Scientific Assessment of Effects of Changing Climate on Extreme Weather Events in North America

June 19, 2008 

Source National Oceanic and Atmostpheric Administration,

United States Department of Commerce 

The U.S. Climate Change Science Program and the Subcommittee on Global Change Research today released a scientific assessment that provides the first comprehensive analysis of observed and projected changes in weather and climate extremes in North America and U.S. territories. The Intergovernmental Panel on Climate Change previously evaluated extreme weather and climate events on a global basis in this same context. However, there has not been a specific assessment across North America prior to this report.

Among the major findings reported in this assessment are that droughts, heavy downpours, excessive heat, and intense hurricanes are likely to become more commonplace as humans continue to increase the atmospheric concentrations of heat-trapping greenhouse gases.

The report is based on scientific evidence that a warming world will be accompanied by changes in the intensity, duration, frequency, and geographic extent of weather and climate extremes.

"This report addresses one of the most frequently asked questions about global warming: what will happen to weather and climate extremes? This synthesis and assessment product examines this question across North America and concludes that we are now witnessing and will increasingly experience more extreme weather and climate events.

"We will continue to see some of the biggest impacts of global warming coming from changes in weather and climate extremes,” said report co-chair Gerry Meehl, Ph.D., of the National Center for Atmospheric Research in Boulder, Colo. "This report focuses for the first time on changes of extremes specifically over North America."

The full CCSP 3.3 report, Weather and Climate Extremes in a Changing Climate, and a summary FAQ brochure are available online.

Global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases, according to the report. Many types of extreme weather and climate event changes have been observed during this time period and continued changes are projected for this century. Specific future projections include:

• Abnormally hot days and nights, along with heat waves, are very likely to become more common. Cold nights are very likely to become less common.
• Sea ice extent is expected to continue to decrease and may even disappear in the Arctic Ocean in summer in coming decades.
• Precipitation, on average, is likely to be less frequent but more intense.
• Droughts are likely to become more frequent and severe in some regions.
• Hurricanes will likely have increased precipitation and wind.
• The strongest cold-season storms in the Atlantic and Pacific are likely to produce stronger winds and higher extreme wave heights.

NOAA plays a key role in the Climate Change Science Program, which is responsible for coordinating and integrating climate research, observations, decision support, and communications of 13 federal departments and agencies.

The National Center for Atmospheric Research investigates climate, weather, and other topics related to the atmosphere. It is sponsored by the National Science Foundation and managed by a nonprofit consortium of universities, the University Corporation for Atmospheric Research.

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