Eastern U.S. summers to be hotter, NASA finds

updated 10:12 p.m. ET May 10, 2007

WASHINGTON - Future Eastern United States summers look much hotter than originally predicted, with daily highs about 10 degrees warmer than in recent years by the mid-2080s, a new NASA study says.

Previous and widely used global warming computer estimates predict too many rainy days, the study says. Because drier weather is hotter, they underestimate how warm it will be east of the Mississippi River, said atmospheric scientists Barry Lynn and Leonard Druyan of Columbia University and NASA's Goddard Institute for Space Studies.

"Unless we take some strong action to curtail carbon dioxide emissions, it's going to get a lot hotter," said Lynn, now a scientist at Hebrew University of Jerusalem. "It's going to be a lot more dangerous for people who are not in the best of health."

The study got mixed reviews from other climate scientists, in part because the Eastern United States has recently been wetter and cooler than forecast.

Instead of daily summer highs in the 1990s that averaged in the low to mid-80s Fahrenheit, the Eastern United States is in for daily summer highs regularly in the low to mid-90s, the study found. The study only looked at the Eastern United States because that was the focus of the funding by the Environmental Protection Agency, Lynn said.

And that's just the Eastern United States as a whole. For individual cities, the future looks even hotter.

In the 2080s, the average summer high will probably be 102 degrees in Jacksonville, 100 degrees in Memphis, 96 degrees in Atlanta, and 91 degrees in Chicago and Washington, according to the study published in the peer-reviewed journal Climate.

Dry summers to be even hotter
But every now and then a summer will be drier than normal and that means even hotter days, Lynn said. So when Lynn's computer models spit out simulated results for July 2085 the forecast temperatures sizzled past uncomfortable into painful. The study showed a map where the average high in the Southeast neared 115 and pushed 100 in the Northeast. Even Canada flirted with the low to mid-90s.

Many politicians and climate skeptics have criticized computer models as erring on the side of predicting temperatures that are too hot and outcomes that are too apocalyptic with global warming. But Druyan said the problem is most computer models, especially when compared with their predictions of past observations, underestimate how bad global warming is. That's because they see too many rainy days, which tend to cool temperatures off, he said.

There is an established link between rainy and cooler weather and hot and drier weather, said Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research. Rainy days mean more clouds blocking the sun and more solar heat used to evaporate water, Druyan said.

"I'm sorry for the bad news," Druyan said. "It gets worse everywhere."

Trenberth said the link between dryness and heat works, but he is a little troubled by the computer modeling done by Lynn and Druyan and points out that recently the Eastern United States has been wetter and cooler than expected.

Mixed reactions to study methodology
A top U.S. climate modeler, Jerry Mahlman, criticized the study as not matching models up correctly and "just sort of whistling in the dark a little bit."

But Andrew Weaver of the University of Victoria, editor of the journal Climate but not of this study, praised the paper, saying, "It makes perfect sense."

He said it shows yet another "positive feedback" in global warming, where one aspect of climate change makes something else worse and it works like a loop.

"The more we start to understand of the science, the more positive feedbacks we start to find," Weaver said.

Weaver said looking at the map of a hotter Eastern United States he can think of one thing: "I like living in Canada."

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