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Dr. Kerry Emanuel explains how Global Warming increased the power of hurricanes. Hurricane Katrina is discussed, with the conclusion that Katrina probably would not have had the power to break the New Orleans levees in a pre-Global Warming world. April 2009 webinar presented by the Southern Allicance for Clean Energy (http://www.cleanenergy.org/) and the Gulf Restoration Network (http://healthygulf.org/) SlideCast by John Atkeison of the Alliance for Affordable Energy. There is a very small amount of phone noise.
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Hurricanes and Global Warming
Hurricanes and Global Warming
Kerry EmanuelMassachusetts Institute of Technology
IssuesIssues
• Effect of climate change on tropical cyclone Effect of climate change on tropical cyclone activityactivity
• Role of tropical cyclones in the climate Role of tropical cyclones in the climate systemsystem
ApproachesApproaches
• The historical recordThe historical record
• PhysicsPhysics
• ModelsModels
The Historical RecordThe Historical Record
Global TC Frequency, 1970-2006Global TC Frequency, 1970-2006
Data Sources: NOAA/TPC and NAVY/JTWC
Better Intensity Metric:Better Intensity Metric:
The Power Dissipation IndexThe Power Dissipation Index
0
3maxPDI V dt
A measure of the total frictional dissipation of kinetic A measure of the total frictional dissipation of kinetic energy in the hurricane boundary layer over the energy in the hurricane boundary layer over the
lifetime of the stormlifetime of the storm
Atlantic Storm Maximum Power DissipationAtlantic Storm Maximum Power Dissipation(Smoothed with a 1-3-4-3-1 filter)
Po
wer
Dis
sip
atio
n In
dex
(P
DI)
Years included: 1870-2006
Data Source: NOAA/TPC
Atlantic Sea Surface Temperatures and Atlantic Sea Surface Temperatures and Storm Max Power DissipationStorm Max Power Dissipation
(Smoothed with a 1-3-4-3-1 filter)
Sca
led
Tem
per
atu
re
Po
wer
Dis
sip
atio
n In
dex
(P
DI)
Years included: 1870-2006
Data Sources: NOAA/TPC, UKMO/HADSST1
10-year Running Average of Aug-Oct NH Surface T and 10-year Running Average of Aug-Oct NH Surface T and MDR SSTMDR SST
Tropical Atlantic SST(blue), Global Mean Surface Tropical Atlantic SST(blue), Global Mean Surface Temperature (red), Temperature (red),
Aerosol Forcing (aqua)Aerosol Forcing (aqua)
Mann, M. E., and K. A. Emanuel, 2006. Atlantic hurricane trends linked to climate change. EOS, 87, 233-244.
Global mean surface temperature
Tropical Atlantic sea surface temperature
Sulfate aerosol radiative forcing
Best Fit Linear Combination of Global Warming Best Fit Linear Combination of Global Warming and Aerosol Forcing (red) versus Tropical Atlantic and Aerosol Forcing (red) versus Tropical Atlantic
SST (blue)SST (blue)
Mann, M. E., and K. A. Emanuel, 2006. Atlantic hurricane trends linked to climate change. EOS, 87, 233-244.
Tropical Atlantic sea surface temperature
Global Surface T + Aerosol Forcing
PhysicsPhysics
Energy Production: The HurricaneEnergy Production: The Hurricaneas a Carnot Heat Engineas a Carnot Heat Engine
0o 60oE 120oE 180oW 120oW 60oW
60oS
30oS
0o
30oN
60oN
0 10 20 30 40 50 60 70 80
Annual Maximum Potential Intensity (m/s)Annual Maximum Potential Intensity (m/s)
Observed Tropical Atlantic Potential IntensityObserved Tropical Atlantic Potential Intensity
Data Sources: NCAR/NCEP re-analysis with pre-1979 bias correction, UKMO/HADSST1
Emanuel, K., J. Climate, 2007
Effect of Increased Potential Effect of Increased Potential Intensity on Hurricane KatrinaIntensity on Hurricane Katrina
Projecting into the Future: Projecting into the Future: Downscaling from Global Downscaling from Global
Climate ModelsClimate Models
Today’s global climate Today’s global climate models are far too coarse to models are far too coarse to simulate tropical cyclonessimulate tropical cyclones
Our ApproachOur Approach• Step 1: Seed each ocean basin with a very large
number of weak, randomly located cyclones
• Step 2: Cyclones are assumed to move with the large scale atmospheric flow in which they are embedded
• Step 3: Run a coupled, ocean-atmosphere computer model for each cyclone, and note how many achieve at least tropical storm strength
• Step 4: Using the small fraction of surviving events, determine storm statistics.
200 Synthetic U.S. Landfalling tracks (color 200 Synthetic U.S. Landfalling tracks (color coded by Saffir-Simpson Scale)coded by Saffir-Simpson Scale)
CalibrationCalibration
• Absolute genesis frequency calibrated Absolute genesis frequency calibrated to North Atlantic during the period to North Atlantic during the period 1980-20051980-2005
Genesis ratesGenesis rates
AtlanticAtlantic
Eastern North Pacific
Western North Pacific
North Indian Ocean
Southern Hemisphere
Calibrated to AtlanticCalibrated to Atlantic
Seasonal CyclesSeasonal Cycles
AtlanticAtlantic
Cumulative Distribution of Storm Lifetime Cumulative Distribution of Storm Lifetime Peak Wind Speed, with Sample of 2946Peak Wind Speed, with Sample of 2946
Synthetic TracksSynthetic Tracks
Captures effects of regional climate Captures effects of regional climate phenomena (e.g. ENSO, AMM)phenomena (e.g. ENSO, AMM)
Global Percentage of Cat 4 & Cat 5 Global Percentage of Cat 4 & Cat 5 StormsStorms
Now Use Daily Output from IPCC Now Use Daily Output from IPCC Models to Derive Wind Models to Derive Wind
Statistics, Thermodynamic State Statistics, Thermodynamic State Needed by Synthetic Track Needed by Synthetic Track
TechniqueTechnique
1. Last 20 years of 20Last 20 years of 20thth century century simulationssimulations
2.2. Years 2180-2200 of IPCC Years 2180-2200 of IPCC Scenario A1b (COScenario A1b (CO22 stabilized at stabilized at
720 ppm)720 ppm)
Compare two simulations each Compare two simulations each from 7 IPCC models:from 7 IPCC models:
Basin-Wide Percentage Change Basin-Wide Percentage Change in Power Dissipationin Power Dissipation
7 Model Consensus Change in 7 Model Consensus Change in Storm FrequencyStorm Frequency
U.S. Coastal Damage PotentialU.S. Coastal Damage Potential
Summary:Summary:
• Tropical cyclones are sensitive to the Tropical cyclones are sensitive to the climate state, as revealed by historical climate state, as revealed by historical (and geological) data(and geological) data
• Observations together with detailed Observations together with detailed modeling suggest that TC power modeling suggest that TC power dissipation increases by ~65% for a dissipation increases by ~65% for a 10% increase in potential intensity10% increase in potential intensity
• New technique for downscaling climate New technique for downscaling climate models shows promise for predicting models shows promise for predicting response of global tropical cyclone response of global tropical cyclone activity to climate changeactivity to climate change
• Climate models may have systematic Climate models may have systematic errors that compromise estimates of errors that compromise estimates of tropical cyclone response to global tropical cyclone response to global warmingwarming
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