Transcript Increased Atlantic Hurricane Frequency, a Synthesis of Two

Increased Atlantic Hurricane Frequency,
a Synthesis of Two Interpretations
Trent Ford
Hydrology: 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
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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