"Climate scientists believe that if the North Pole icecap melted as a result of human-caused global warming, global sea levels would rise—true or false?"
SPOILER ALERT. You'll want to answer this question before reading on.
Today's New York Times reports that 2016's Presidential contenders are further apart than they've ever been on the issue of climate change. That can't surprise many people, but it's worth pointing out how new this difference is. As recently as 2008 candidates of both major parties saw virtually eye to eye on climate today. Eight years Hillary Clinton is making climate change "the center" of her foreign policy, while Donald Trump is dismissing climate change as a hoax.
How can we differ so much on a scientific issue that most scientists consider settled? The best answer I know of is the riddle above, devised by Dan Kahan, a Yale professor of law and psychology. Kahan has presented it in surveys and found that only about 14 percent of the American public give the right answer. Liberals and conservatives are about equally likely to get it wrong.
The correct answer is false. If you don't believe me, then throw a few ice cubes in a glass of water. Make the water level with a bit of masking tape. Let the ice melt. You'll find the water level is unchanged.
The key point here is that the North Pole icecap is floating in the Arctic Ocean. It is already displacing its weight of water. Should it melt, the ocean levels will be unchanged.
Then why is there talk of Manhattan and Florida being inundated by rising sea levels? That's because there is a lot of polar ice on land, in Antarctica and Greenland. Should that melt, the water will pour into the ocean and raise the global sea level.
So much for the climate science. The icecap riddle is really about psychology. It demonstrates, first of all, that most people do not have a deep understanding of climate science. Instead they absorb a few basic bullet points, like that climate scientists (who may or may not be trustworthy, say politicians…) are always warning about rising ocean levels.
Of course, most people have strong political convictions about climate change, which they believe to be grounded in fact—unlike the other party's beliefs.
I explore the consequences of this in my book Head in the Cloud. One is that people tend to agree with the opinions of those they around them, the people and leaders they trust. Survey responses, and votes, are often expressions of community. As Kahan puts it: "Obviously, no one will answer ‘true’ when asked, ‘true or false—you and everyone you are intimately connected to are idiots?’”