Increased Atlantic Hurricane Frequency, a Synthesis of Two Interpretations

Trent FordHydrology: GEO 361 February 23, 2011

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

Source: Holland and Webster 2007

Summary

• Hurricane occurrence attributed to anthropogenic-based rise in Atlantic SST (Elsner et 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)

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

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

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 (Elsner et 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

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

Source: Goldenberg et al. 2001

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

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

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

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 atlantic multidecadal oscillations on india/sahel rainfall and atlantic hurricanes.” Geophysical Research Letters 33 (2006): 1-5. Web. 21 Jan. 2011