A new poll finds that the percentage of Americans who believe that the climate is warming has increased in the past year, a shift in opinion that follows one of the warmest summers in U.S. history and increased debate about climate change among Republican presidential candidates. According to the Reuters/Ipsos poll, conducted from Sept. 8 to 12, 83 percent of respondents said they believe the climate is getting warmer, compared with 75 percent last year. Seventy-one percent said they believe human activities are partly or mostly to blame for climate change, while 27 percent said they believe it is the result of natural causes. Stanford University Professor Jon Krosnick said this summer’s wild weather — including prolonged heat waves, droughts in some regions, and flooding in others — is changing public opinion. He also said that discussion of climate issues during recent Republican presidential debates seems to paradoxically have caused more people to believe the climate is warming; most of the Republican candidates have attacked climate science, but Krosnick said those attacks appear to have led more Americans to think about global warming and conclude that, in fact, its is real.