In a similar study, we asked Democrats, Republicans and independents in Washington State to consider a carbon tax that was on the ballot in their state in 2016. There, we mentioned either liberal Democrats (like the Green Party of Seattle) or conservative Republicans (like the former secretary of state George Shultz) who in fact supported the initiative.

We found, in both studies, that our participants toed the party line. Republicans supported climate policies that they understood to be backed by Republicans and were neutral toward policies backed by Democrats. Democrats supported policies that they understood to be backed by Democrats more than they supported policies backed by Republicans.

Why is it so important to people whether climate policies are proposed by their own party or the opposing one? An interesting suggestion from our research is that Democrats and Republicans are swayed by partisanship because they think their fellow Democrats or fellow Republicans are even more swayed by partisanship — and they don’t want to break ranks.

We discovered this when we asked people to estimate how their fellow citizens would respond to the policies. People overestimated how much Democrats and Republicans opposed policies backed by the other side. Furthermore, these exaggerated estimates turned out to strongly predict their own support for a policy.

This finding did not come as a total surprise. Among social psychology’s fundamental lessons is that people are profoundly affected by what other people think. In their desire to be upstanding members of their political tribe, people are pulled toward embracing the stances of their peers and loath to publicly disagree with them.

As a result, the actual degree of political polarization on climate change belief and support for climate policy is considerably less than people think it is. Environmental activists often seek to increase support for climate policy by convincing skeptics about the reality and urgency of climate change. But our studies suggest that climate policy gridlock is largely about exaggerating disagreement for the sake of disagreement.

Fortunately, there is some cause for optimism. Our studies revealed a consistent, if somewhat surprising, pattern: Political disagreement was substantially smaller when it came to Republican-backed policies.

In particular, there was very little distance between Republicans and Democrats when evaluating a Republican-proposed carbon tax. This suggests that a carbon tax such as the one proposed by prominent Republicans including James Baker III and Mr. Shultz may hold more promise for bipartisan agreement than we have seen with Democratic policies in the past.