When Rick Santorum says that scientists on the left have a concocted an elaborate hoax about climate change in order to justify increased governmental control, we're not surprised -- it's become an accepted strategy in political discourse.  But why are environmental issues so politically polarizing? Both Democrats and Republicans like nature.  And it wasn't always this way. Richard Nixon, for example, signed the Endangered Species Act and the Clean Air Act into law. But research shows that political orientation is now one of the strongest predictors of attitudes about global warming. (A lot of information about global warming beliefs is available from the Yale Project on Climate Change Communication.)

To understand the situation, we need to consider the social psychology involved.  Although you might think that attitudes are based on information, that's only a small part of it.  Few of us have the time or expertise to evaluate all the information about changes in the earth's climate.  So we start with only a subset of the available information.  And this subset is not random:  people from different demographic groups (including political ideology) get their information from different sources. There are different environmental stories on Fox News and on MSNBC. 

Beyond information, there's the question of trust. Who are we more likely to believe? Exposure to information won't change anyone's mind if the information comes from an untrustworthy source. If you truly believe that scientists have a self-serving agenda, what they say will be less influential. 

Possibly the most important aspect of attitudes in this case is the way they serve to express group affiliations.  We probably all remember (from high school, or later) occasions when a group of friends all decided that they liked a particular song, or food, or clothing style.  Agreeing that it was awesome -- and that another song was stupid -- was a way of belonging to the group. Classic research has shown that people who disagree with a group are more likely to be rejected.

The divide between Democrats and Republicans has increased in the past few decades. There are fewer areas of common ground. So opinions have become a way to express political affiliation. People don't have to think about the issue: they only have to know the official party line. That's particularly true, of course, if you're running for office and have to demonstrate your credentials.

How can we escape this situation? More classic social psychology tells us that overarching goals and values can help to neutralize intergroup conflict. Although it may not seem like it, there are plenty of things both political parties still agree on -- including affection for nature, saving money, and even the benefits of frugality. Maybe we can talk about the things that unite us as well as the ones that divide us. But don't expect much of that from political candidates, who need to define themselves by differentiation.

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