Last month, the Pew Research Center released its latest poll of public attitudes on global warming. On its face, the news was not good: Belief that global warming is occurring had declined from 71 percent in April of 2008 to 56 percent in October — an astonishing drop in just 18 months. The belief that global warming is human-caused declined from 47 percent to 36 percent.

While some pollsters questioned these numbers, the Pew statistics are consistent with the findings by Gallup in March that public concern about global warming had declined, that the number of Americans who believed that news about global warming was exaggerated had increased, and that the number of Americans who believed that the effects of global warming had already begun had declined.

The reasons offered for these declines are as varied as opinion about climate change itself. Skeptics say the gig is up: Americans have finally figured out that global warming is a hoax. Climate activists blame skeptics for sowing doubts about climate science. Pew's Andrew Kohut, who conducted the survey, says it's (mostly) the economy, stupid. And some folks have concluded that Americans, with our high levels of disbelief in evolution, are just too stupid or too anti-science to sort it all out.

The truth is both simpler and more complicated. It is simpler in the sense that most Americans just aren't paying a whole lot of attention. Between

Why have Americans been supportive of action to address climate change yet so weakly committed?

being asked about things like whether they would provide CPR to save the life of a pet (most pet owners say yes ) or whether they would allow their child to be given the swine flu vaccine (a third of parents say no), pollsters occasionally get around to asking Americans what they think about global warming. When they do, Americans find a variety of ways to tell us that they don't think about it very much at all.

Three years after it seemed that "An Inconvenient Truth" had changed everything, it turns out that it didn't. The current Pew survey is the latest in a series of studies suggesting that Al Gore probably had a good deal more effect upon elite opinion than public opinion.

Public opinion about global warming, it turns out, has been remarkably stable for the better part of two decades, despite the recent decline in expressed public confidence in climate science. Roughly two-thirds of Americans have consistently told pollsters that global warming is occurring. By about the same majority, most Americans agree that global warming is at least in part human-caused, with this majority roughly equally divided between those believing that warming is entirely caused by humans and those who believe it to be a combination of human and natural causes. And about the same two-thirds majority has consistently supported government action to reduce greenhouse gas emissions since 1989.

This would be good news for action to address climate change if most Americans felt very strongly about the subject. Unfortunately, they don't. Looking back over 20 years, only about 35 to 40 percent of the U.S. public worry about global warming "a great deal," and only about one-third consider it a "serious personal threat." Moreover, when asked in open-ended formats to name the most serious problems facing the country, virtually no Americans volunteer global warming. Even other environmental problems, such as air and water pollution, are often rated higher priorities by U.S. voters than global warming, which is less visible and is experienced less personally than many other problems.

What is arguably most remarkable about U.S. public opinion on global warming has been both its stability and its inelasticity in response to new developments, greater scientific understanding of the problem, and greater attention from both the media and politicians. Public opinion about global

The lesson would appear to be that apocalyptic threats are unlikely to become priority concerns.

warming has remained largely unchanged through periods of intensive media attention and periods of neglect, good economic times and bad, the relatively activist Clinton years and the skeptical Bush years. And majorities of Americans have, at least in principle, consistently supported government action to do something about global warming even if they were not entirely sold that the science was settled, suggesting that public understanding and acceptance of climate science may not be a precondition for supporting action to reduce greenhouse gas emissions.

The more complicated questions have to do with why. Why have Americans been so consistently supportive of action to address climate change yet so weakly committed? Why has two decades of education and advocacy about climate change had so little discernible impact on public opinion? And why, at the height of media coverage and publicity about global warming in the years after the release of Gore's movie, did confidence in climate science actually appear to decline?

Political psychology can help us answer these questions. First, climate change seems tailor-made to be a low priority for most people. The threat is distant in both time and space. It is difficult to visualize. And it is difficult to identify a clearly defined enemy. Coal executives may deny that global warming exists, but at the end of the day they're just in it for a buck, not hiding in caves in Pakistan plotting new and exotic ways to kill us.

Second, the dominant climate change solutions run up against established ideologies and identities. Consider the psychological concept of "system justification." System justification theory builds upon earlier work on ego justification and group justification to suggest that many people have a psychological need to maintain a positive view of the existing social order, whatever it may be. This need manifests itself, not surprisingly, in the strong tendency to perceive existing social relations as fair, legitimate, and desirable, even in contexts in which those relations substantively disadvantage the person involved.

Many observers have suggested that Gore's leading role in the global warming debate has had much to do with the rising partisan polarization around the issue. And while this almost certainly has played a part, it is worth considering that there may be other significant psychological dynamics at play as well.

Dr. John Jost, a leading political psychologist at New York University, recently demonstrated that much of the partisan divide on global warming can be explained by system justification theory. Calls for economic sacrifice, major changes to our lifestyles, and the immorality of continuing "business as usual" — such as going on about the business of our daily lives in the face of looming ecological catastrophe — are almost tailor-made to trigger system justification among a substantial number of Americans.

Combine these two psychological phenomena — a low sense of imminent threat (what psychologists call low-threat salience) and system justification — and what you get is public opinion that is highly resistant to education or persuasion. Most Americans aren't alarmed enough to pay much attention,

Americans typically give less credit to expert opinion than do the educated elites.

and efforts to raise the volume simply trigger system-justifying responses. The lesson of recent years would appear to be that apocalyptic threats — when their impacts are relatively far off in the future, difficult to imagine or visualize, and emanate from everyday activities, not an external and hostile source — are not easily acknowledged and are unlikely to become priority concerns for most people. In fact, the louder and more alarmed climate advocates become in these efforts, the more they polarize the issue, driving away a conservative or moderate for every liberal they recruit to the cause.

These same efforts to increase salience through offering increasingly dire prognosis about the fate of the planet (and humanity) have also probably undermined public confidence in climate science. Rather than galvanizing public demand for difficult and far-reaching action, apocalyptic visions of global warming disaster have led many Americans to question the science. Having been told that climate science demands that we fundamentally change our way of life, many Americans have, not surprisingly, concluded that the problem is not with their lifestyles but with what they've been told about the science. And in this they are not entirely wrong, insofar as some prominent climate advocates, in their zeal to promote action, have made representations about the state of climate science that go well beyond any established scientific consensus on the subject, hyping the most dire scenarios and most extreme recent studies, which are often at odds with the consensus of the Intergovernmental Panel on Climate Change.

• This article was shared by our content partner Yale Environment 360, part of the Guardian Environment Network