Historical Summer Extremes to Become the Future Norm

Researchers from Boston University have estimated the effects near-term increases in global average temperatures will have on summertime temperatures across the globe, based on current warming trends and a desire to minimise overall warming to 2°C.

“We wanted to determine the impact such a temperature increase might have upon the frequency of seasonal-mean temperature extremes in various regions of the world, even if we were to avoid this target” said Bruce Anderson, associate professor of geography and environment and the study’s principal author.

“In particular, we wanted to determine if preventing the global-mean temperature increase from reaching this threshold would prevent extreme temperature values from becoming a normal occurrence in these regions.”

Anderson’s research showed that if a global temperature increase of 2°C came to pass, 70 to 80% of land surface will experience summer temperatures in at least half of all years that were usually only observed during historical extremes, which in this instance refere to the top 5% of summertime temperatures experienced during the second half of the 20th century.

“Many regions of the globe—including much of Africa, the southeastern and central portions of Asia, Indonesia, and the Amazon—are already committed to reaching this point, given current amounts of heat-trapping gases in the atmosphere” said Anderson.

On top of that, global-mean temperatures are expected to increase an additional 0.6°C (1°F) over the next few decades even if we managed to immediately halt the release of carbon dioxide, methane and other heat-trapping gases today.

The United States is expected to see the impacts of such warming primarily over the western third of the country.

“In these regions, if the 2°C threshold is passed, it is more likely than not that every summer will be an extreme summer compared with today,” Anderson explained. The region is expected to follow soon after Africa, Asia, and the Amazon as a region whose summertime temperatures will start echoing the extremes of the past 60 years. “While the western third of the U.S. is not committed to reaching such a situation, it is certainly on the brink.”

“While previous work, including our own and that of researchers at Stanford, has highlighted that summertime temperature extremes, and how frequently they occur, will change significantly even in response to relatively small increases in global-mean temperatures, the extent and immediacy of the results really caught us off guard,” said Anderson.

“Because these results are referenced to increases in global-mean temperatures, and not some particular time or change in amount of heat-trapping gases, they hold whether we reach this global-mean temperature increase in the next 40-50 years as currently projected, or the next century. They really are telling us that this is a temperature threshold that poses significant risks to our lives and livelihoods.”

Source: Springer
Image Source: Howard Brier

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