The latest version of the National Survey of American Public Opinion on Climate Change, conducted in December 2011, shows that Americans' belief in climate change is again climbing.
Now 62% of people surveyed agreed that there is "solid evidence that the average temperature on Earth has been getting warmer over the past four decades." That's a 7% increase from the spring of 2011 and 10 percentage points higher than in the spring on 2010—though still below fall 2008 when nearly three-quarters of Americans thought the planet was warming.
Looking at demographic factors such as gender, race, and education, though the exact percentages vary somewhat they are roughly in line with a two-thirds belief that the planet is warming, one quarter that it's not, and the rest note sure. However, when looked at on political party lines, more significant differences emerge.
For Democrats 78% say there is solid evidence of warming and just 15% say there isn't. Independents break down as 55% saying yes there's warming, 30% no there isn't, and 15% unsure. Going further the other way, 47% of Republicans say there is warming, 42% say there isn't, and 7% are unsure—which is doubly interesting in that when it comes to Republican politicians, at least at the national level climate change denial has become a de facto party line, however out of step that is with Republican voters.
As for why people believe that the planet is warming, personal observation is the leading factor, increasing over the past few years. Roughly half of people said that warmer temperatures or weather changes they've experienced was it.
Interestingly, despite all the past hype about the influence of An Inconvenient Truth over people's acceptance or non-acceptance of climate change, back in 2008 just 2% of people responded that the film was the primary influence (only declining species was lower). Ever since then it has dropped below 1% in influence, with observed warmer temperatures and weather changes climbing, as well as human activity all climbing.