WASHINGTON -- Americans have something of a science problem. They swallow, for example, about $28 billion worth of vitamins each year, even though the Annals of Internal Medicine recently concluded that "most supplements do not prevent chronic disease or death, their use is not justified, and they should be avoided." Americans often fear swallowing genetically modified plants (and Vermont has recently required GMO content to be labeled), though GMOs have "been consumed by hundreds of millions of people across the world for more than 15 years, with no reported ill effects," according the Journal of the Royal Society of Medicine.
Other opinions are closer to astrology than science. Some deny a link between HIV and AIDS, or confidently assert a connection between cellphone usage and cancer. Rep. Michele Bachmann, during the last presidential campaign, contended that the HPV vaccine causes "mental retardation." (And, yes, about a quarter of Americans believe in astrology.)
Science has its own explanation for why people are often resistant to scientific beliefs. In evolutionary theory (assuming you believe such a thing), our intuitions about the physical world are generally accurate on a human scale -- calculating the proper force and trajectory to hit a mammoth with a spear. But on matters that are not immediately related to our survival -- say, on quantum motion, or the nature of black holes, or the effect of radiofrequency energy on the DNA in cells -- our intuitions are pretty much useless. Science has often advanced in an uphill fight against common intuitions.
These intuitions can be shaped by a variety of factors: ideology, religion, philosophy or culture. Resistance to vaccination or GMOs is sometimes rooted in a nearly religious belief that natural things are better -- including, apparently, disease outbreaks and plants that die easily in droughts. A decade ago, I met a South African health official who argued that AIDS could be treated with garlic because she believed that pharmaceutical treatment was a neocolonial plot. Resistance to evolution in America is often associated with conservative religion. And skepticism about climate change is correlated with libertarian and free-market beliefs.
Merely raising climate disruption in this context will cause many to bristle. Skeptics employ this issue as a prime example of motivated reasoning -- politicians motivated by the prospect of confiscation, scientists motivated by securing acclaim and government contracts.
In its simplest, cable-television version, this charge, at least against scientists, is outrageous. The assumption that the vast majority in a scientific field is engaged in fraud or corruption is frankly conspiratorial. In this case, the conspiracy would need to encompass the national academies of more than two-dozen countries, including the U.S.
Other, more measured criticisms ring truer. Some scientists have displayed an artificial certainty on some matters that seems to cross into advocacy. Others assume that the only way to deal with greenhouse gas emissions is a strict, global regulatory regime -- an economic and political judgment that has nothing to do with their actual expertize.
But none of these objections relates to the scientific question: Is a 40 percent increase in the atmospheric concentration of carbon dioxide since the Industrial Revolution driving disruptive warming? And further: Can this process be slowed, allowing societies and ecosystems more time to gradually adapt?
Our intuitions are useless here. The only possible answers come from science. And for non-scientists, this requires a modicum of trust in the scientific enterprise. Even adjusting for the possibility of untoward advocacy, it seems clear that higher concentrations of CO2 in the atmosphere have produced a modest amount of warming and are likely to produce more. This, in turn, is likely to produce higher sea levels, coastal flooding, shifting fisheries, ocean acidification, water shortages, lower crop yields and vanishing ecosystems. The consequences will vary by region, but are likely to be more severe in poorer nations. New York City can adapt to a rising ocean better than Bangladesh.
This scientific consensus raises difficult political questions. Is some grand global bargain on CO2 emissions, including China and India, even a possibility? Might it be more practical to make polluters pay -- perhaps with a revenue-neutral carbon tax, fully rebated to taxpayers -- thereby encouraging the development of new technologies that limit future carbon emissions? And I'd add: How can you oppose GMOs that resist pests and drought while pretending to help poor nations cope with climate disruption?
But perhaps the most difficult question is this: How can you make serious political decisions based on scientific likelihoods when politics thrives on the feeding of ideological certainties?
Michael Gerson is a columnist for The New York Times. Email, email@example.com.
By MICHAEL GERSON