I can truthfully say that no one told me at any time what to say in regard to possible impacts of climate change on tropical cyclones.
Please bear in mind that my testimony for the various Congressional Committees was focused primarily on the National Hurricane Center actions during Hurricane Katrina. The NHC is an operational center whose mission is "To save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards." Someone suggested that I should include a statement on the cause of the increased hurricane activity because there was so much interest in this after Katrina. I remember asking for and obtaining input on this topic from staff at the NHC most knowledgeable on the topic. At the time, it was my belief that the increase in hurricane activity since 1995 was primarily due to natural fluctuations/cycles and was "not enhanced substantially by global warming."
I accept the fact that global warming is real. There have been too many papers published by too many scientists in too many countries to argue otherwise. This is a very significant problem. But my area of expertise is in hurricanes. Most meteorologists with knowledge of tropical cyclones think that there will be some impact from global warming on hurricanes. The debate is over how much of an impact. I have always said publicly that I am willing to be convinced by new data. However, I have problems accepting some of the conclusions from some published papers primarily because of the quality of the historical data sets. Please don't forget that most tropical cyclone centers now use satellite imagery to estimate the intensity of tropical cyclones - andthe geostationary satellite did not come into operational use until the mid 1960s. And the objective technique used to estimate tropical cyclone intensity (the Dvorak Technique) using infrared imagery was not published until 1984. In my opinion, there are indeed more stronger tropical cyclones in the historical data bases in all ocean basins due, in large part, to the better technology.
My current thoughts on climate change and tropical cyclones arein agreement with the consensus statement issued by the InternationalWorkshop on Tropical Cyclones held in Costa Rica at the end of 2006.The statement was written by 125 tropical meteorologist from some 34countries if memory serves me correctly, and it can be found online(http://www.gfdl.noaa.gov/~tk/glob_warm_hurr.html):
"Given the high degree of interest in the possible relationshipbetween climate change and tropical cyclones (including hurricanes andtyphoons), a new summary statement on the topic has been developed bythe global community of tropical cyclone researchers and forecasters asrepresented at the 6th International Workshop on Tropical Cyclones ofthe World Meteorological Organization (November 2006). A morecomprehensive statement was also developed at the workshop.
The summary statement notes the following: "The surfaces of mosttropical oceans have warmed by 0.25-0.5 degree Celsius during the pastseveral decades. The Intergovernmental Panel on Climate Change (IPCC)considers that the likely primary cause of the rise in global meansurface temperature in the past 50 years is the increase in greenhousegas concentrations....
...Some recent scientific articles have reported a largeincrease in tropical cyclone energy, numbers, and wind-speeds in someregions during the last few decades in association with warmer seasurface temperatures. Other studies report that changes in observationaltechniques and instrumentation are responsible for these increases."
Consensus statements by the workshop participants
"1. Though there is evidence both for and against the existenceof a detectable anthropogenic signal in the tropical cyclone climaterecord to date, no firm conclusion can be made on this point.
2. No individual tropical cyclone can be directly attributed toclimate change.
3. The recent increase in societal impact from tropical cycloneshas been largely caused by rising concentrations of population andinfrastructure in coastal regions.
4. Tropical cyclone wind-speed monitoring has changeddramatically over the last few decades leading to difficulties indetermining accurate trends.
5. There is an observed multi-decadal variability of tropicalcyclones in some regions whose causes, whether natural, anthropogenic ora combination, are currently being debated. This variability makesdetecting any long-term trends in tropical cyclone activity difficult.
6. It is likely that some increase in tropical cyclone peakwind-speed and rainfall will occur if the climate continues to warm.Model studies and theory project a 3-5% increase in wind-speed perdegree Celsius increase of tropical sea surface temperatures.
7. There is an inconsistency between the small changes inwind-speed projected by theory and modeling versus large changesreported by some observational studies.
8. Although recent climate model simulations project a decreaseor no change in global tropical cyclone numbers in a warmer climatethere is low confidence in this projection. In addition, it is unknownhow tropical cyclone tracks or areas of impact will change in thefuture.
9. Large regional variations exist in methods used to monitortropical cyclones. Also, most regions have no measurements byinstrumented aircraft. These significant limitations will continue tomake detection of trends difficult.
10. If the projected rise in sea level due to global warmingoccurs, then the vulnerability to tropical cyclone storm surge floodingwould increase."
The full texts of the summary statement and comprehensivestatement should be consulted for more details and context."
I also feel strongly about the main hurricane problem facing theUnited States which can be found athttp://wind.mit.edu/~emanuel/Hurricane_threat.htm. It is worth notingthe scientists who signed the following statement. This statement isjust as valid today as when it was written last year.
"Statement on the U.S. Hurricane Problem
July 25th 2006
As the Atlantic hurricane season gets underway, the possibleinfluence of climate change on hurricane activity is receiving renewedattention. While the debate on this issue is of considerable scientificand societal interest and concern, it should in no event detract fromthe main hurricane problem facing the United States: the ever-growingconcentration of population and wealth in vulnerable coastal regions.These demographic trends are setting us up for rapidly increasing humanand economic losses from hurricane disasters, especially in this era ofheightened activity. Scores of scientists and engineers had warned ofthe threat to New Orleans long before climate change was seriouslyconsidered, and a Katrina-like storm or worse was (and is) inevitableeven in a stable climate.
Rapidly escalating hurricane damage in recent decades owes muchto government policies that serve to subsidize risk. State regulation ofinsurance is captive to political pressures that hold down premiums inrisky coastal areas at the expense of higher premiums in less riskyplaces. Federal flood insurance programs likewise undercharge propertyowners in vulnerable areas. Federal disaster policies, while providingobvious humanitarian benefits, also serve to promote risky behavior inthe long run.
We are optimistic that continued research will eventuallyresolve much of the current controversy over the effect of climatechange on hurricanes. But the more urgent problem of our lemming-likemarch to the sea requires immediate and sustained attention. We callupon leaders of government and industry to undertake a comprehensiveevaluation of building practices, and insurance, land use, and disasterrelief policies that currently serve to promote an ever-increasingvulnerability to hurricanes.
I'm sure this is more from me than you wanted to know. But Iwant the record to show that no one forced me to say anything on thesubject of climate change and tropical cyclones that I didn't believe atthe time.