November 9, 2006

Not Quiet on the Hurricane Front

Filed under: Climate Extremes, Hurricanes

As the very quiet hurricane season of 2006 comes to an end, two very interesting articles have appeared in the peer-reviewed scientific journals on the subject of climate change and hurricane activity. In the most recent issue of the Bulletin of the American Meteorological Society, Philip Klotzbach and William Gray of Colorado State University analyzed the causes of the destructive 2004 hurricane season. In case you have forgotten, Katrina and a number of other large hurricanes were part of the 2005 hurricane season. The 2004 season was also very active, but nearly forgotten given the events of 2005.

Klotzbach and Gray began their article by noting “In the aftermath of the destructive 2004 hurricane season, many individuals queried whether the landfall of four destructive hurricanes in such a short period of time was related to human-induced climate change brought on by increased greenhouse gas emissions. The Center for Health and Global Environment at the Harvard Medical School held a news conference in the wake of the four storms and indicated that humans were likely to be somewhat responsible for these damaging cyclones.” A year before Katrina and 2005, the drums of the global warmers were already beating out their message that hurricanes should be blamed on fossil fuel emissions and the resulting increase in planetary temperature. Gore and others make this theme a centerpiece in their disinformation campaign.

Klotzbach and Gray show that hurricane activity in the Atlantic has increased since 1995, but they reveal that “global tropical-cyclone activity, as measured by the accumulated cyclone energy (ACE) index, has decreased slightly during the past 16 years
(1990–2005).”. But in explaining the unusual 2004 season, they conclude “We attribute the heightened Atlantic major hurricane activity of the 2004 season as well as the increased Atlantic major hurricane activity of the previous nine years to be a consequence of multidecadal fluctuations in the strength of the Atlantic multidecadal mode and strength of the Atlantic Ocean thermohaline circulation.” Sorry, but these two experts did not find global warming to be culprit at all. However, they warn at the end “Due to the increased coastal population and wealth, the U.S. coastline can expect hurricane-spawned damage and destruction in the coming few decades to be on a scale much greater than has occurred in the past.”

The second article is published in the most prestigious Science magazine by Chris Landsea of the NOAA National Hurricane Center, and others, and they raise a very important issue regarding the debate about strengthening hurricanes. Landsea et al. note that “Recent studies have found a large, sudden increase in observed tropical cyclone intensities, linked to warming sea surface temperatures that may be associated with global warming. Yet modeling and theoretical studies suggest only small anthropogenic changes to tropical cyclone intensity several decades into the future [an increase on the order of ~5% near the end of the 21st century].” In their own words, they raise the question “Are the global tropical cyclone databases sufficiently reliable to ascertain long-term trends in tropical cyclone intensity, particularly in the frequency of extreme tropical cyclones”?

The Landsea et al. team notes that “Tropical cyclone intensity is defined by the maximum sustained surface wind, which occurs in the eyewall of a tropical cyclone over an area of just a few dozen square kilometers.” Not so many years ago, aircraft were used to make these critical measurements, but now a fleet of geostationary satellites can provide “higher resolution images and more direct overhead views of tropical cyclones” that “result in greater and more accurate intensity estimates.”. They note that “Therefore, tropical cyclone databases in regions primarily dependent on satellite imagery for monitoring are inhomogeneous and likely to have artificial upward trends in intensity.” They note that “Data from the only two basins that have had regular aircraft reconnaissance—the Atlantic and Northwest Pacific—show that no significant trends exist in tropical cyclone activity when records back to at least 1960 are examined.” In conclusion, Landsea et al. state “that extreme tropical cyclones and overall tropical cyclone activity have globally been flat from 1986 until 2005, despite a sea surface temperature warming of 0.25°C.”

We at World Climate Report marvel at the number of articles that clearly show no link between hurricane activity and global warming, and yet, most folks seem the believe that the hurricane – greenhouse connection is unquestioned in the science community. Just the opposite happens to be the reality.


Klotzbach, P.J. and W.M. Gray. 2006. Causes of the Unusually Destructive 2004 Atlantic Basin Hurricane Season. Bulletin of the American Meteorological Society, 87, 1325-1333.

Landsea, C.W., B.A. Harper, K. Hoarau, J.A. Knaff. 2006. Can We Detect Trends in Extreme Tropical Cyclones? Science, 313, 452-454.

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