Has anyone noticed that after 20 years and $25 billion in government-sponsored research on climate change, the political controversy over global warming is actually more intractable and bitter today than it has ever been in the past? Of course there are good reasons, such as the failure of the recent U.N.-sponsored Copenhagen climate conference, stubborn partisanship in the U.S. Congress, and recently discovered mistakes and distortions in the supposedly authoritative 2007 report of the Intergovernmental Panel on Climate Change. But these, like the tumors in a cancer patient, are symptoms of a mortal pathology, not its cause.

A dangerous idea has taken hold in modern politics, and the sooner it is discredited, the better. The idea is that political disagreements can be resolved by science. Its basic logic seems sensible: As good children of the Enlightenment, we should turn to science to establish the facts about problems such as climate change before deciding what policies to implement. Yet the types of things that scientists are good at figuring out don't have much to do with the types of things that politicians need to decide.

If this point seems seditiously anti-rational, consider the recent history of environmental politics in the United States. In the late 1960s and early 1970s, Congress enacted an impressive raft of laws addressing air and water quality, endangered species, pesticide use, toxic waste clean-up, and the environmental impacts of government projects. The state of scientific knowledge at that time was primitive relative to today. But the political climate was favorable, and many of the problems— like smog and burning rivers—were obvious for all to see, so the science was more than sufficient to support action. Laws were passed, regulations were promulgated, and environmental protection was advanced. Four decades later, scientific understanding of the environment has improved immeasurably, while political action has become almost impossible. More knowledge has created more uncertainty about what works and what doesn't, about what's a problem and what isn't, and has given more ammunition to competing positions on issues ranging from protection of endangered species to regulation of toxic chemicals in the environment.

The most wonderful illustration of this mismatch between what science can tell us and what politicians care about is the effort to build a long-term storage site for nuclear waste at Nevada's Yucca Mountain. It's probably fair to say that, after 25 years and $13 billion of government-funded research, no area of ground on Earth is more studied than Yucca Mountain, yet all of this science has done absolutely nothing to quell opposition from locals and environmental groups. On the contrary, it provided a continual source of new discoveries and uncertainties that combatants could draw upon to bolster their political and legal cases. For example, varying estimates of the amount of ground water flowing through the rocks at the site were central both to claims that Yucca Mountain was safe and that it should be abandoned.

What makes Yucca Mountain such a political quagmire is not the complexity of the science but the way that Congress rammed Yucca Mountain down Nevada's throat in 1987—an exercise in top-down power politics that provoked profound and unquenchable resentment. So when President Obama suspended work on the site last year, he was responding not to the weight of scientific evidence but to the political weight of Senate Majority Leader Harry Reid of Nevada and the crucial electoral votes that Nevada had provided in the 2008 election.

It turns out that science contributes most to politics when nobody really cares that much about it. Consider the chemical Bisphenol A. Research on the health effects of this common component of plastic suggests a probable link to neurological damage in fetuses and children. Yet remaining uncertainty is more than sufficient to fuel protracted debate about the chemical's safety. In the meantime, many companies that use BPA in consumer products like plastic bottles and canned foods are now voluntarily trying to reduce or eliminate their use of the chemical. Why? Because smart public health activists have focused private-sector attention on the risk of consumer backlash against products that might harm children, and because cost-effective alternatives to BPA already exist. What's particularly interesting about this story is that manufacturers are taking action even as the U.S. government continues to fund research that's supposed to be the basis for regulatory action sometime in the future. The lesson from BPA is that getting the politics right is much more important than improving the science.

When people hold strongly conflicting values, interests, and beliefs, there is not much that science can do to compel action. Indeed, more research and more facts often make a conflict worse by providing support to competing sides in the debate, and by distracting decision-makers and the public from the underlying, political disagreement. In such cases each side will claim to have the scientific high ground.

Writing in the New York Times last week, Al Gore made exactly this point about climate change by noting that "the science has become clearer and clearer." Yes, there is a robust scientific consensus that human activity is causing the atmosphere to warm up. But so what? Decision-makers need to know how climate change will affect specific political jurisdictions, and, more importantly, what types of interventions will make a difference, over what time scales, at what costs, and to whose benefit—and whose detriment.

 When it comes to questions like these, political beliefs can map nicely onto different ways of selecting, assembling, and interpreting the science. If you believe that government should intervene in markets to incentivize rapid reduction of greenhouse gas emissions, you can justify your preference with data, theories, and models that predict increases in extreme weather events such as hurricanes, droughts, and floods. And if you believe, as do many conservatives, that government intervention in markets and in social arrangements should be kept to a minimum, you can find factual support for your views in the long-term unpredictability of regional climate behavior, the significant economic and social costs associated with shifting to more expensive energy sources, and the historical failure of government efforts to steer large-scale social and economic change.

Politics isn't about maximizing rationality, it's about finding compromises that enough people can live with to allow society to take steps in the right direction. Contrary to all our modern instincts, then, political progress on climate change requires not more scientific input into politics, but less. Value disputes that are hidden behind the scientific claims and counterclaims need to be flushed out and brought into the sunlight of democratic deliberation. Until that happens, the political system will remain in gridlock, and everyone will be convinced that they are on the side of truth.

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