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.