Is Global Warming Affecting Hurricanes

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Program. Overview of hurricane risk Evidence connecting hurricane activity to tropical sea surface temperatureThe evidence for anthropogenic forcing of tropical ocean temperatureThe future. Hurricane Risk. Tropical cyclones account for the bulk of natural catastrophe U.S. insurance losses Losses vary roughly as the cube of the maximum wind speedKatrina caused > 1300 deaths and > $130 billion in damage.
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Is Global Warming Affecting Hurricanes

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1. Is Global Warming Affecting Hurricanes? Kerry Emanuel Massachusetts Institute of Technology Are hurricanes becoming more powerful and destructive? Are these changes due to a natural cycle of hurricane activity or are they caused by human-induced climate change? Although this is currently a hot debate among scientists, new research suggests that the destructive potential of hurricanes is increasing due to the heating of the oceans. Image: Satellite image of Hurricane Floyd approaching the east coast of Florida in 1999. The image has been digitally enhanced to lend a three-dimensional perspective. Credit: NASA/Goddard Space Flight Center. Are hurricanes becoming more powerful and destructive? Are these changes due to a natural cycle of hurricane activity or are they caused by human-induced climate change? Although this is currently a hot debate among scientists, new research suggests that the destructive potential of hurricanes is increasing due to the heating of the oceans. Image: Satellite image of Hurricane Floyd approaching the east coast of Florida in 1999. The image has been digitally enhanced to lend a three-dimensional perspective. Credit: NASA/Goddard Space Flight Center.

2. Program Overview of hurricane risk Evidence connecting hurricane activity to tropical sea surface temperature The evidence for anthropogenic forcing of tropical ocean temperature The future

3. Hurricane Risk Tropical cyclones account for the bulk of natural catastrophe U.S. insurance losses Losses vary roughly as the cube of the maximum wind speed Katrina caused > 1300 deaths and > $130 billion in damage

9. Summary of U.S. Hurricane Damage Statistics: >50% of all normalized damage caused by top 8 events, all category 3, 4 and 5 >90% of all damage caused by storms of category 3 and greater Category 3,4 and 5 events are only 13% of total landfalling events; only 30 since 1870 Landfalling storm statistics are grossly inadequate for assessing hurricane risk

10. Part II: Evidence Connecting Hurricane Activity to Tropical Sea Surface Temperature

11. No Long-Term Trend in Global Frequency This graph documents the annual number of tropical cyclones globally since 1970, the first year that meteorologists deem to have a complete satellite network. Before 1970, ?some storms that never made landfall or affected a ship were probably missed. This graph documents the annual number of tropical cyclones globally since 1970, the first year that meteorologists deem to have a complete satellite network. Before 1970, ?some storms that never made landfall or affected a ship were probably missed.

12. Intensity Metric: The Power Dissipation Index

13. Power Dissipation Based on 3 Data Sets for the Western North Pacific (smoothed with a 1-3-4-3-1 filter)

14. This graph adds ocean surface temperature to the previous graph for comparison.This graph adds ocean surface temperature to the previous graph for comparison.

15. This graph is similar to the previous graph, ?but the ocean surface temperature has been added for comparison. The low value of storm power in the early 1940s is thought to be due to the lack of reports from ships at sea because of the radio silence imposed during WWII. This graph is similar to the previous graph, ?but the ocean surface temperature has been added for comparison. The low value of storm power in the early 1940s is thought to be due to the lack of reports from ships at sea because of the radio silence imposed during WWII.

17. What Environmental Factors Control Hurricane Power Dissipation? Potential Intensity Wind Shear Low level environmental vorticity (?spin?)

20. Maximum Theoretical Wind Speed, Vpot

21. Potential intensity and SST can be changed by: Changing solar and infrared radiation Changing ocean mixed layer entrainment Changing mean surface wind speed

25. Contributions to North Atlantic Hurricane Power Dissipation:

26.

27. What you are looking at is the tropical North Atlantic ocean temperature (in blue), as before but smoothed over 10 years, compared to the average surface temperature of the whole Northern Hemisphere, including land (in green), both for the months August-October. Late summer ? early fall tropical North Atlantic sea surface temperature is highly correlated with Northern Hemisphere surface temperature (including land).What you are looking at is the tropical North Atlantic ocean temperature (in blue), as before but smoothed over 10 years, compared to the average surface temperature of the whole Northern Hemisphere, including land (in green), both for the months August-October. Late summer ? early fall tropical North Atlantic sea surface temperature is highly correlated with Northern Hemisphere surface temperature (including land).

28. What is Controlling Northern Hemisphere Surface Temperature?

29. Slides 41-46 are from the upcoming IPCC report, due out on February, 2007. THESE MUST NOT BE PUBLISHED IN ANY FORM PRIOR TO THAT TIME. They were not included on the CD-ROM and will be blocked from the webcast. Slides 41-46 are from the upcoming IPCC report, due out on February, 2007. THESE MUST NOT BE PUBLISHED IN ANY FORM PRIOR TO THAT TIME. They were not included on the CD-ROM and will be blocked from the webcast.

30. Greenhouse Gases and Associated Radiative Forcing have been Increasing Slides 41-46 are from the upcoming IPCC report, due out on February, 2007. THESE MUST NOT BE PUBLISHED IN ANY FORM PRIOR TO THAT TIME. They were not included on the CD-ROM and will be blocked from the webcast. Slides 41-46 are from the upcoming IPCC report, due out on February, 2007. THESE MUST NOT BE PUBLISHED IN ANY FORM PRIOR TO THAT TIME. They were not included on the CD-ROM and will be blocked from the webcast.

31. Slides 41-46 are from the upcoming IPCC report, due out on February, 2007. THESE MUST NOT BE PUBLISHED IN ANY FORM PRIOR TO THAT TIME. They were not included on the CD-ROM and will be blocked from the webcast. Slides 41-46 are from the upcoming IPCC report, due out on February, 2007. THESE MUST NOT BE PUBLISHED IN ANY FORM PRIOR TO THAT TIME. They were not included on the CD-ROM and will be blocked from the webcast.

33. Northern hemisphere surface temperature (and late summer-early fall tropical Atlantic sea surface temperature) represents a linear combination of global warming and aerosol cooling Mann and Emanuel?s Hypothesis about Why the Northern Hemisphere Differs from the Globe (2006): Northern hemisphere surface temperature (and late summer-early fall tropical Atlantic sea surface temperature) represents a linear combination of global warming and aerosol cooling.Mann and Emanuel?s Hypothesis about Why the Northern Hemisphere Differs from the Globe (2006): Northern hemisphere surface temperature (and late summer-early fall tropical Atlantic sea surface temperature) represents a linear combination of global warming and aerosol cooling.

34. Tropical Atlantic SST(blue), Global Mean Surface Temperature (red), Aerosol Forcing (aqua) Analyses of sea surface temperature (SST) series that have been decadally smoothed August-September-October (ASO) main development region (MDR) sea surface temperature (SST) series T(t) and estimated components for both (1) univariate regression and (2) bivariate regression (for more information see ftp://texmex.mit.edu/pub/emanuel/PAPERS/EOS_mann_emanuel_2006.pdf). Definitions Univariate statistics includes all statistical techniques for analyzing a single variable of interest. Bivariate regression is a procedure of deriving a mathematical relationship, in the form of an equation, between a single metric dependent variable and a single metric independent variable. Sources: Applied Multivariate Statistical Analysis (www.stat.psu.edu/~rathbun/stat505/slides/Intro.pdf#search=%22define%20univariate%20%22). Malhotra, N. K., 2006: Marketing Research: An Applied Orientation, Fifth Edition. Prentice Hall, 864 pp. Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244. Image: Tropical Atlantic SST(blue), Global Mean Surface Temperature (red), Aerosol Forcing (aqua). Credit: Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244. Analyses of sea surface temperature (SST) series that have been decadally smoothed August-September-October (ASO) main development region (MDR) sea surface temperature (SST) series T(t) and estimated components for both (1) univariate regression and (2) bivariate regression (for more information see ftp://texmex.mit.edu/pub/emanuel/PAPERS/EOS_mann_emanuel_2006.pdf). Definitions Univariate statistics includes all statistical techniques for analyzing a single variable of interest. Bivariate regression is a procedure of deriving a mathematical relationship, in the form of an equation, between a single metric dependent variable and a single metric independent variable. Sources: Applied Multivariate Statistical Analysis (www.stat.psu.edu/~rathbun/stat505/slides/Intro.pdf#search=%22define%20univariate%20%22). Malhotra, N. K., 2006: Marketing Research: An Applied Orientation, Fifth Edition. Prentice Hall, 864 pp. Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244. Image: Tropical Atlantic SST(blue), Global Mean Surface Temperature (red), Aerosol Forcing (aqua). Credit: Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244.

35. Best Fit Linear Combination of Global Warming and Aerosol Forcing (red) versus Tropical Atlantic SST (blue) This graph show the results of a bivariate statistical model based on the sum of both regression components shown in the previous slide. Shown also is the fit of the regression model based on the restricted interval 1870?1969 and the prediction of T(t) over the subsequent 30 years (1970?1999) based on that regression model (for more information see ftp://texmex.mit.edu/pub/emanuel/PAPERS/EOS_mann_emanuel_2006.pdf). Source: Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244. Image: Best Fit Linear Combination of Global Warming and Aerosol Forcing (red) versus Tropical Atlantic SST (blue). Credit: Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244. This graph show the results of a bivariate statistical model based on the sum of both regression components shown in the previous slide. Shown also is the fit of the regression model based on the restricted interval 1870?1969 and the prediction of T(t) over the subsequent 30 years (1970?1999) based on that regression model (for more information see ftp://texmex.mit.edu/pub/emanuel/PAPERS/EOS_mann_emanuel_2006.pdf). Source: Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244. Image: Best Fit Linear Combination of Global Warming and Aerosol Forcing (red) versus Tropical Atlantic SST (blue). Credit: Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. EOS, 87, 233-244.

36.

37. Projections of Tropical Cyclone Activity: Downscaling from Global Climate Models

38. Using Physics to Improve Hurricane Risk Assessment Generate very large number of synthetic storm tracks consistent with the general circulation of the atmosphere in a given climate Run a coupled ocean-atmosphere model of hurricane intensity along each track to generate wind fields

40. Cumulative Distribution of Storm Lifetime Peak Wind Speed, with Sample of 2946 Synthetic Tracks

41. Use Daily Output from Climate Models to Derive Wind Statistics, Thermodynamic State Needed by Synthetic Track Technique (but hold genesis PDF constant!)

42. Compare two simulations from IPCC set: 1. Last 20 years of 20th century simulations 2. Years 2180-2200 of IPCC Scenario A1b (CO2 stabilized at 720 ppm)

45. Summary Atlantic TC frequency, intensity and duration are co-varying with tropical Atlantic SST Changes in tropical cyclone power are driven by changing potential intensity, wind shear, and ?spin? of the low-level winds

46. Changes in tropical North Atlantic sea temperature mirror changes in northern hemispheric temperature and are probably driven by a combination of cooling by volcanoes and air pollution, and warming by greenhouse gases Long-term risk assessments must account for climate change

47. Scientific Basis of the ?Natural Cycles? Story

48. Power Spectrum of North Atlantic Hurricane Frequency, 1851-2005

49. The Atlantic Multi-decadal Oscillation (AMO) is thought to be a natural cycle of the Atlantic climate, affecting sea surface temperature, winds, and other quantities, including hurricanes. This graphs shows the difference in ocean temperature between the top of the cycle and the bottom. Image: The AMO and Sea Surface Temperatures. Credit: Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nu?ez, and W. M. Gray., 2001. The recent increase in Atlantic hurricane activity: causes and implications. Science, 293, 474-479. The Atlantic Multi-decadal Oscillation (AMO) is thought to be a natural cycle of the Atlantic climate, affecting sea surface temperature, winds, and other quantities, including hurricanes. This graphs shows the difference in ocean temperature between the top of the cycle and the bottom. Image: The AMO and Sea Surface Temperatures. Credit: Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nu?ez, and W. M. Gray., 2001. The recent increase in Atlantic hurricane activity: causes and implications. Science, 293, 474-479.

52. We can derive the ?AMO? signal merely be ?de-trending? the NH mean surface temperature We can derive the ?AMO? signal merely be ?de-trending? the NH mean surface temperature

53. The ?AMO? signal can be derived by merely ?de-trending? the Northern Hemisphere mean surface temperature. Top image: De-trended Aug-Oct Northern Hemisphere Surface Temperature. Source: Hadley Centre Global Surface Temperature Data. Bottom image: Variation with Time of the Strength of the AMO. Credit: Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nu?ez, and W. M. Gray., 2001. The recent increase in Atlantic hurricane activity: causes and implications. Science, 293, 474-479. The ?AMO? signal can be derived by merely ?de-trending? the Northern Hemisphere mean surface temperature. Top image: De-trended Aug-Oct Northern Hemisphere Surface Temperature. Source: Hadley Centre Global Surface Temperature Data. Bottom image: Variation with Time of the Strength of the AMO. Credit: Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nu?ez, and W. M. Gray., 2001. The recent increase in Atlantic hurricane activity: causes and implications. Science, 293, 474-479.

54. 3000 Atlantic storms in the current climate

55. Boston


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