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 - and the 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 are in agreement with the consensus statement issued by the International Workshop on Tropical Cyclones held in Costa Rica at the end of 2006. The statement was written by 125 tropical meteorologist from some 34 countries 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 relationship between climate change and tropical cyclones (including hurricanes and typhoons), a new summary statement on the topic has been developed by the global community of tropical cyclone researchers and forecasters as represented at the 6th International Workshop on Tropical Cyclones of the World Meteorological Organization (November 2006). A more comprehensive statement was also developed at the workshop.
The summary statement notes the following: "The surfaces of most tropical oceans have warmed by 0.25-0.5 degree Celsius during the past several decades. The Intergovernmental Panel on Climate Change (IPCC) considers that the likely primary cause of the rise in global mean surface temperature in the past 50 years is the increase in greenhouse gas concentrations....
...Some recent scientific articles have reported a large increase in tropical cyclone energy, numbers, and wind-speeds in some regions during the last few decades in association with warmer sea surface temperatures. Other studies report that changes in observational techniques and instrumentation are responsible for these increases."
Consensus statements by the workshop participants
"1. Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.
2. No individual tropical cyclone can be directly attributed to climate change.
3. The recent increase in societal impact from tropical cyclones has been largely caused by rising concentrations of population and infrastructure in coastal regions.
4. Tropical cyclone wind-speed monitoring has changed dramatically over the last few decades leading to difficulties in determining accurate trends.
5. There is an observed multi-decadal variability of tropical cyclones in some regions whose causes, whether natural, anthropogenic or a combination, are currently being debated. This variability makes detecting any long-term trends in tropical cyclone activity difficult.
6. It is likely that some increase in tropical cyclone peak wind-speed and rainfall will occur if the climate continues to warm. Model studies and theory project a 3-5% increase in wind-speed per degree Celsius increase of tropical sea surface temperatures.
7. There is an inconsistency between the small changes in wind-speed projected by theory and modeling versus large changes reported by some observational studies.
8. Although recent climate model simulations project a decrease or no change in global tropical cyclone numbers in a warmer climate there is low confidence in this projection. In addition, it is unknown how tropical cyclone tracks or areas of impact will change in the future.
9. Large regional variations exist in methods used to monitor tropical cyclones. Also, most regions have no measurements by instrumented aircraft. These significant limitations will continue to make detection of trends difficult.
10. If the projected rise in sea level due to global warming occurs, then the vulnerability to tropical cyclone storm surge flooding would increase."
The full texts of the summary statement and comprehensive statement should be consulted for more details and context."
I also feel strongly about the main hurricane problem facing the United States which can be found at http://wind.mit.edu/~emanuel/Hurricane_threat.htm. It is worth noting the scientists who signed the following statement. This statement is just 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 possible influence of climate change on hurricane activity is receiving renewed attention. While the debate on this issue is of considerable scientific and societal interest and concern, it should in no event detract from the main hurricane problem facing the United States: the ever-growing concentration of population and wealth in vulnerable coastal regions. These demographic trends are setting us up for rapidly increasing human and economic losses from hurricane disasters, especially in this era of heightened activity. Scores of scientists and engineers had warned of the threat to New Orleans long before climate change was seriously considered, and a Katrina-like storm or worse was (and is) inevitable even in a stable climate.
Rapidly escalating hurricane damage in recent decades owes much to government policies that serve to subsidize risk. State regulation of insurance is captive to political pressures that hold down premiums in risky coastal areas at the expense of higher premiums in less risky places. Federal flood insurance programs likewise undercharge property owners in vulnerable areas. Federal disaster policies, while providing obvious humanitarian benefits, also serve to promote risky behavior in the long run.
We are optimistic that continued research will eventually resolve much of the current controversy over the effect of climate change on hurricanes. But the more urgent problem of our lemming-like march to the sea requires immediate and sustained attention. We call upon leaders of government and industry to undertake a comprehensive evaluation of building practices, and insurance, land use, and disaster relief policies that currently serve to promote an ever-increasing vulnerability to hurricanes.
I'm sure this is more from me than you wanted to know. But I want the record to show that no one forced me to say anything on the subject of climate change and tropical cyclones that I didn't believe at the time.