Interdepartmental Hurricane Conference

1. Interdepartmental Hurricane Conference A BASC/Personal Perspective Research Bob Serafin March, 2006

2. Hurricane Impacts and Hurricane Characteristics? • More lives and property in vulnerable areas, but… • Much of property built to higher standards over time, safer • Forecasts have been improving, thereby reducing loss of lives and damage • Catastrophic hurricanes relatively rare events-trends of rare events difficult to determine • Hurricane impacts depend on much more than intensity and frequency-high stochastic component related to exact location of landfall, timing, etc. Anthes, Nov. 2005 Talk

3. Therefore….. • Trends in hurricane impacts (loss of life, damage) are not a good indicator of trends in hurricane characteristics such as intensity, size, frequency, rainfall, maximum wind speed, storm surge…

4. Hurricane formation favored by • High ocean temperatures (>26ºC) and heat content (Palmén, 1948; Riehl, 1954) • Preexisting cyclonic disturbances • Low vertical wind shear • High absolute vorticity in lower troposphere • Low static stability (large conditional instability-high sfc θe) • Moist environment Gray, 1968, 1979; Anthes, 1982

5. Hurricane formation in each basin is dependent upon large-scale atmospheric circulation patterns • ENSO (e.g. in El Nino years, hurricane formation is favored in western North Pacific and disfavored in North Atlantic. • QBO • AMO (Atlantic Multidecadal Oscillation) • NAO (North Atlantic Oscillation) • Etc.

6. Outlook • The evidence is strong that barring surprises, the atmosphere and oceans will continue to warm over the next 50 years and the atmospheric water vapor content will continue to increase. • Changes in other factors that are important are less certain, and likely vary from basin to basin. Anthes, Nov.2005 talk

7. Summary • Global Tropical Cyclone Intensity has increased steadily since 1975: • Data, Variability, Climatic Trend; • North Atlantic cyclones have increased, especially in July: • Warmer SSTs, Wave Accumulation Processes; • Next stage: high resolution modeling studies to address causality. Holland, Nov. 2005

8. Index of hurricane destructive power at U.S. landfall shows no systematic trendEmanuel, Nov. 2005 Talk

9. Summary • Global tropical cyclone frequency shows no long-term trend • A measure of total hurricane power generation shows a profound upward trend in the past 30 years, well correlated with SST in key cyclone regions. This is probably owing to global warming, and is a reflection both of increasing intensity and increasing duration. Emanuel, Nov. 2005 Talk

10. Conclusions 1 of 2 “Looking to the future, until scientists conclude (a) that there will be changes to storms that are significantly larger than observed in the past, (b) that such changes are correlated to measures of societal impact, and (c) that the effects of such changes are significant in the context of inexorable growth in population and property at risk, then it is reasonable to conclude that the significance of any connection of human- caused climate change to hurricane impacts necessarily has been and will continue to be exceedingly small.” Pielke et al. 2005

11. Conclusions 2 of 2 “But a great irony here is that invoking the modulation of future hurricanes to justify energy policies to mitigate climate change may prove counterproductive. Not only does this provide a great opening for criticism of the underlying scientific reasoning, it leads to advocacy of policies that simply will not be effective with respect to addressing future hurricane impacts. There are much, much better ways to deal with the threat of hurricanes than with energy policies (e.g., Pielke and Pielke 1997). There are also much, much better ways to justify climate mitigation policies than with hurricanes (e.g., Rayner 2004).” Pielke et al. 2005

12. Some Research Questions • What is the natural variability of the intensity of hurricanes? • What is the natural variability of the frequency of hurricanes? • How much of the variability is stochastic? • Is the apparent recent increase in hurricane intensity natural, anthropogenic, or both? • How should society prepare better for the threat?