Gregg Zoroya, and Doyle Rice

USA TODAY

Presidential candidates Hillary Clinton and Donald Trump are offering Americans starkly different views on global warming: Clinton sees it as an urgent concern while Trump dismisses it as a minor problem at most.

"There's never been a bigger contrast between the two candidates and the two platforms," said Tiernan Sittenfeld, senior vice president of the League of Conservation Voters.

The Trump campaign issued a statement Tuesday decrying Clinton's policy proposals on climate change as an "extreme, reckless anti-energy agenda ... to appease radical donors (who) will destroy millions of jobs and force millions more into abject poverty."

The GOP nominee said nothing about climate change in his July 21 acceptance speech at the Republican National Convention. But he told a rally in South Carolina in December that global warming was "a hoax, a lot of it," a modest change from a tweet in 2013 that called global warming "bulls---."

He has debunked climate science even though climate is likely the most thoroughly researched area on record, said Jeremy Symons, senior adviser with the Environmental Defense Action Fund.

The Democratic nominee said in her acceptance speech, "I believe climate change is real." Clinton said she was proud the U.S. had signed the Paris climate accord, which commits the world's nations to slow the rise of greenhouse gases blamed for warming the climate.

Clinton "cares deeply about protecting public health and the environment,." Sittenfeld said

The gap between the candidates has grown since the 2008 presidential election, when GOP nominee John McCain expressed concern about climate change, said Kevin Curtis, executive director of the Natural Resources Defense Council Action Fund.

Clinton's campaign website has more than 30 pages of proposals for fighting climate change. They include installing a half-billion solar panels by the end of her term and ensuring that every U.S. home is powered by renewable energy within 10 years.

Those goals are "ambitious," Curtis said. "And we think that's great. If she's elected, we'll be badgering her to do more."

Trump. by contrast, has promised to slash funding for the Environmental Protection Agency. He was asked on Fox News if global warming was caused by human activity, as most climate scientists say. "It could have a minor impact," Trump said. "But nothing, nothing to what they're talking about."

The Sierra Club issued a paper July 12 saying that if elected, Trump would be the only world leader who did not believe in the science of climate change.

"Leaders of all nations accept the scientific consensus that man is fueling climate change by burning fossil fuels and are calling for urgent action," the report states. Support comes from leaders of 195 countries, including North Korean dictator Kim Jong Un and Russian President Vladimir Putin.

"We wanted to be very clear about where Donald Trump ranks among other world leaders, and he's at the very bottom," said Michael Brune, executive director of the Sierra Club.

Trump spokesman Jason Miller responded, saying the Sierra Club "lobbies for the closure of American coal mines and celebrates the loss of countless, good-paying energy jobs for American workers."

The platforms adopted by the Republican and Democratic parties underscore the candidates' glaring differences on the issues.

The Republicans place strong emphasis on America becoming energy independent. Their platform advocates reviving construction of the Keystone XL Pipeline, which would bring crude oil from Alberta, Canada, to Nebraska, and killing an EPA plan aimed at reducing power plant emissions. It also seeks to take regulatory control away from the federal government and give it to the states.

Though it encourages the development of renewable energy sources such as wind and solar, it says it should be done entirely by private capital. It says coal is clean, an assertion that rankles environmentalists.

"It is a fantasy and wishful thinking," Symons said. "Coal kills thousands of people a year."

The Democratic platform says climate change "is an urgent threat and a defining challenge of our time" and takes dire note of rising seas, brutal drought, "superstorms," and multiplying wildfires. It argues that embracing clean energy technology will create "millions of new jobs" and cut home and business expenses.

"It's the most pro-environment platform we've ever seen," Sittenfeld said.

The Cato Institute, a libertarian think tank, calls the Democratic platform "chock full of government actions that promise to initiate, broaden and extend the current set of rules, regulations, and orders seeking to reduce ... our reliance on fossil fuels as our primary source of energy production," according to a blog post on its website.

"A Democratic administration will seek a further expansion of the reach of the federal government into our daily lives," the institute said.

Decades ago, Sittenfeld noted, environment issues enjoyed bipartisan support. The Clean Water Act in the 1970s was passed with support from both parties and signed into law by President Richard Nixon, a Republican.

Whether the sharp differences between Trump and Clinton on the issue will move voters is unclear. While the number of voters who believe in climate change has increased — including 47% of conservative Republicans — the percentage of Americans truly "alarmed" by global warming is still small, said research scientist Anthony Leiserowitz, director of the Yale Program on Climate Change Communication. He said it expanded from 10% in 2010 to 17% in a Yale Project survey released in March. The percentage of Americans who dismiss the science behind global warming has fallen from 16% to 10% over the same period.

"American engagement with this issue is at levels that we haven't seen since the latest high water mark in 2008," Leiserowitz said.