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Tropical cyclones and climate

Tropical cyclones and climate. Adam Sobel CEI Katrina workshop. Big Questions from this year. What made this Atlantic hurricane season so hyperactive? Is it natural variability, or a secular trend due to global warming? Are we going to see more and more of these disasters in the future?.

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Tropical cyclones and climate

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  1. Tropical cyclones and climate Adam Sobel CEI Katrina workshop

  2. Big Questions from this year • What made this Atlantic hurricane season so hyperactive? • Is it natural variability, or a secular trend due to global warming? • Are we going to see more and more of these disasters in the future?

  3. 2 splashy papers came out this summer Emanuel 2005, Nature. This picture is for the N. Atlantic; W. Pacific shows same trend Webster et al. 2005, Science.

  4. Total global number of storms of >= TS intensity is not increasing Webster et al. 2005

  5. But the Atlantic has indeed been hopping Now up to 24; this plot made 10/12/05 + Figure courtesy of Suzana Camargo, IRI; data from NOAA

  6. Some caveats on the “observations” of TC intensity • Most storms, most of the time, are not being observed in situ. • Since 1970, we have satellite data, but the methods of inferring intensity from that are empirical and imperfect. • Before 1970, we have no satellite data, and things become still more uncertain. • The transition at 1970 makes the error characteristics discontinuous, so longer-term trends are particularly hard to ascertain.

  7. Physics of climate influence on TCs • We have a theory for the potential intensity (i.e. maximum possible) a TC can reach, given a few environmental variables (e.g. SST) • Combined with climate change predictions, this implies an increase in this maximum intensity. • But most storms don’t reach or even come very close to their potential intensity, and we don’t understand very well what controls how close they come to it. • We don’t understand the genesis of TC’s very well, and so have no theory for their number (though have some small skill in predicting interannual variations using empirical statistical models). Emanuel 1991

  8. The theory under-predicts the observed increase in intensity • Assuming the distribution of TC intensity normalized by potential intensity stays constant gives a prediction of actual intensity increase for the climate warming observed • This is considerably less than found in the recent studies • There is large natural variability on decadal + time scales • All things considered it is far from clear that the observed trend is in any large part due to climate change

  9. There is a large upward trend in damage, but it is almost all due to increasing coastal development Pielke and Sarewitz 2005

  10. US Landfalling Hurricanes, 1851-2004 from C. Landsea’s Tropical Cyclone FAQ http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html

  11. If you are interested in learning more, come to our workshop • Workshop on Tropical Cyclones and Climate • At IRI (Lamont Campus), March 26-28, 2006 • Organized by Suzana Camargo, AHS, and others • Sponsored by ADVANCE, IRI, IGERT

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