected ways. Sea level has risen 1.25 inches in the past 10 years as a result of warming of the oceans and glacier melting. The environment in which hurricanes form is changing. The result was a hurricane in late March 2004 in the South Atlantic, off the coast of Brazil: the first and only such hurricane in that region. Several factors go into forming hurricanes and where they track. But the evidence strongly suggests more intense storms and risk of greater flooding events, so that the North Atlantic hurricane season of 2004 may well be a harbinger of the future.
Opening statement excerpts
Global sea level has risen about an inch and a quarter in the past 10 years. This is good information—the first time we've had global information from satellites using a process called altimetry. Now most of this rise in sea level is due to expansion of the ocean as it warms up, and maybe 20 to 35% is from melting of glaciers. So the sea surface temperature is rising globally. It's been about 1 degree Fahrenheit over the 20th century and it's risen in particular in recent times in the Atlantic and other regions, of course, that affect hurricanes.
. . .
And of course this is the fuel for the hurricanes and it also means that the hurricanes end up dropping a lot more precipitation and rainfall as a result. And so the environment in which these hurricanes form is changing and it's changing in ways that provide more fuel for them through the water vapor and the changes in sea surface temperature.
. . .
What we can say is that the high sea surface temperatures of water vapor make for more intense storms, and so this is consistent with the evidence that we're seeing. And so this is the main link with global warming that we can establish at the current time.
And so this is supported also by the modeling evidence and the theoretical evidence. There was a certain amount of activity regarding a paper that came out recently by a group headed by Tom Knutson at the Geophysical Fluid Dynamics Laboratory—laboratory for those of you, if I say it in American. And that supports the idea that indeed hurricanes are apt to become more intense in the future. So a key consequence, I think, is certainly perhaps increased damage from winds, but I think the biggest consequence is likely to be more heavy rains and flooding.
Other news conference participants
Backgrounder: Hurricanes, Typhoons, and Cyclones