Hurricane Katrina and the global warming science: more muddled OR settled?

Madhav Khandekar, AMS Member
52 Montrose Crescent
Unionville, ON, L3R 7Z5

file posted 18 May 2006
text from CCNet,

The devastating impact of hurricane Katrina (August 29/30, 2005) on the great city of New Orleans has once again rekindled the global warming debate with environmentalists, science writers and policymakers churning out opinions and words of wisdom  in various news and print media. A blame game is in full swing with 'global warming' as the primary suspect while among  other 'culprits' are the countries which refuse to sign on to the Kyoto accord to curb greenhouse gas (GHG) emission and a number of climate skeptics who have been arguing against the global warming science.

The debate has been further fueled by the recent publication of two papers in high-profile scientific journals, Nature in UK and Science in USA. These papers are authored by renowned scientists, Kerry Immanuel of MIT (Massachusetts Institute of Technology, USA) and Peter Webster and co-workers at the Georgia Institute of Technology (Atlanta, USA) Both these papers document the strengthening of hurricanes and tropical cyclones in recent years due to warmer waters and in particular to warmer waters of the Atlantic Ocean where a large number of hurricanes have spawned this season. A recent paper  in the AMS Bulletin (Pielke,Jr et al 2005) suggests that hurricanes in the Atlantic have followed a decadal pattern showing no link to global warming. In an informal interview, Prof. William Gray (Colorado State University) who has studied hurricanes for over 50 years categorically dismisses recent hurricane activity in the Atlantic due to global warming, while Prof. James O'Brian (Florida State University) points out that the region of the Atlantic between Africa and the US east coast where hurricanes form and grow does not show any increase in SST (Sea Surface Temperature) in recent years.

With so many differing viewpoints, there is a need to closely examine some of the issues re: the global warming science:

1. Global warming & hurricanes: The studies by Immanuel and Webster et al have re-iterated what most students of hurricanes and tropical meteorology have known namely that warmer waters of the oceans ( warmer than 27C) will help hurricanes to grow and strengthen. What is not clear at present is why hurricanes or tropical cyclones do not grow or strengthen equally in different ocean basins? The Bay of Bengal in North Indian Ocean, notorious for some of the deadliest tropical cyclones in the seventies, has seen very few intense tropical cyclones in last ten years. It may be noted that the SSTs in the Bay of Bengal are among the highest anywhere, about 29C. Many other issues re: hurricane strength and its relation to vertical tilt of the hurricane axis, vertical wind shear and the strength of the upper tropospheric outflow are not fully resolved at this time. .Also, it is not completely understood whether recent warming of ocean surface waters is all due to human-added CO2 or due to factors  like cloud cover changes in tropical latitudes , solar variability etc.

2. Global warming & extreme weather: The IPCC (Intergovernmental Panel on Climate Change) Climate Change Document 2001 lists a number of extreme weather events ( e.g., heat waves, extreme precipitation, increased summer continental drying and risk of droughts) which are likely to increase as a result of global warming. A detailed analysis of such events for Canada (Khandekar, 2002) and for USA (Balling & Cerveny, 2003) does not support IPCC conclusion at this point in time. Elsewhere, extreme weather events do not show any consistent pattern (increase/decrease) to support IPCC hypothesis of increase in extreme weather events. As Khandekar et al (2005) have summarized Global warming and extreme weather link is more a perception than reality.

3. Global warming & escalating economic impact: Changnon and co-workers have shown in several excellent papers (e.g, Changnon, 2003: Changnon et al, 2000) that Shifting economic impacts from weather extremes in the USA is a result of societal change and not global warming. Elsewhere, very few detailed studies are available to make a definitive assessment.

4. Global warming & sea level rise: IPCC Climate Change documents (1996, 2001) have discussed the possibility of accelerated sea level rise leading to flooding of low-lying islands like the Maldives in the Indian Ocean and Tuwalu Island in south Pacific. Several studies have now shown that there has not been accelerated sea-level rise anywhere in the 20th century. The Maldive islands sea level variation has been extensively studied by Morner (2003) among others and the 'threat' of the islands being inundated in next fifty to one hundred years has been discounted.

5. Global warming & Arctic 'melt-down' and sea-ice reduction: The Arctic is a complex atmosphere-ocean-ice climate system whose variability is not fully understood. According to several recent studies (e.g., Polyakov, 2003), the Arctic surface temperature was at its peak during 1935/36, then the temperature started to decline and since about 1970s the Arctic surface temperature has been steadily climbing and is presently at about the same level as it was during the 1930s. Further, Russian data on Arctic weather and climate show a definite increase in winter cloud cover during the late 1970s through most of eighties, this winter cloud cover increase having contributed more to the thinning of Arctic ice than human-added CO2. Another recent paper (Soon 2005) documents high correlation between TSI (Total Solar Irradiance) and Arctic surface air temperatures reconstructed over a long period 1875-2000,while documenting relatively weak correlation with atmospheric carbon dioxide mixing ratio.  

There are several related issues that are being debated in the science and news media. Specifically, the contention by IPCC that the twentieth century has been the warmest in the last 2 millennium has been challenged in several recent studies and the debate continues at present. Also, the magnitude of the observed warming is another issue being debated. So far, there is no evidence of a catastrophic warming. The observed warming appears to be modest and recent projections suggest a warming of only about 1C or so in next 50 to 75 years.

Has the recent debate helped settle the global warming science or has it become more muddled? The global warming advocates seem to think that it is settled in their favor. Most climate skeptics would like to think that the science is far from settled and needs to be reassessed.

I believe it is time to debate the science openly in scientific journals and magazines.


Balling, R. C. and R. S. Cerveny, 2003: Compilation and discussion of trends in severe storms in the United States: Popular perception vs. climate reality.  Natural Hazards, 29, 103-112.

Changnon, S. A., 2003: Shifting economic impacts from weather extreme in the United States: A result of societal changes, not global warming. Natural Hazards, 29, 273-290

"                et al, 2000: Trends in socio-economic impacts related to weather and climate extremes in the USA. Bull. Amer. Met Soc. 81, 437-442

Khandekar, M L 2002: Trends and Changes in extreme weather events: An assessment with focus on Alberta and Canadian Prairies. Rept. Prepared for Alberta Environment, ISBN:0-7785-2428-0, October 2002, 56 p. (

"                , T S Murty and P. Chittibabu, 2005: The global warming debate: a review of the state of science. Pure & Applied Geophysics, 162, 1557-1586.

Morner, N, M Tooley and G Possnert, 2004: New perspectives for the future of the Maldives. Global and Planetary Change, 40, 177-182

Pielke, Jr R A, C Landsea, M Mayfield, J Laver and R Pasch 2005: Hurricanes and global warming. Bulletin, AMS, 86,No.11, p.1571-1575.

Polyakov I. et al, 2003: Variability and trends of air temperature and pressure in the maritime Arctic, 1875-2000. J of Climate, 16, 2067-2077

Soon,W-H Willie 2005: Variable solar irradiance as a plausible agent for multidecadal variations in the Arctic-wide surface air temperature record of the past 130 years. Geophy. Res. Letters, 32, L16712, August 2005