The Earth is hotter than ever this year, and so is the debate over climate change.

Average temperatures are rising at unexpectedly high rates, so much so that a limit for global warming established by world leaders at a climate summit in Paris in December is now expected to be breached in the next few decades.

But though there is abundant evidence for climate change, it still remains one of the most polarizing political issues, as the partisan divide between Americans deepens.

"It's more politically polarizing than abortion," said Anthony Leiserowitz, director of the Yale Program on Climate Change Communication, to the Associated Press. "It's more politically polarizing than gay marriage."

Surveys by Leiserowitz and his colleagues show that the number of Americans who view climate change as an alarming threat and want action now at 17 percent. Another 28 percent report being concerned, but view it as a more distant threat. On the other end of the spectrum, there's the 10 percent who reject the idea of global warming and the data behind it.

The partisan divide behind the issue is a relatively new phenomenon: in the early 2000s, Republican Sen. John McCain of Arizona was an outspoken proponent of taking action to curb climate change, and George W. Bush recognized a need to regulate carbon dioxide.

However, many Republican politicians and candidates in recent years have rejected the concept entirely. Presidential candidate Donald Trump, for one, has repeatedly referred to global warming as a "hoax."

A recent National Survey on Energy and Environment found that the percent of Republicans who don't believe climate change is real jumped from 26 to 34 percent from this past fall to this spring.

Sarah Mills, a postdoctoral researcher at the University of Michigan’s Gerald R. Ford School of Public Policy, told The Christian Science Monitor that it was one of the "most dramatic shifts we have seen," and attributed some of the jump to the political rise of Mr. Trump.

Other experts said it was unlikely that Trump was the driving force behind the numbers, telling the Monitor's Christina Beck that it was a matter of people "paying more attention to politics and to where the Republican party stands."

The US's role in combating climate change could largely depend on who is elected president in November: Trump has said that, if elected, he will pull out of the agreement made in Paris by nearly 200 countries to reduce use of fossil fuels. Hillary Clinton, the Democratic nominee, supports the Paris pact.

Already, since December, average temperatures have risen to 1.3 degrees Celsius (3.6 Fahrenheit) above preindustrial times. The goal set roughly six months ago was to only allow the temperature to rise 1.5C.

"It's hard to avoid overshoot," said Glen Peters, a scientist at the Center for International Climate and Environmental Research in Oslo, to Reuters. Now, "it's more a question of the size."

Uniting the country – and the world – may be almost as big a challenge as reducing the temperature itself. Those who doubt global warming aren't usually swayed by data or scientific explanations, experts say, so many activists and scientists have begun to take a more personal approach by building relationships with the section of the population that is doubtful but not entirely dismissive.

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The stronger the personal connections, the more likely that Americans will be able to come together to "overcome these tribal attitudes," said climate change activist Anna Jane Joyner to the Associated Press. "We really do have a lot more in common than we think."

This report contains material from Reuters and the Associated Press.