 In the first month of 2015, the U.S. Senate voted on a proposition. This wasn't to do with taxes or regulation. They were voting on whether human activity significantly contributes to climate change. The Senate were voting on scientists' understanding of science. Did they accept the science of the greenhouse effect, which has stood the test of time for over 150 years? It turns out around half of them didn't. 49 out of 99 senators voted that global warming wasn't caused by humans. Compare that to the opinion of the scientific experts. 97% of climate scientists agree that humans are causing global warming. There's a huge gap between what the scientific community thinks and what the country's leaders think. What do the public think? Scientists from Yale University and George Mason University conducted a survey called the Six Americas Reports. The report divides the U.S. public into six groups. One group, the dismissives, don't believe global warming is happening. But only 13% of the public were dismissive about global warming, a small fraction of the public. A similar investigation in a public opinion about climate change in Australia was conducted by Zoe Leverston from the CSIRO and her colleagues. But they didn't just survey what people thought about climate change. They also examined what people thought, other people thought about climate change. Their survey divided the population into four groups. First, those who believe that global warming was caused by humans. Second, those who believe that global warming was natural. The third group believed that global warming wasn't even happening. And a fourth group didn't know what was happening. Let's have a closer look at the group who didn't believe global warming is happening. They make up only 7% of the population. But Leverston and her colleagues found something interesting in their survey data. If you ask this 7% how many people share their views, they think about half of the public don't believe global warming is happening. The small group who deny global warming think that they're a much larger group than they really are. This is known as the false consensus effect. What Leverston found in the survey data was that the group denying global warming, the group that showed a high false consensus effect, were less likely to change their opinions. It's very difficult changing the mind of someone who denies global warming. Let's look at another part of the Australian public. The 45% who think humans are causing global warming, when that group of 45% were asked, how many other Australians share their view, they estimated only 40%. In other words, they underestimated how many people share their view. So why this pattern of overestimation and underestimation? Well, here's a somewhat problematic statistic that might provide some clues. Let's go back to the 7% who don't think global warming is happening. When you ask the general public, what percentage of the population believe global warming isn't happening, they think it's around 23%. That's more than three times the actual 7% who deny global warming. The general public tend to overestimate the amount of doubt among the community about climate change. This is called pluralistic ignorance. Most people accept climate change as real, but they assume there are a lot more people denying climate change than they really are. How does this happen? A vocal minority can seem bigger than they really are. By being very vocal, a small minority can have a disproportionate influence on the rest of the public. This is particularly the case when the mainstream media give minority-contrarian voices a megaphone. Look at how network television covers climate change. Only 28% of media coverage paint an accurate picture of climate science. This and a number of other studies find that climate denial receives media coverage that is out of proportion to the percentage of people who hold those views. What happens when the media give climate science denial equal weight with climate scientists? Here's data that I've collected to answer that question. The left bar shows what people think the consensus is if they've not shown any media coverage about climate change. The right bar shows perceived consensus after they've shown some media coverage that gives contrarians equal weight with climate scientists. Just reading one article with false balance significantly decreases perception of scientific agreement. So even if climate science denial is held by only a small proportion of the public, the research tells us that we can't ignore denial. A small vocal minority can have a large influence out of proportion with their actual size. Misconceptions that arise from denial can confuse the public and giving contrarians equal weight with scientists confuses the public about the state of scientific consensus. That means it's necessary to respond to climate science denial. How we respond should be informed by scientific research.