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Global warming may have improved U.S. weather, but for how long?

A cherry blossom tree in bloom on University Boulevard in Harrisonburg, Va. (Austin Bachand/Daily News-Record/AP)

Global warming has mostly made the weather more pleasant for Americans over the past 40 years, which may explain why much of the public doesn’t consider climate change as big a threat as do scientists and the rest of the world, a new study suggests.

But that perceived benefit of global warming — mostly milder winters — will soon be outweighed by more-oppressive summer heat, according to a study in the journal Nature that’s dividing the scientific community.

“Americans are getting the wrong signal from year-round weather about whether they should be concerned about climate change,” said the study’s lead author, Patrick Egan, a public policy professor at New York University. “They’re getting the good parts and haven’t had to pay the price of the bad part.”

At least, not yet.

If heat-trapping gases aren’t controlled, nearly nine out of 10 Americans will have noticeably worse — not better — weather by the end of the century, especially in the summer, the study found.

A world transformed: Climate change’s impact around the globe

This undated photo courtesy of NASA shows Thwaites Glacier in Western Antarctica. A major ice sheet in western Antarctica is melting, and its collapse is predicted to raise global sea level nearly two feet (61 centimeters), scientists said May 12, 2014. Theories of the ice sheet's impending doom have been circulating for some time, and a study in the journal Science said the process is now expected to take between 200 and 1,000 years. The thinning of the ice is likely related to global warming, said the study which was funded by NASA and the National Science Foundation. Airborne radar measurements of the West Antarctic ice sheet allowed scientists to map the underlying bedrock of Thwaites Glacier. AFP PHOTO/NASA/HANDOUT = RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / NASA / HANDOUT" - NO MARKETING NO ADVERTISING CAMPAIGNS - NO A LA CARTE SALES/DISTRIBUTED AS A SERVICE TO CLIENTS = HANDOUT/AFP/Getty Images (Handout)

To try to understand America’s reluctance to tackle climate change, Egan and Megan Mullin, an environmental policy professor at Duke University, created a weather preference index for Americans based on past studies that looked at where people move, taking employment and other factors into account.

All things being equal, Americans prefer the weather to be warmer in the winter. In other words, Miami, San Diego and Phoenix, which topped the chart of the new index, are desirable places to live. Unlike, say, Pittsburgh, Cleveland and Detroit.

Over the past 40 years, America’s weather has trended closer toward Miami’s than Pittsburgh’s.

“For the average American, the daily weather has gotten better,” Mullin said. People like going coatless in December, as many did this past year.

For 99 percent of Americans, winters have warmed by 1 degree per decade in the winter and only a seventh of a degree a decade in the summer, the study found.

America “may have been lulled into complacency when it comes to the impacts of climate change,” said Penn State climate scientist Michael Mann, who wasn’t part of the study but called it a solid analysis. He and other scientists said the study raises interesting points, but climate change has other major effects on people. It can trigger droughts, floods and heavy rainfalls; increase sea levels; make food and water scarce; and spread insect-borne diseases.

Other scientists dismissed the study. Matthew Nisbet, who studies climate communications at Northeastern University in Boston, said it was seriously flawed. He said looking at where people live is not a good indicator of the weather that people prefer.

Nisbet and University of Oklahoma meteorology professor Renee McPherson said that, according to studies and surveys, politics colors people’s perception of climate change more than weather does.

Critics also noted that the study doesn’t deal with extreme weather such as this month’s downpours in Houston, California’s four-year drought or Hurricane Sandy. George Mason University professor Ed Maibach said surveys show that nearly 40 percent of Americans say extreme weather hit their community in the past year.

“People moved from New Orleans because of Katrina, not because they thought Houston, Dallas or Oklahoma City had better evening temperatures,” McPherson said.

Mullin and Egan said their study could not incorporate the effect of extreme weather on people’s preferences, adding that a key message is that scientists should talk more about extreme weather than average temperatures.

According to Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, which is funded by the National Science Foundation, hot summers are more of a problem than the study suggests. The fires, droughts and heat waves of a record-hot 2012 cost $75 billion. In an email, he added: “It is unconscionable to say the climate has improved when the only reason is because one can use air conditioning.”

— Associated Press