ANN ARBOR—An increasing number of Americans indicate that there is evidence of global warming, with 67 percent now expressing a belief that the planet has warmed over the past four decades, according to a University of Michigan survey.

It marks the highest level of belief in global warming since a 72 percent-measure in 2008 and is up from 52 percent in spring 2010.

The results come from the National Surveys on Energy and Environment, a joint effort of the Center for Local, State, and Urban Policy at U-M’s Ford School of Public Policy and the Muhlenberg Institute of Public Opinion at Muhlenberg College in Allentown, Pa.

“The only individual characteristic that reveals stark differences among Americans regarding the existence of global warming continues to be partisan standing,” said Ford School Professor Barry Rabe, director of the Center for Local, State, and Urban Policy.

“For the first time since 2008, a majority, or 51 percent, of self-identified Republicans stated that they think global warming is occurring,” he said.

The telephone survey of 998 Americans between Nov. 26 and Dec. 5, 2012, had a margin of error of 3 percent either way.

Other findings include:

In comparisons between surveys before and after the landfall of Superstorm Sandy in October 2012, the importance of hurricanes as a factor cited by individuals in their belief that global warming is happening rose significantly.

More Americans than at any time since 2008 attribute increasing global temperatures entirely to the activities of man, with over 4 out of 10 individuals stating that human activity is the cause of the change.

Among the shrinking percentage of Americans who doubt global warming’s existence, there appears to be both a decreased impact of personal experiences on their views on this subject and an increased prominence for personal religious and political factors in the determination of their doubts.

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