Warm Weather at Kik Pool 17_dn

Children and adults enjoys the hot sun at Kik Pool in Kalamazoo. The number of Americans who believe there is no evidence of global warming hit its lowest level in eight years, yet more Republicans are unsure that there is evidence of climate change even as 2016 is shaping up as the warmest year on record. (Daytona Niles/Kalamazoo Gazette)

(Daytona Niles)

ANN ARBOR, MI - More Republicans are unsure there is evidence of climate change even as 2016 is shaping up as the warmest year on record, a new survey shows.

The report from the National Surveys on Energy and Environment showed twice as many Republicans were unsure about evidence of global warming as they were a year ago.

Overall, though, just 15 percent of Americans say they don't believe the earth is warming, down from 24 percent a year ago and the lowest since the NSEE began in 2008.

"The rise of Donald Trump as the Republican nominee for president - a self-professed nonbeliever of global warming - may have had an impact on Republican attitudes about climate change," said Sarah Mills, a postdoctoral fellow at the Center for Local, State, and Urban Policy at the University of Michigan.

"Our survey indicates Trump's influence may have led to increased uncertainty among Republicans as opposed to a wholesale swing from believer to nonbeliever status."

The GOP nominee said nothing about climate change in his July 21 acceptance speech at the Republican National Convention. According to an article in USA Today, 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---."

Trump has referred to global warming as a hoax multiple times during speeches and on his Twitter account in recent years.

The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive. — Donald J. Trump (@realDonaldTrump) November 6, 2012

NBC News just called it the great freeze - coldest weather in years. Is our country still spending money on the GLOBAL WARMING HOAX? — Donald J. Trump (@realDonaldTrump) January 25, 2014

The survey is a joint effort of CLOSUP at U-M's Ford School of Public Policy and the Muhlenberg Institute of Public Opinion at Muhlenberg College in Allentown, Pennsylvania.

The survey found Americans' views on climate change - and the confidence with which they hold those views - has set new benchmarks.

A record 71 percent of those who believe climate change is occurring - and nearly half of all Americans - are "very confident" that there is evidence the Earth is warming. Confidence, however, also is up among those who say there is no solid evidence that the earth is warming.

"This suggests that climate change continues to be a highly polarized issue in the United States, even as the number of those who doubt its existence is decreasing," said Christopher Borick, director of the Muhlenberg Institute of Public Opinion.

The random telephone survey of 768 American adults was conducted April 5-26. The survey had a margin of error of 4 percent.