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  1. Increased Atlantic Hurricane Frequency, a Synthesis of Two Interpretations Trent Ford Hydrology: GEO 361 February 23, 2011

  2. Hurricane Formation • Thunderstorm development West Africa • Clouds grow due to hot water, air; spin due to Coriolis • Warm water fuels storm, hurricane develops • Atlantic Sea Surface Temperatures (SST) and vertical wind shear most important Source: University of Illinois

  3. Source: Holland and Webster 2007

  4. Summary • Hurricane occurrence attributed to anthropogenic-based rise in Atlantic SST (Elsneret al. 2008, Holland and Webster 2007) • Hurricane increase due in part to large scale, multidecadal oscillations marked by variable Atlantic SST • Atlantic Multidecadal Oscillation (Zhang and Delworth 2006) • Atlantic Multidecadal Mode (Goldenberg et al. 2001)

  5. Anthropogenic Climate Change Forcing • Increased GHG buildup increases Atlantic SSTs, leads to rise in ASO hurricane frequency • Warming Atlantic decreases atmospheric stability and deep water circulation (Holland and Webster 2007) • Significant relationship between hurricane frequency and Atlantic SSTs over the past 20 years

  6. Global mean near-surface air temperature (GT) and North Atlantic SST anomalies. The AMO anomalies are in blue. (a) Time series of ASO averaged values of SST GT (b) Scatter plot of GT and SST (c) Scatter plot of SST and the cube root of hurricane frequency Source: Elsner 2006

  7. Anthropogenic Forcing Cont. • Accumulated Cylcone Energy (ACE) index in accordance with statistical model, found tropical Atlantic SST associated with 40% increase in hurricane frequency (Saunders and Lea 2008) • 1º C increase SST increase results in storm wind velocity gain of 2-5m/s (Elsneret al. 2008 Figure 4. Analysis and model results of satellite-derived tropical cyclone lifetime-maximum wind speeds (a) Box plots by year. Trend lines are shownfor the median, 0.75 quantile, and 1.5 times the interquartile range: Elsner et al. 2008

  8. Long-Term Temperature Trend • Long term (>100 yr) data lacking • Current period of increased hurricane activity (16 yr), momentary amount of time in climate science • SST anomalies due to multidecadal oscillations • Vertical shear reductions during positive phase of AMO, increases in negative phase

  9. Source: Goldenberg et al. 2001

  10. Data Issues • Availability is major obstruction for conclusion • Null hypothesis: no trend in hurricane activity; no necessarily accurate • Anthropogenic SST warming reasonable, not confirmed • Oscillation argument based on SST warming phases, seemingly evident for warming climate increase

  11. Number of tropical storms (blue), intense hurricanes (red), ACE index (purple), Linear regression fits for 95% ci for ACE index fit (dashed lines) Source: Saunders and Lea 2008

  12. Conclusion • More research, data needed • SST warming/cooling regimes operate 20-30 years, multi-decade warming evidence for anthropogenic warming • Dangerous game to accept or reject hypothesis without significant evidence

  13. Works Cited • Elsner, James B. “Evidence in support of the climate change-Atlantic hurricane hypothesis” Geophysical Research Letters 33 (2006): 1-3. Web 24 Jan. 2011. • Elsner, James. B., James P. Kossin, and Thomas H. Jagger. “The increasing intensity of the strongest tropical cyclones.” Nature 455 (2008): 92-95. Web. 24 Jan. 2011. • Goldenberg, Stanley B., Christopher W. Landsea, Alberto. M. Mestas-Nunez, and William. M. Gray. “The recent increase in atlantic hurricane activity causes and implications” Science 293 (2001): 474-479. Web. 24 Jan. 2011. • Hurricanes: online meteorological guide. University of Illinois Champaign-Urbana, 1999. Web. 9. Feb. 2011. • Holland, Greg. J., and Peter J. Webster. “Heightened tropical cyclone activity in the north atlantic: natural variability or climate trend?” Philosophical Transactions of The Royal Society 365 (2007): 2695-2716. Web. 20 Jan 2011. • Saunders, Mark A., and Adam S. Lea. “Large contribution of sea surface warming to recent increase in Atlantic hurricane activity.”. Nature. 451 (2008): 557-561. Web. 24 Jan. 2011. • Zhang, Rong, and Thomas L. Delworth. “Impact of atlanticmultidecadal oscillations on india/sahel rainfall and atlantic hurricanes.” Geophysical Research Letters 33 (2006): 1-5. Web. 21 Jan. 2011