Hurricanes and Other Summer Storms

All storms, including thunderstorms, rain or snow storms, and tropical cyclones, are now developing in a warmer, moister environment. Consequently, storms are producing more heavy precipitation, even in areas where total precipitation is decreasing.1 General storminess around the world, as measured by wind speeds and ocean wave heights, has increased in recent years, with the increase particularly pronounced in winter months. This pattern cannot be explained by natural variability alone, and is consistent with  model simulations of a warming climate.2

Tropical Cyclones: Hurricanes, Typhoons, and Tropical Storms

Hurricane Intensity Increases with Rising Sea Surface Temperatures

Observed sea surface temperature (blue) and the Power Dissipation Index (green), which combines frequency, intensity and duration for North Atlantic hurricane rainfall and wind speeds are likely to increase in response to human caused warming. Analyses of model simulations suggest that for each 1.8°F increase in tropical sea surface temperatures, rainfall rates will increase by 6 to 18 percent.

Emanuel 2007

The intensity of Atlantic hurricanes has increased in recent years, a pattern that is consistent with climate change. Warming oceans store increasing amounts of heat energy and fuel stronger storms.3

Globally, the strongest tropical cyclones have increased in intensity, with the most significant increases occurring in the Atlantic. The available evidence is that this has been due to a combination of natural variability and climate change. Gaps in records from the last century and other issues make it difficult to be precise about the relative influences at this stage, but climate change is expected to dominate in the future.4

The Atlantic hurricane season is also getting longer, at a rate of 5 to 10 days per decade. The broadening of the season correlates with rising sea surface temperatures; each degree Celsius temperature change corresponds to a 20-day shift in both the beginning and end of hurricane season. Here too, however, due to the uneven state of record keeping, we cannot rule out the possibility of a role for natural variation in this trend.5

Atlantic Hurricane Intensity on the Rise

Looking forward, the trend is clearer. Over the coming decades, Atlantic hurricanes are likely to increase in strength as sea surface temperatures increase, fueling the intensity of storms in the Atlantic Ocean, and significantly increasing rainfall rates over those of present day storms.

Projected Changes in Atlantic Hurricane Frequency over the 21st Century

Adapted from NOAA Geophysical Fluid Dynamics Laboratory

Worldwide there will likely be an average increase in the maximum wind speed of tropical cyclones (hurricanes and typhoons) of 2 to 11%.6 Because of the way extremes respond to changes such as these, Category 4 and 5 hurricanes are expected to nearly double in number by the end of the century.7 The rate of rainfall associated with tropical cyclones, an important factor in flooding, is expected to increase approximately 20% within 100 km of the center of these storms.8

While the Atlantic basin is poised to see a dramatic increase in the number of very strong hurricanes, the global tropical cyclone count may decline slightly.9 The number of tropical cyclones is projected to decrease by 22% in the western North Pacific basin by the end of the 21st century.10

Thunderstorms and Tornadoes

Incomplete and inconsistent record keeping make it very difficult to assess how local thunderstorms and tornadoes in the United States have been affected by climate change to date. Looking forward, climate change creates a warmer, moister environment that may fuel additional thunderstorms. Computer models of a warming climate indicate that conditions may become more conducive to severe thunderstorms in some regions.11 Thunderstorms provide a favorable environment for tornado formation; but tornadoes also require wind shear, a highly uncertain element in climate models.

Extreme Winds

Average wind speed over a majority of the world’s oceans has increased 5 to 10% over the past 20 years, and the speed of extreme winds (the strongest 1% of winds) has increased by at least 15% over the majority of oceans.12 On the other hand, surface wind speed over land appears to be declining slightly in many mid-latitude locations, including the U.S.13 High-altitude circulation changes associated with climate change may affect wind speeds, but land use factors such as urban development and vegetation growth are also major contributors to slowing land surface winds.14

Next Page (Winter Storms) →

(Full List of References)

References

  1. Trenberth 2011
  2. Stott et al. 2010
  3. Trenberth 2011
  4. Knutson et al. 2010
  5. Kossin 2008
  6. Knutson et al. 2010
  7. Knutson et al. 2010 and Bender et al. 2010
  8. Knutson et al. 2010
  9. Knutson et al. 2010
  10. Murakami et al. 2011
  11. Gutowski et al. 2008 and Trapp et al. 2007
  12. Young et al. 2011
  13. Vautard et al 2010, McVicar & Roderick 2010, Pryor et al 2009
  14. Vautard et al 2010