From Kansas State University's:

Consortium for Agricultural Soils Mitigation of Greenhouse Gases(CASMGS)


Charles W. Rice, K-State Department of Agronomy, National CASMGS Director

(785) 532-7217

Scott Staggenborg, K-State Department of Agronomy (785) 532-7214

Steve Watson, CASMGS Communications (785) 532-7105


September 21, 2005

No. 47



* Global Warming And Hurricane Intensity

* Reaction To The “Global Warming-Hurricane” Research






Global Warming and

Hurricane Intensity


You may have heard or read over the past week or so about a possible link between global warming and hurricane activity. What are the facts behind the news stories? Most of the “buzz” was created by one research study by an MIT climatologist published recently in the journal Nature. But that’s only one of at least four recently published studies have addressed this issue.


There are two main conclusions from these studies at this point:


1. None of the studies contends that global warming has caused an increase in the number of hurricanes.


2. There is, however, evidence that global warming may be causing an increase in the destructive power of hurricanes over the past 30-35 years.


The second conclusion has come as something of a surprise to scientists. Before these recent studies, most researchers believed global warming's contribution to powerful hurricanes was too slight to accurately measure. Most forecasts had not shown climate change making a real difference in tropical storms until 2050 or later. But the more recent studies indicate that these forecasts may have been wrong, and the effect has already occurred.


Hurricane intensity and duration can be directly correlated with warmer surface sea temperatures, among many other factors. Pools of warming seawater provide energy for storms as they develop over the open oceans, especially in the Atlantic and Caribbean basins. Global warming is one cause, perhaps the main cause, of the increase in surface sea temperatures. Therefore, it’s not surprising that theories and computer simulations indicate that global warming should eventually generate an increase in storm intensity.


The main questions have always been whether other factors are more important in determining storm intensity than surface sea temperatures, and how long it would take before the warmer temperatures would begin affecting hurricane activity.


Those questions do not yet have definitive answers, although the evidence is now swinging toward the two conclusions listed above. No one, including the authors of the papers described below, is claiming that the research so far fingers global warming as the only culprit in hurricane intensification. There are other factors involved, such as vertical wind shear activity, upper level high pressure ridges, El Nino effects, and other factors. Global warming, through its effect on warmer surface sea temperatures, does appear to be an important factor, however.


Those scientists who dispute these conclusions generally have two arguments. The first is that there’s no conclusive evidence that hurricane intensity has actually been increasing over the past 30-35 years. The second is that hurricane intensity is determined by many factors, and the warmer surface sea temperature is just one of these factors – maybe not even the most important factor.


It’s important to keep things in perspective. None of the scientists who believe that global warming has already caused an increase in hurricane intensity is blaming anyone for the recent disaster. They are just presenting the evidence, making their best judgment on how to interpret the evidence, and pointing out one of the possible implications of global warming if nothing is done about it. The beneficial effect of a reduction in global warming on hurricane intensity would be gradual, not immediate, and may not be evident for many years. Other measures will have to be taken in the near-term to mitigate the impact of high-intensity hurricanes on lives and property.  


In any case, here is a short summary of each of the four published studies, along with a link to each of them.


A. The first, and most widely publicized, study made national news because of the uncanny timing of its publication in the August 4, 2005 issue of the prestigious journal Nature – shortly before Hurricane Katrina.


The author of this study is climatologist Kerry Emanuel of the Massachusetts Institute of Technology. Emanuel has been publishing on the link between hurricane intensity and climate since the mid-1908s.


Emanuel calculated the total potential destructive power over the life of all storms each year since about 1950 in the North Atlantic and the northwest Pacific. He found that since the mid-1970s, hurricanes have increased in duration and top sustained wind speed. This increase in destructive power is highly correlated with higher surface temperature of tropical seas, according to his study. The increase in storm wind speed has been 70 to 80 percent, and the increase in duration has been about 50 percent.


Previous computer models had predicted that the one-degree (Fahrenheit) increase in sea-surface temperatures from global warming over the past 30 years should have increased wind speed by only about 3 percent, corresponding to a 10 percent increase in destructive power. So the actual measured increase in destructive power was much higher than predicted.


Those who study tropical ocean temperatures believe that this recent upward trend in ocean surface temperatures is mostly a consequence of global warming, Emanuel says. Part of the increase is also due to natural long-term changes in temperatures and salinity within the deep currents of the North Atlantic and North Pacific oceans.


“My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential, and -- taking into account an increasing coastal population -- a substantial increase in hurricane-related losses in the twenty-first century,” he concludes.


You can read the full text of Emanuel’s Nature article at:


An interview with Emanuel, from “Living on Earth,” can be found at:



B. An even more recent study was just published in the September 16, 2005 issue of Science. The lead author is Peter Webster, with the School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta.


This research evaluated the number and intensity of hurricanes over the past 35 years in the North Pacific, Indian, Southwest Pacific, and North Atlantic Oceans, and correlated that with changes in surface sea temperatures. Although Webster’s team found no increase in the overall number of hurricanes from the first half to the second half of that period, there has been a significant increase (57 percent) in the number of category 4 and 5 hurricanes.


“We conclude that global data indicate a 30-year trend toward more ... intense hurricanes, corroborated by the results of the recent regional assessment. This trend is (consistent) with recent climate model simulations that a doubling of CO2 may increase the frequency of the most intense cyclones, although attribution of the 30-year trends to global warming would require a longer global data record and, especially, a deeper understanding of the role of hurricanes in the general circulation of the atmosphere and ocean, even in the present climate state.”



Webster’s article can be found at:



C. The third study was published in the June 17, 2005 issue of Science. The author is Kevin Trenberth, of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado.


In this study, Trenberth correlated sea surface temperatures with hurricane activity, and came to conclusions similar to Emanuel’s. Trenberth notes that many factors affect hurricane activity in addition to sea surface temperatures – such as conditions in the upper troposphere; vertical wind shear activity; easterly lower atmospheric winds from the African coast; the presence of El Nino events; and general atmospheric stability.


He concludes that global warming and other causes of increased sea surface temperatures cannot be proven to have any effect on the number of hurricanes that develop. But it is probably having an effect on hurricane intensity.


“Trends in human-influenced environmental changes are now evident in hurricane regions. These changes are expected to affect hurricane intensity and rainfall, but the effect on hurricane numbers remains unclear . . . Model results suggest a shift in hurricane intensities toward extreme hurricanes,” Trenberth states.


Trenberth’s article in Science can be found at:



D. The fourth study was published in the September 15, 2004 issue of the Journal of Climate. The principal author is Thomas Knutson, with the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton, NJ.


In this study, the authors did a large-scale computer simulation using nine different global climate models and four different versions of the new high-resolution GFDL hurricane model to see what the effects of warmer temperatures due to increased CO2 levels in the atmosphere would have on hurricane activity. The actual study is quite detailed, but the main conclusion is:


“If the frequency of tropical cyclones remains the same over the coming century, a greenhouse-gas induced warming may lead to a gradually increasing risk in the occurrence of highly destructive category-5 storms.”


The article can be found at:


A summary of the research, from NOAA’s GFDL office, concludes that:


“The strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases in the atmosphere. Although we cannot say at present whether more or fewer hurricane will occur in the future with global warming, the hurricanes that do occur near the end of the 21st century are expected to be stronger and have significantly more intense rainfall than under present day climate conditions.”


The complete summary (which is quite short) can be found at:



-- Steve Watson






Reaction To The

“Global Warming-Hurricane” research



Most scientists in the climate field are taking seriously the possible link between global warming, surface sea temperatures, and current hurricane intensity. Despite some differences in research methods and objectives, the conclusions of the four research papers described in the article above are in general agreement about the possible link between global warming, warmer surface sea temperatures, and hurricane intensity.


Still, not everyone agrees, which is not surprising in the scientific world. An objective analysis of the pros and cons of Emanuel’s research can be found in New Scientist:


This article in New Scientist mentions some of the research that supports the proposed link between global warming and hurricane intensity. This article also mentions some opposing arguments. For example, it points out that measuring hurricane wind speeds is not an exact science, and that there are some questions about Kerry Emanuel’s method of adjusting the estimated wind speed of hurricanes in the 1950’s and 1960’s. If the adjusted wind speeds Emanuel used for these decades was too low, then his conclusions may not be accurate.

Researchers are now using new methods to analyze early storms, going back to the 1800’s, that were not included in the analyses used for the most recent studies. If those early storms turn out to be more powerful than originally thought, the premise that hurricane intensity has been increasing in recent years might not hold up, say some scientists.


Other scientists, such as Christopher Landsea, a research meteorologist now with NOAA’s Atlantic Oceanographic & Meteorological Laboratory in Miami, simply don’t think there’s enough accuracy yet in models that try to link oceanic and atmospheric events to make any conclusions one way or another. For example, see:

An interesting, although long and rambling, discussion of the “global warming-hurricane” relationship can be found on the RealClimate web site. This site includes a short article, basically discussing the points mentioned above, followed by a comment section with a wide variety of informed and uninformed opinions:


The insurance industry has taken note of Emanuel’s research linking global warming to increasing hurricane destructive power. An article on Emanuel’s research appeared in the August 1, 2005 issue of Insurance Journal:


Overall, the research linking global warming with an increase in the destructive power of hurricanes has considerable scientific credence. Further research will add to our understanding of this possible link, but for now the evidence presented by Kerry Emanuel and the others adds one more reason to take action to reduce global warming.


-- Steve Watson






UPCOMING CONFERENCES (all dates are 2005 unless otherwise noted)


September 26-30

7th International CO2 Conference

Broomfield, CO

For more information:



November 13-17

Greenhouse 2005: Action on Climate Control

Melbourne, Australia

For more information: 

Contact: Paul Holper



January 22-25, 2006

9th Annual Electric Utilities Environmental Conference

Impending Carbon Regulations, Impacts, and Mitigation Strategies

Tucson, AZ

For more information:






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