Recent Hurricanes Not Caused by Warming, Scientists Conclude

Published October 1, 2005

The recent devastation by Hurricane Katrina, which made landfall on the Louisiana, Mississippi, and Alabama coastlines on August 29, has brought renewed claims from some environmental activists that global warming is contributing to an increasing number of more severe hurricanes.

The same day Hurricane Katrina hit land, Robert F. Kennedy Jr. wrote in the online blog Huffington Post, “As Hurricane Katrina dismantles Mississippi’s Gulf Coast, it’s worth recalling the central role that Mississippi Governor Haley Barbour played in derailing the Kyoto Protocol …” Kennedy then claimed the “increasing prevalence of destructive hurricanes” is linked to global warming.

Kennedy’s claims are not new. In the midst of 2004’s busy hurricane season–when four named hurricanes made landfall in the United States and caused billions of dollars’ worth of damage–Kevin Trenberth, an Intergovernmental Panel on Climate Change (IPCC) scientist, held a news conference at Harvard University at which he and others linked the outbreaks of intense hurricane activity to global warming.

Other climatologists, however, say hurricane physics, historic data, and ongoing hurricane research offer scant evidence linking human-caused warming to more frequent or more powerful hurricanes.

Warming Minor in Tropics

Physics and data on temperatures show global warming will not increase hurricane numbers or intensity.

Hurricanes are heat engines, with their severity being driven in part by the difference in temperature between the heat source and the heat sink–the smaller the difference, the less severe the storm season. While global warming is likely to cause the oceans to warm modestly in the coming century, air temperatures nearest the equator, where hurricanes form, will see little or no increase.

While the reduced differential between the air and water temperatures alone is likely to be too small to result in fewer or less-powerful hurricanes, it works against more hurricanes of greater intensity forming.

“Really, for the folks that are doing work on hurricanes, there isn’t a debate (about global warming),” Chris Landsea of the National Oceanic and Atmospheric Administration’s hurricane research division in Miami told MSNBC.

Natural Cycle Fuels Storms

At the annual National Hurricane Conference in March 2005, University of Colorado atmospheric scientist Dr. William Gray explained that natural forces–in the form of periodically changing ocean circulation patterns–and not humans are responsible for hurricane cycles, including the cycle of increasing hurricane activity that the world is currently experiencing.

According to Gray, the number of Atlantic hurricanes during the past decade, including 2004’s above-average season, is part of a completely natural and not at all unusual multi-decadal cycle that scientists have monitored for more than 100 years. “You can say for sure that the hurricane-spawned damage to the U.S. in the next quarter-century is going to be much more than it was in the last quarter-century,” Gray said in an interview at the conference.

“We think it’s ocean circulation patterns,” Gray said in the interview. “It’s not human-induced global warming. It’s related mainly, as we see it, to the global ocean conveyor belt circulation.”

For approximately the past 25 years, the United States had experienced a relative lull in hurricane activity. Unfortunately for those living near the coasts, we recently began to come out of that cycle and into an active cycle like the one experienced from approximately 1930 through 1950.

Scientists Fear Politicians

A paper scheduled to be published this fall in the Bulletin of the American Meteorological Society, “Hurricanes and Global Warming,” by six noted tropical cyclone experts, makes three main points regarding hurricanes and human activity:

  • No connection has been established between greenhouse gas emissions and the observed behavior of hurricanes.
  • The scientific consensus is that any future changes in hurricane intensities will likely be small, in the context of observed natural variability.
  • The zeal by some for political reasons to link future hurricanes to global warming threatens both to undermine support for legitimate climate research and to lead to the implementation of policies that will be ineffective in mitigating hurricane impacts.

“It is interesting that a scientific consensus is ignored when it is convenient to the alarmist case,” said Iain Murray, senior fellow at the Competitive Enterprise Institute. “There is a strong consensus among hurricane scientists that global warming is not driving the current stronger hurricane seasons, yet alarmists who do not specialize in hurricane science repeatedly suggest a link and are repeatedly told by hurricane scientists how wrong they are.

“It will be an interesting test of the alarmists’ claims that they are concerned with scientific integrity to see if they continue to make such baseless accusations,” Murray added.

Climatologists Face Bias

Problems stemming from the politicization of global warming have already arisen. In a publicly released “Dear Colleague” letter in January 2005, Chris Landsea, of the National Oceanic and Atmospheric Administration, resigned as an IPCC researcher.

Landsea’s resignation letter stated he felt that in his area of expertise–climate and hurricanes–the IPCC had become too politicized. In particular, he cited the Harvard news conference at which Trenberth linked the severity of the 2004 hurricane season to global warming.

Landsea noted none of the speakers at the Harvard conference cited any new research in the field to support their claims. He went on to point out, “The evidence is quite strong and supported by the most recent credible studies that any impact in the future from global warming upon hurricanes will likely be quite small.”

Similarly, Colorado State University climatologist Roger Pielke resigned his position from the U.S. Climate Change Science Program in August 2005, explaining that science was taking a back seat to alarmist propaganda and political posturing.

Sterling Burnett ([email protected]) is a senior fellow at the National Center for Policy Analysis.

For more information …

Chris Landsea’s resignation from the Intergovernmental Panel on Climate Change was reported in the April 2005 issue of Environment & Climate News, “Climate Scientist Quits IPCC, Blasts Politicized ‘Preconceived Agendas’,”

A report on hurricanes and global warming by Robert C. Balling Jr., “Calmer Weather: The Spin on Greenhouse Hurricanes,” was published in May 1997 by the Competitive Enterprise Institute and is available through PolicyBot™, The Heartland Institute’s free online research database. Point your Web browser to, click on the PolicyBot™ button, and search for document #5630.