WASHINGTON — Global warming has mostly made the weather more pleasant over the last 40 years, which may explain why many Americans don’t rank 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 study 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 weather by the end of the century, especially in the summer, the study found.

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 look at where people move, taking employment and other factors into account. It is essentially calculated on where people choose to live.

And all things being equal, the average American prefers warmer winters and less hot and humid summers. In other words, Miami, San Diego and Phoenix, which topped the chart of the new index. At the bottom: Pittsburgh, Cleveland and Detroit.

The past 40 years, America’s weather has trended more Miami than Pittsburgh.

“For the average American, the daily weather has gotten better,” Mullin said.

For 99 percent of Americans, winters have warmed by 1 degree Fahrenheit a 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 points, but climate change has other impacts. It can trigger droughts, floods and heavy rains; 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, said politics, more than weather, colors people’s perception of climate change, according to studies and surveys.