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Extreme Summer Temperatures Occur More Frequently

February 16, 2012

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Extreme summer temperatures are already occurring more frequently in the United States, and will become normal by mid-century if the world continues on a business as usual schedule of emitting greenhouse gases.

The white colored rock (approximately 100 feet high) shows the drop in the water level of Lake Mead as a result of the ongoing 10-year drought along the Colorado River.

Photo courtesy of Guy DeMeo , U.S. Geological Survey

By analyzing observations and results obtained from climate models, a study led by Phil Duffy of the Lawrence Livermore National Laboratory showed that previously rare high summertime (June, July and August) temperatures are already occurring more frequently in some regions of the 48 contiguous United States.

The Vegetation Drought Response Index (VegDRI) incorporates satellite observations of vegetation to monitor at a finer spatial detail than other commonly used drought indicators.

Photo courtesy of U.S. Geological Survey

“The observed increase in the frequency of previously rare summertime-average temperatures is more consistent with the consequences of increasing greenhouse gas concentrations than with the effects of natural climate variability,” said Duffy, who is the lead author of a report in a recent edition of the journal, Climatic Change. “It is extremely unlikely that the observed increase has happened through chance alone.”

The geographical patterns of increases in extreme summer temperatures that appear in observations are consistent with those that are seen in climate model simulations of the 20th century, Duffy said.

Duffy and colleague Claudia Tebaldi, a senior scientist at the nonprofit news and research group Climate Central, showed that the models project that previously rare summer temperatures will occur in well more than 50 percent of summers by mid-century throughout the lower 48 states.

The team first compared the period 1975-2000 to the preceding 25 years, and found that Full article here

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