Hurricanes and Global Warming:
Expectations versus
Observations
21 April, 2006
University of Miami
Chris Landsea
National Hurricane Center, Miami
Outline
•Why have hurricane damages gone way up?
•How have hurricanes changed in the past?
•What environmental factors control hurricanes?
•What may the next couple decades bring?
•What are the projections for global warming
impacting hurricane activity in the future?
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Increases in personal wealth (people have more
“stuff”, and larger homes to stow their stuff, etc.)
has led to greatly increased damage from
hurricanes.
Florida Coastal Population
NORMALIZED DAMAGE is estimated
economic damages if past storms made
landfall with present-day societal
conditions.
ND = f(inflation, population, wealth)
Source:
Pielke, Jr., R. A., and C. W. Landsea, 1998: Normalized Hurricane Damages in the
United States: 1925-1995. Weather and Forecasting, 13:351-361.
2005:
27
Aircraft Reconnaissance: 1960
WB-50
Superfortress
-March 18, 1960: discont’d for
1 ½ yrs
-range: 5,850 mi, 10-20 hr
-ceiling: 45,000 ft
height finding radar
WCN-121
Super Constellation (6)
-flight crew: 22-28
-range: 4,250 mi, 16-18 hr
-ceiling: 25,000 ft
long range search radar
2005:
1–
Wilma
Hurricane Mitch Near Peak Intensity
Atlantic Multidecadal Mode
Local Correlation of SST versus REOF
Mestas-Nunez and Enfield (1999)
2005:
+0.25
2005:
+0.7
Coverage of Low Tropospheric Vertical Wind Shear
U.S. MAJOR LANDFALLING HURRICANES:
1903-2000
Major
East Coast
Hurricanes
Inactive Decades
Active Decades
Caribbean Hurricanes –
Atlantic Multidecadal Mode
Global Warming –
Past Temperature
Changes
SST changes
2 x CO2
Sea Surface Temperatures – 26.5C Threshold
SST and Tropical Cyclogenesis Changes
Henderson-Sellers et al. (1998)
Global Warming
– Changes in
Tropical Cyclone
Frequency
Royer et al. (1998)
Tropical Cyclone
Intensity Changes
from Global
Warming –
Use of
Mesoscale Models
Comparison of
4 convection
schemes and
9 coupled
global models Knutson and Tuleya (2004)
Global Warming – Radiative Forcing Scenario
“The rate of radiative forcing increase implied by 1% per year increasing CO2 is nearly
a factor of two greater than the actual anthropogenic forcing in recent decades, even if
non-CO2 greenhouse gases are added in as part of an ‘equivalent CO2 forcing’ and
anthropogenic aerosols are ignored (see, e.g., Figure 3 of Hansen et al. 1997). Thus the
CMIP2 increasing-CO2 scenario cannot be considered as realistic for purposes of
comparing model-predicted and observed climate changes during the past century. It is
also not a good estimate of future anthropogenic climate forcing, except perhaps as an
extreme case in which the world accelerates its consumption of fossil fuels while
reducing its production of anthropogenic aerosols.” – Covey et al. (2003)
Global Warming and Hurricane Winds:
Theory and Modeling Work Suggest 5% increase by late 21st Century
Knutson & Tuleya (2004)
Global Warming and Hurricane Winds:
Theory and Modeling Work Suggest ~1% Increase Today
Global Warming and Hurricane Winds:
Theory and Modeling Work Suggest ~1% Increase Today
1-2 mph of Katrina’s 170 mph
“An important issue is whether and when any CO2induced increase of tropical cyclone intensity is likely to
be detectable in the observations. The magnitude of the
simulated increase in our experiments is about +6% for
maximum tropical cyclone surface winds … The SST
changes observed for the past 50 yr in the Tropics imply
that the likely SST-inferred intensity change for the past
half century is small, relative to both the limited
accuracy of historical records of storm intensity and to
the apparently large magnitude of interannual variability
of storm intensities in some basins. This further implies
that CO2-induced tropical cyclone intensity changes are
unlikely to be detectable in historical observations and
will probably not be detectable for decades to come.”
--- Knutson and Tuleya (2004)
Emanuel’s study:
Doubling in Atlantic Hurricane Wind Index – “Unprecedented”
PDI = Power
Dissipation
Index (winds
cubed &
summed for
season)
Emanuel (2005)
“P. Webster (EAS, GT), Greg
Holland (NCAR), Judy Curry
(EAS, GT) and Hai-Ru Chang
(EAS, GT) reports in Science that
the number of Category 4 and 5
hurricanes has nearly doubled
over the past 35 years.” (Authors’
Webpage)
A 5% overall intensity
increase would lead to a
25% increase in # of
Category 4&5 hurricanes
late in the 21st Century.
The Dvorak Technique (1972)
Infrared Version of Dvorak (1984)
Coverage Today of Meteorological/Oceanographic Satellites
P. Webster (EAS, GT), Greg
Holland (NCAR), Judy Curry
(EAS, GT) and Hai-Ru Chang
(EAS, GT) reports in Science that
the number of Category 4 and 5
hurricanes has nearly doubled
over the past 35 years.
Previously unrecognized
Category 4 and 5 TCs in the
North Indian Ocean – 1978-1989
Atlantic Hurricane Database Re-Analysis Project
http://www.aoml.noaa.gov/hrd/data_sub/re_anal.html
1851 through 1914 changes accepted and officially
adopted by NHC. 1915 through 1930 have been
submitted to NHC. Remainder of 20th Century
currently being reanalyzed.
RE-ANALYSES NEED TO BE CONDUCTED
GLOBALLY!!!
"Florida's Hurricane History"
Effects of Anthropogenic Global Warming
On Tropical Cyclones
Frequency? +/-10%
Maximum intensity? +5%
Average intensity? +5%
Rainfall? +5%
Area of formation/occurrence? No change
Size? ???
Global Warming versus Society Changes:
Hurricane Damages
Outline
•Why have hurricane damages gone way up?
•How have hurricanes changed in the past?
•What environmental factors control hurricanes?
•What may the next couple decades bring?
•What are the projections for global warming
impacting hurricane activity in the future?
Atlantic SST versus Major Hurricane Activity
GFDL Model Intensity Forecast Ability
Normalized Error (%)
2003 ATLANTIC INTENSITY ERRORS (early)
50
40
30
20
10
0
-10
-20
-30
-40
OFCL
SHIP
DSHP
GFDI
GFSI
12
24
36
48
(281) (266) (236) (200)
72
96
120
(152)
(121)
(100)
Forecast Period (hr)
(number of cases)
Gross (2003)
TRMM-based
Tropical Cyclone
Rainfall –
Lonfat et al. (2004)
TRMM-based Hurricane Rainfall Distribution
GFDL Model Rainfall Forecast Ability
0-100 km
Rogers et al. (2005)
Northwest Pacific
Typhoons Chan and Liu (2004)
SSTs versus
Typhoon Activity
Dvorak Technique Cloud
Patterns
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Global Warming Changes???
Global Warming –
Changes to
Vertical Wind Shear
Georgia-New England Major Hurricanes
1851-2004
Excludes Florida & Gulf Coast because statistics are
unreliable for that state prior to early 20th century
“Can one detect an actual increase in global
tropical cyclone Intensity? … Since 1950 … one
would expect to have observed an average
increase in intensity of around 0.5 m/s or 1 knot.
Because tropical cyclone maximum wind
speeds are only reported at 5-knot intervals and
are not believed to be accurate to better than 5
to 10 knots, and given the large interannual
variability of tropical cyclone activity, such an
increase would not be detectable. Thus any
increase in hurricane intensity that may have
already occurred as a result of global warming
is inconsequential compared to natural
variability.”
--- Kerry Emanuel, 2004
Strong Conveyor
Weak Conveyor