This website is the digital version of the 2014 National Climate Assessment, produced in collaboration with the U.S. Global Change Research Program.

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Welcome to the National Climate Assessment

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

Explore the effects of climate change
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Changes in Hurricanes

The intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest hurricanes, have all increased since the early 1980s. Hurricane intensity and rainfall are projected to increase as the climate continues to warm.

Explore changes in hurricanes.

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Convening Lead Authors

John Walsh, University of Alaska Fairbanks

Donald Wuebbles, University of Illinois

Lead Authors

Katharine Hayhoe, Texas Tech University

James Kossin, NOAA, National Climatic Data Center

Kenneth Kunkel, CICS-NC, North Carolina State Univ., NOAA National Climatic Data Center

Graeme Stephens, NASA Jet Propulsion Laboratory

Peter Thorne, Nansen Environmental and Remote Sensing Center

Russell Vose, NOAA National Climatic Data Center

Michael Wehner, Lawrence Berkeley National Laboratory

Josh Willis, NASA Jet Propulsion Laboratory

Contributing Authors

David Anderson, NOAA, National Climatic Data Center

Scott Doney, Woods Hole Oceanographic Institution

Richard Feely, NOAA Pacific Marine Environmental Laboratory

Paula Hennon, CICS-NC, North Carolina State Univ., NOAA National Climatic Data Center

Viatcheslav Kharin, Canadian Centre for Climate Modelling and Analysis, Environment Canada

Thomas Knutson, NOAA Geophysical Fluid Dynamics Laboratory

Felix Landerer, NASA Jet Propulsion Laboratory

Tim Lenton, Exeter University

John Kennedy, UK Meteorological Office

Richard Somerville, Scripps Institution of Oceanography, Univ. of California, San Diego

Introduction

This chapter summarizes how climate is changing, why it is changing, and what is projected for the future. While the focus is on changes in the United States, the need to provide context sometimes requires a broader geographical perspective. Additional geographic detail is presented in the regional chapters of this report. Further details on the topics covered by this chapter are provided in the Climate Science Supplement and Frequently Asked Questions Appendices.

The chapter presents 12 key messages about our changing climate, together with supporting evidence for those messages. The discussion of each key message begins with a summary of recent variations or trends, followed by projections of the corresponding changes for the future.

Key Message 8: Changes in Hurricanes

The intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have all increased since the early 1980s. The relative contributions of human and natural causes to these increases are still uncertain. Hurricane-associated storm intensity and rainfall rates are projected to increase as the climate continues to warm.

Supporting Evidence
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Supporting Evidence

Process for Developing Key Messages

Development of the key messages involved discussions of the lead authors and accompanying analyses conducted via one in-person meeting plus multiple teleconferences and email exchanges from February thru September 2012. The authors reviewed 80 technical inputs provided by the public, as well as other published literature, and applied their professional judgment.

Key message development also involved the findings from four special workshops that related to the latest scientific understanding of climate extremes. Each workshop had a different theme related to climate extremes, had approximately 30 attendees (the CMIP5 meeting had more than 100), and the workshops resulted in a paper.7 The first workshop was held in July 2011, titled Monitoring Changes in Extreme Storm Statistics: State of Knowledge.8 The second was held in November 2011, titled Forum on Trends and Causes of Observed Changes in Heatwaves, Coldwaves, Floods, and Drought.9 The third was held in January 2012, titled Forum on Trends in Extreme Winds, Waves, and Extratropical Storms along the Coasts.10 The fourth, the CMIP5 results workshop, was held in March 2012 in Hawai‘i, and resulted in an analysis of CMIP5 results relative to climate extremes in the United States.7

The Chapter Author Team’s discussions were supported by targeted consultation with additional experts. Professional expertise and judgment led to determining “key vulnerabilities.” A consensus-based approach was used for final key message selection.

Description of evidence base

The key message and supporting text summarize extensive evidence documented in the climate science peer-reviewed literature. Technical Input reports (82) on a wide range of topics were also reviewed; they were received as part of the Federal Register Notice solicitation for public input.

Recent studies suggest that the most intense Atlantic hurricanes have become stronger since the early 1980s.1 While this is still the subject of active research, this trend is projected to continue.2,3

New information and remaining uncertainties

Detecting trends in Atlantic and eastern North Pacific hurricane activity is challenged by a lack of consistent historical data and limited understanding of all of the complex interactions between the atmosphere and ocean that influence hurricanes.4,5,6

While the best analyses to date4,3suggest an increase in intensity and in the number of the most intense hurricanes over this century, there remain significant uncertainties.

Assessment of confidence based on evidence

Given the evidence base and remaining uncertainties:

High confidence that the intensity, frequency, and duration of North Atlantic hurricanes, as well as the frequency of the strongest (Category 4 and 5) hurricanes, have increased substantially since the early 1980s.

Low confidence in relative contributions of human and natural causes in the increases.

Medium confidence that hurricane intensity and rainfall rates are projected to increase as the climate continues to warm.

Confidence Level

Very High

Strong evidence (established theory, multiple sources, consistent results, well documented and accepted methods, etc.), high consensus

High

Moderate evidence (several sources, some consistency, methods vary and/or documentation limited, etc.), medium consensus

Medium

Suggestive evidence (a few sources, limited consistency, models incomplete, methods emerging, etc.), competing schools of thought

Low

Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.), disagreement or lack of opinions among experts

Changes in Hurricanes

There has been a substantial increase in most measures of Atlantic hurricane activity since the early 1980s, the period during which high-quality satellite data are available.13,14,15,16,17 These include measures of intensity, frequency, and duration as well as the number of strongest (Category 4 and 5) storms. The ability to assess longer-term trends in hurricane activity is limited by the quality of available data. The historic record of Atlantic hurricanes dates back to the mid-1800s, and indicates other decades of high activity. However, there is considerable uncertainty in the record prior to the satellite era (early 1970s), and the further back in time one goes, the more uncertain the record becomes.14,15

Figure 2.23: Observed Trends in Hurricane Power Dissipation Observed Trends in Hurricane Power Dissipation Details/Download

The recent increases in activity are linked, in part, to higher sea surface temperatures in the region that Atlantic hurricanes form in and move through. Numerous factors have been shown to influence these local sea surface temperatures, including natural variability, human-induced emissions of heat-trapping gases, and particulate pollution. Quantifying the relative contributions of natural and human-caused factors is an active focus of research. Some studies suggest that natural variability, which includes the Atlantic Multidecadal Oscillation, is the dominant cause of the warming trend in the Atlantic since the 1970s,18,19,20 while others argue that human-caused heat-trapping gases and particulate pollution are more important.21,22

Hurricane development, however, is influenced by more than just sea surface temperature. How hurricanes develop also depends on how the local atmosphere responds to changes in local sea surface temperatures, and this atmospheric response depends critically on the cause of the change.23,24 For example, the atmosphere responds differently when local sea surface temperatures increase due to a local decrease of particulate pollution that allows more sunlight through to warm the ocean, versus when sea surface temperatures increase more uniformly around the world due to increased amounts of human-caused heat-trapping gases.18,25,26,27 So the link between hurricanes and ocean temperatures is complex. Improving our understanding of the relationships between warming tropical oceans and tropical cyclones is another active area of research.

Changes in the average length and positions of Atlantic storm tracks are also associated with regional climate variability.28 The locations and frequency of storms striking land have been argued to vary in opposing ways than basin-wide frequency. For example, fewer storms have been observed to strike land during warmer years even though overall activity is higher than average,29 which may help to explain the lack of any clear trend in landfall frequency along the U.S. eastern and Gulf coasts.4,5,6 Climate models also project changes in hurricane tracks and where they strike land.30 The specific characteristics of the changes are being actively studied.

Other measures of Atlantic storm activity are projected to change as well.4,2,3 By late this century, models, on average, project a slight decrease in the annual number of tropical cyclones, but an increase in the number of the strongest (Category 4 and 5) hurricanes. These projected changes are based on an average of projections from a number of individual models, and they represent the most likely outcome. There is some uncertainty in this as the individual models do not always agree on the amount of projected change, and some models may project an increase where others project a decrease. The models are in better agreement when projecting changes in hurricane precipitation – almost all existing studies project greater rainfall rates in hurricanes in a warmer climate, with projected increases of about 20% averaged near the center of hurricanes.

References

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  2. Bender, M. A., T. R. Knutson, R. E. Tuleya, J. J. Sirutis, G. A. Vecchi, S. T. Garner, and I. M. Held, 2010: Modeled impact of anthropogenic warming on the frequency of intense Atlantic hurricanes. Science, 327, 454-458, doi:10.1126/science.1180568.

  3. Booth, B. B. B., N. J. Dunstone, P. R. Halloran, T. Andrews, and N. Bellouin, 2012: Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability. Nature, 484, 228-232, doi:10.1038/nature10946.

  4. Camargo, S. J., M. Ting, and Y. Kushnir, 2013: Influence of local and remote SST on North Atlantic tropical cyclone potential intensity. Climate Dynamics, 40, 1515-1529, doi:10.1007/s00382-012-1536-4.

  5. Emanuel, K., 2007: Environmental factors affecting tropical cyclone power dissipation. Journal of Climate, 20, 5497-5509, doi:10.1175/2007JCLI1571.1.

  6. Emanuel, K., and A. Sobel, 2013: Response of tropical sea surface temperature, precipitation, and tropical cyclone-related variables to changes in global and local forcing. Journal of Advances in Modeling Earth Systems, 5, 447-458, doi:10.1002/jame.20032. URL

  7. Knapp, K. R., M. C. Kruk, D. H. Levinson, H. J. Diamond, and C. J. Neumann, 2010: The International Best Track Archive for Climate Stewardship (IBTrACS). Bulletin of the American Meteorological Society, 91, 363-376, doi:10.1175/2009BAMS2755.1. URL

  8. Knutson, T. R., J. L. McBride, J. Chan, K. Emanuel, G. Holland, C. Landsea, I. Held, J. P. Kossin, A. K. Srivastava, and M. Sugi, 2010: Tropical cyclones and climate change. Nature Geoscience, 3, 157-163, doi:10.1038/ngeo779.

  9. Knutson, T. R., J. J. Sirutis, G. A. Vecchi, S. Garner, M. Zhao, H. - S. Kim, M. Bender, R. E. Tuleya, I. M. Held, and G. Villarini, 2013: Dynamical downscaling projections of twenty-first-century Atlantic hurricane activity: CMIP3 and CMIP5 model-based scenarios. Journal of Climate, 27, 6591-6617, doi:10.1175/jcli-d-12-00539.1. URL

  10. Kossin, J. P., K. R. Knapp, D. J. Vimont, R. J. Murnane, and B. A. Harper, 2007: A globally consistent reanalysis of hurricane variability and trends. Geophysical Research Letters, 34, L04815, doi:10.1029/2006GL028836. URL

  11. Kossin, J. P., S. J. Camargo, and M. Sitkowski, 2010: Climate modulation of North Atlantic hurricane tracks. Journal of Climate, 23, 3057-3076, doi:10.1175/2010jcli3497.1. URL

  12. Kossin, J. P., T. L. Olander, and K. R. Knapp, 2013: Trend analysis with a new global record of tropical cyclone intensity. Journal of Climate, 26, 9960-9976, doi:10.1175/JCLI-D-13-00262.1.

  13. Kunkel, K. E. et al., 2013: Monitoring and understanding trends in extreme storms: State of knowledge. Bulletin of the American Meteorological Society, 94, doi:10.1175/BAMS-D-11-00262.1. URL

  14. Landsea, C. W., and J. L. Franklin, 2013: Atlantic hurricane database uncertainty and presentation of a new database format. Monthly Weather Review, 141, 3576-3592, doi:10.1175/MWR-D-12-00254.1. URL

  15. Mann, M. E., and K. A. Emanuel, 2006: Atlantic hurricane trends linked to climate change. Eos, Transactions, American Geophysical Union, 87, 233-244, doi:10.1029/2006EO240001. URL

  16. Murakami, H., and B. Wang, 2010: Future change of North Atlantic tropical cyclone tracks: Projection by a 20-km-mesh global atmospheric model. Journal of Climate, 23, 2699-2721, doi:10.1175/2010jcli3338.1. URL

  17. Peterson, T. C. et al., 2013: Monitoring and understanding changes in heat waves, cold waves, floods and droughts in the United States: State of knowledge. Bulletin of the American Meteorological Society, 94, 821-834, doi:10.1175/BAMS-D-12-00066.1. URL

  18. Ramsay, H. A., and A. H. Sobel, 2011: Effects of relative and absolute sea surface temperature on tropical cyclone potential intensity using a single-column model. Journal of Climate, 24, 183-193, doi:10.1175/2010jcli3690.1. URL

  19. Seneviratne, S. I., N. Nicholls, D. Easterling, C. M. Goodess, S. Kanae, J. Kossin, Y. Luo, J. Marengo, K. McInnes, M. Rahimi, M. Reichstein, A. Sorteberg, C. Vera, and X. Zhang, 2012: Ch. 3: Changes in climate extremes and their impacts on the natural physical environment. Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC), C.B. Field, V. Barros, T.F. Stocker, Q. Dahe, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley, Eds., Cambridge University Press, 109-230.

  20. Ting, M., Y. Kushnir, R. Seager, and C. Li, 2009: Forced and internal twentieth-century SST Trends in the North Atlantic. Journal of Climate, 22, 1469-1481, doi:10.1175/2008JCLI2561.1.

  21. Torn, R. D., and C. Snyder, 2012: Uncertainty of tropical cyclone best-track information. Weather and Forecasting, 27, 715-729, doi:10.1175/waf-d-11-00085.1. URL

  22. Vecchi, G. A., and B. J. Soden, 2007: Effect of remote sea surface temperature change on tropical cyclone potential intensity. Nature, 450, 1066-1070, doi:10.1038/nature06423.

  23. Vecchi, G. A., A. Clement, and B. J. Soden, 2008: Examining the tropical Pacific's response to global warming. Eos, Transactions, American Geophysical Union, 89, 81-83, doi:10.1029/2008EO090002.

  24. Villarini, G., G. A. Vecchi, and J. A. Smith, 2012: U.S. landfalling and North Atlantic hurricanes: Statistical modeling of their frequencies and ratios. Monthly Weather Review, 140, 44-65, doi:10.1175/mwr-d-11-00063.1. URL

  25. Vose, R. S. et al., 2013: Monitoring and understanding changes in extremes: Extratropical storms, winds, and waves. Bulletin of the American Meteorological Society, in press, doi:10.1175/BAMS-D-12-00162.1. URL

  26. Wang, C., H. Liu, S. - K. Lee, and R. Atlas, 2011: Impact of the Atlantic warm pool on United States landfalling hurricanes. Geophysical Research Letters, 38, L19702, doi:10.1029/2011gl049265. URL

  27. Weinkle, J., R. Maue, and R. Pielke, Jr., 2012: Historical global tropical cyclone landfalls. Journal of Climate, 25, 4729-4735, doi:10.1175/jcli-d-11-00719.1. URL

  28. Wuebbles, D. J., G. Meehl, K. Hayhoe, T. R. Karl, K. Kunkel, B. Santer, M. Wehner, B. Colle, E. M. Fischer, R. Fu, A. Goodman, E. Janssen, H. Lee, W. Li, L. N. Long, S. Olsen, A. J. Sheffield, and L. Sun, 2013: CMIP5 climate model analyses: Climate extremes in the United States. Bulletin of the American Meteorological Society, in press, doi:10.1175/BAMS-D-12-00172.1. URL

  29. Zhang, R., and T. L. Delworth, 2009: A new method for attributing climate variations over the Atlantic Hurricane Basin's main development region. Geophysical Research Letters, 36, 5, doi:10.1029/2009GL037260.

  30. Zhang, R., T. L. Delworth, R. Sutton, D. L. R. Hodson, K. W. Dixon, I. M. Held, Y. Kushnir, J. Marshall, Y. Ming, R. Msadek, J. Robson, A. J. Rosati, M. F. Ting, and G. A. Vecchi, 2013: Have aerosols caused the observed Atlantic multidecadal variability? Journal of the Atmospheric Sciences, 70, 1135-1144, doi:10.1175/jas-d-12-0331.1.

The National Climate Assessment summarizes the impacts of climate change on the United States, now and in the future.

A team of more than 300 experts guided by a 60-member Federal Advisory Committee produced the report, which was extensively reviewed by the public and experts, including federal agencies and a panel of the National Academy of Sciences.

United States Global Change Research Program logo United States Global Change Research Program participating agency logos