One of the biggest problems with discussing climate change is that a substantial fraction of the US public can't agree on basic facts. All indications are that the planet has warmed over the last century, yet polls have shown that anywhere from a fifth to a third of US citizens will disagree with the statement that "there is solid evidence that average temperatures on earth have been getting warmer over the past four decades." Now, a new poll gets at why people believe what they do, and finds that warm weather, and not scientific understanding, is driving acceptance.

Two schools, the University of Michigan and the Muhlenberg College, have been running a National Survey of American Public Opinion on Climate Change once or twice annually since 2008. During that time, the evidence has remained consistent: our planet is warmer than it was several decades ago. Yet public acceptance of that took a plunge from 72 percent down to 52 percent in the spring of 2010. It's now rebounded back to 62 percent. The number of people who actively disagreed with that fact was essentially a mirror image, peaking at 36 percent before dropping back down to 26 percent. These patterns have been seen in a variety of other recent polls from Pew and Gallup.

As usual, there was a large partisan divide, with Republicans roughly evenly split between accepting and rejecting the data. In contrast, only 15 percent of Democrats rejected it.

If there was anything distinctive about the poll, it was the inclusion of questions about why people believe what they do. Although this didn't contain an option for politicians, the poll did indicate that most people aren't paying attention to either the media or scientists, both of which hovered around 10 percent. In fact, among those who claim that the Earth hasn't gotten warmer, 80 percent claimed that "scientists are overstating evidence about global warming for their own interest." Even a quarter of those who accepted the evidence felt the same way. No questions were asked to identify exactly what the scientists' interest was.

So, what is driving opinions? Personal experience. Fully half of those who responded claimed to have personally experienced weather changes or temperature trends that have helped them formulate their beliefs. This includes people on both sides of the facts—follow up questions found people willing to say either that it seems just as cold as in the past, or that the past was much colder. In fact, the pollsters found that the number of people who accepted that the planet is warming was lower in the spring, after the experience of winter, than it was when the survey was conducted in the autumn.