Climatologists Predict More Extreme Summer Temperatures in 21st Century
February 16, 2012

Climatologists Predict More Extreme Summer Temperatures in 21st Century

A new report published by an American non-profit research center says that extreme summer temperatures are becoming increasingly commonplace in the United States, a trend that they project will continue throughout the 21st century.

Climatologist Phil Duffy led a group of researchers at the Lawrence Livermore National Laboratory (LLNL) in California in analyzing the results of various climate models examining the occurrence of extreme high temperatures in the summer months of June, July and August. They found that higher than average spikes in temperature are becoming increasingly common in various regions of the lower 48 states.

“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,” Duffy wrote in the report published this week in the journal Climatic Change.

“It is extremely unlikely that the observed increase has happened through chance alone,” he added, highlighting what his team believes to be the anthropogenic cause behind the soaring temperatures.

Together with his colleague Claudia Tebaldi from the research group Climate Central, Duffy´s computer models indicated that sweltering summer temperatures — once something of a rarity — can be expected in at least half of our summers before the middle of this century.

The researchers started out by comparing the quarter century between 1975 and 2000 with the preceding  25 years. They say that the recorded data corresponded with the predictions of some 16 global climate models, all of which indicated that high temperatures that were seldom in the earlier period occurred with greater frequency in the latter period in some regions.

Duffy´s team claims the very similar results acquired from observations and computer models indicate that the models are, in fact, able to accurately simulate and predict changes in climate patterns. They also referred to statistical analyses to argue that the rising temperatures are most likely not a result of random variations in weather patterns.

Moving forward, the team then used current data from a climate model for the period from 1995 — 2024 and found that the trend towards the increasing frequency of high temperatures persisted.

For their last analyses, Duffy and Tebaldi looked at the results from models for the period from 2035 to 2064 and found that extreme summertime temperatures became the norm, occurring in a majority of years in high summer. The high temperatures that were only found in about 5 percent of the summers during the 1950-1979 period were predicted to occur at least 70 percent of the time by the middle of this century.

“The South, Southwest and Northeast are projected to experience the largest increases in the frequency of unusually hot summers,” Duffy said.

“The strong increase in extremes in the Southwest and Northeast are explained by strong historical and projected warming there,” he added.

“What was historically a one in 20-year occurrence will occur with at least a 70 percent chance every year. This work shows an example of how climate change can affect weather extremes, as well as averages.”


Image Caption: 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


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