A basic rule for assessing policy is to ask what bad things it makes likely or even possible. Conservatives are fond of citing the law of unintended consequences, which they know can produce negative effects dwarfing the envisioned benefits of a particular measure.
So they oppose an increase in the minimum wage for fear it will reduce employment. They oppose tax increases because those will probably inhibit growth. They are wary of same-sex marriage because it may undermine heterosexual marriage.
None of these side effects is a sure thing. But the question conservatives ask is an important one: Even if those results are not certain, is the policy worth the risk?
Dick Cheney lost few Republican allies when he explained his approach after 9/11: "If there was even a 1 percent chance of terrorists getting a weapon of mass destruction -- and there has been a small probability of such an occurrence for some time -- the United States must now act as if it were a certainty."
But this cautious approach somehow goes out the window when it comes to an issue whose ramifications span the globe: climate change. People who normally exhibit an aversion to risk are willing to behave in a way that in other contexts they would deem reckless. They put great emphasis on the immediate costs of taking preventive or ameliorative action, while largely dismissing the long-term harm from inaction.
The rationale for doing nothing to curtail carbon dioxide emissions is that there is too much uncertainty about their impact on the global climate. Never mind that the quantity of carbon dioxide in the atmosphere is up by roughly a quarter since 1960 and higher than any time in the past 800,000 years.
Never mind that the first decade of the 21st century was the warmest since record-keeping began in 1880. Never mind that in this winter of the polar vortex in the United States, last month was the Earth's fourth warmest January -- and the 347th consecutive month that exceeded the average temperature of the 20th century.
Conservatives say the climate models that predict substantial warming have "always overstated the degree to which the Earth is warming compared with what we see in the real climate," as climate scientists Richard McNider and John Christy write. The fallibility of predictions leads to the conclusion that it would be folly to put restrictions on the burning of fossil fuels.
Maybe the planet will warm more slowly than scientists predict. Maybe it will stop warming entirely. Maybe vast glaciers will slide down across the Canadian border and polar bears will invade Key West. But it's more likely that the planet will get hotter in the coming decades, particularly if carbon emissions keep rising.
That change will inevitably cause damage -- raising sea levels, expanding deserts and fostering drought. It also raises the danger that ecosystems will reach "tipping points" that generate sudden, drastic disruptions, such as ravaging the world's coral reefs or wiping out hundreds of plant and animal species.
The latter outcomes are a relatively small possibility. But small possibilities of very bad events are not to be ignored. The overwhelming odds against your house catching fire are no reason to cancel your house insurance or toss out your smoke alarms, much less lay off the fire department.
We are used to dealing with risks that are uncertain or remote by taking prudent, affordable precautions. It wouldn't take much to make a difference on this one. A carbon tax raising the price of gasoline by a mere 16 cents a gallon, increasing by 4 percent over inflation each year, would reduce emissions by a third by about 2050. It would also reduce air pollution and could be used to pay for cuts in income or payroll taxes.
Even if climate change turns out to be overblown, there's no real downside in a carbon tax. We merely would have traded a tax that reduces good things, such as work and investment, for a tax that reduces bad things, such as environmental harms and hazards. If done in a revenue-neutral way, it would more likely speed economic growth than slow it.
Maybe we can get away with doing nothing and wager that everything will be fine. But when the stakes are the fundamental health of the planet, we might want to hedge that bet.