evidence: Scientists first noted the possibility that the burning of greenhouse gases, such as fossil fuels, could increase temperatures back in the 1800s. A report from National Academy of Sciences in 1977 warned that the burning of fossil fuels could result in average temperatures increases of 6 degrees Celsius by the year 2150.2 The Intergovernmental Panel on Climate Change (IPCC), which reflects scientific opinion on the topic, stated in the forward to its 2013 report, "the science now shows with 95 percent certainty that human activity is the dominant cause of observed warming since the mid-20th century."3 And, several analyses of scholarly publications suggest widespread consensus among climate scientists on this point.4 [...] As with previous Pew Research Center surveys, there are wide differences among political party and ideology groups on whether or not human activity is responsible for warming temperatures. A large majority of liberal Democrats (79%) believe the Earth is warming mostly because of human activity. In contrast, only about one-in-six conservative Republicans (15%) say this, a difference of 64 percentage points. A much larger share of conservative Republicans say there is no solid evidence the Earth is warming (36%) or that warming stems from natural causes (48%).