Study sees permanent hotter summers

PALO ALTO, Calif., June 6 (UPI) -- Many regions of the world will see hotter summers in the next 20 to 60 years if greenhouse gas concentrations keep rising, U.S. researchers say.

Climate scientists at Stanford University predict many tropical regions in Africa, Asia and South America could see "the permanent emergence of unprecedented summer heat" in the next two decades, while the middle latitudes of Europe, China and North America, including the United States, are likely to undergo extreme summer temperature shifts within 60 years, a Stanford release reported Monday.

"According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years," study author Noah Diffenbaugh, an assistant professor of environmental science, said.

"When scientists talk about global warming causing more heat waves, people often ask if that means that the hottest temperatures will become 'the new normal,'" Diffenbaugh said. "That got us thinking -- at what point can we expect the coolest seasonal temperatures to always be hotter than the historically highest temperatures for that season?"

An analysis of more than 50 climate model experiments revealed that many parts of the planet could experience a permanent spike in seasonal temperatures within 60 years, the researchers said.

Climate models suggest the tropics are heating up the fastest, they said.

"We find that the most immediate increase in extreme seasonal heat occurs in the tropics, with up to 70 percent of seasons in the early 21st century (2010-2039) exceeding the late-20th century maximum," the researchers said.