Climate Change & Tropical Cyclones • Current Weather • Tropical Cyclone Review • Broader Context of Tropical Cyclones • Previous Debates in Scientific Literature • Group Activity • For Next Class: Read IPCC AR4 Ch. 4 (pp. 356-367) • Reminder: Exam III on 4 April!
Tropical Cyclones Figure 8.26
North Carolina coast experiences a higher frequency of tropical cyclone activity than anywhere else in the Atlantic basin. Changes in tropical cyclone activity will have a significant impact on North Carolina! Konrad & Perry (2009), Int. J. Clim.
Tropical Cyclone Trends • Are tropical cyclones becoming more frequent? • Are they getting stronger? • Is destructiveness from land-falling tropical cyclones increasing? • Attribution?
Broader Context • “Theory and modeling predict that tropical cyclone intensity should increase with increasing global mean temperatures” (Emanuel 2005) • Record hurricane season of 2004 and Katrina in 2005 contributed to scientific, public, and media interest in the possible connections between anthropogenic warming and tropical cyclone behavior.
Who are Key Players? • Dr. Kerry Emanuel, Massachusetts Institute of Technology (MIT) • Dr. Roger Pielke, Jr., University of Colorado • Dr. Christopher Landsea, NOAA’s National Hurricane Center
Emanuel (2005) • Power Dissipation Index (PDI), a measure of potential destructivenss of tropical cyclones, has increased markedly since the mid-1970s. • PDI is highly correlated with tropical sea-surface temperatures (SSTs). • “Results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential and – taking into account an increasing coastal population – a substantial increase in hurricane-related losses in the twenty-first century.”
PDI (Power Dissipation Index) has increased since 1970s for Atlantic tropical cyclones. Emanuel (2005), Nature
PDI (Power Dissipation Index) has increased since 1970s for Atlantic and W. Pacific tropical cyclones. Emanuel (2005), Nature
Pielke, Jr. (2005) Response • “My analysis of a long-term data set of hurricane losses in the United States shows no upward trend once the data are normalized to remove the effects of societal changes.” • “. . . it is misleading to characterize Emanuel’s results as indicating an increase in ‘destructiveness’ or as an indication of future increases in destruction resulting from changes in the PDI.”
Landsea (2005) Response • “I question his [Emanuel’s] analysis on the following grounds: it does not properly represent the observations described; the use of his Atlantic bias-removal scheme may not be warranted; and further investigation of a substantially longer time series for tropical cyclones affecting the continental United States does not show a tendency for increasing destructiveness.” • “It is difficult to separate out any anthropogenic signal from the substantial natural multidecadal oscillations with a relatively short record of tropical-cyclone activity.” • “. . . claims to connect Atlantic hurricanes with global warming are premature.”
No trend in the PDI of U.S. land-falling tropical cyclones. Landsea (2005), Nature
Hurricane Sandy • Did Anthropogenic Global Warming cause Hurricane Sandy? • http://www.youtube.com/watch?v=YPfAvgJLDyA
Group Activity (Knutson et al. 2010) • Do past changes in any tropical cyclone activity exceed variability expected through natural causes? • How is greenhouse warming likely to influence tropical cyclone activity? • Frequency, intensity, and rainfall • Genesis, tracks, duration, and surge flooding
Knutson et al. (2010) • “We cannot at this time conclusively identify anthropogenic signals in past tropical cyclone data.” • “A substantial human influence on future tropical cyclone activity cannot be ruled out, however, and could arise from several mechanisms (including oceanic warming, sea-level rise, and circulation changes).”