Climate change is first and foremost a threat to human society.

That fact has been somewhat obscured in regular discourse, in favor of a false dichotomy portraying climate policy as an upper-middle-class noblesse oblige idea for anxious birders and other environmentalist types, and hardheaded economists who think building up yet more wealth is more important.

In reality, one obvious way that threat to humanity is going to be expressed is through economic damage. In other words, unchecked climate change is going to be terrifically expensive.

Now, its exact cost is basically impossible to predict. Contrary to people who would confidently rely on cost damage estimates for 2100, economic projections tend to be wildly inaccurate over even five years. Furthermore, the amount of damage will depend greatly on what humans do in the future, and there have been few studies on what damage would be like under higher warming scenarios of 3 degrees or above.

But we can say the damage is going to be very large — indeed, it's already quite bad. NOAA's National Centers for Environmental Information estimates that 2017 was America's most expensive year for climate disasters of all time, with 16 disasters costing over $1 billion (more than three times the 1980-2017 average, after accounting for inflation) and a total cost of over $300 billion. That's about 1.5 percent of total GDP — or enough to pay for a $300 per month child allowance for every parent in America, with some left over.

This year is already off to a bad climate start as well. There is a severe precipitation shortfall in parts of the Southwest, with some Colorado drainages at less than 30 percent of the median snowpack. Southern California has also been rather dry — with the exception of severe rains that hammered parts of the region over the last few days, causing flooding and multiple mudslides that have killed at least 20 people.

Even the blizzard that recently struck the Northeast may have been influenced by climate change. Contrary to the notions of President Trump, who appears to believe that climate science predicts it will never be cold again anywhere at any time, it seems warming disrupts the "polar vortex," or the belt of cold air that circles around the poles of the Earth. With a weak polar vortex, frigid Arctic air can make it further south than usual — while warmer air can make it further north, leading to the paradoxical result of Anchorage occasionally being warmer than New York, or even Jacksonville.

The dramatic and rapid increase in climate damages over the last decade suggests that disasters may increase nonlinearly with warming — that is, a doubling of greenhouse gas concentrations might lead to more than twice the quantity of disasters. The only way to be sure about that is after the fact, but it's still wise to assume it might be true, due to the larger downside risk. If not, then we have decarbonized our society more rapidly than we might otherwise have. But if it is true and we don't take action, the result could be catastrophic.

Now, a few caveats are in order. First, of course we cannot say with ironclad certainty that these weather disasters are 100 percent caused by climate change, because climate change isn't the sort of phenomenon that causes individual events. What we can say is that these are just exactly the sort of weather disasters that are predicted to become more common and worse as the planet continues to warm. Don't let careerist debate pedants mix you up on this point. (And in fact, preliminary work on Hurricane Harvey found that climate change significantly increased its amount of rainfall.)

Second, expense is a highly problematic metric for measuring the overall world damage to climate change. The countries most vulnerable to climate change are generally poor, and so devastating climate disasters aren't going to show up as costing very much in dollar terms. Indeed, by far the worst disasters of 2017 happened outside the United States. As Rachel Cleetus at the Union of Concerned Scientists notes, over 11,000 people were killed by weather disasters in 2017, including 2,700 in South Asia — as against perhaps 1,400 or so in the United States (the vast majority in Puerto Rico).

Nevertheless, climate disasters really are going to be hugely expensive for the United States — and not just in dollar terms. For example, the refusal from President Trump and the Republican Congress to properly rebuild Puerto Rico has not just killed probably over 1,000 people, it has also led to a severe shortage of IV bags, no doubt killing many more.

It drives home the fact that dawdling on climate policy, as Democrats did when they had majorities in 2009-10 — or denying it's even necessary, as virtually every person of consequence in the Republican Party does — is not going to be some profitable venture. Poor countries will be hit worse, but American cities will be wrecked, much critical infrastructure will be destroyed, and many insurance companies and programs will be bankrupted. It will require endless expensive bailouts and reconstruction packages simply to stay ahead of the damage.

Conversely, the faster we move on climate policy, the cheaper it will be. The International Energy Agency has roughly estimated that every year of delay adds $500 billion to the world total of necessary investment to head off climate change. (A stitch in time saves nine, as the saying goes.)

On the most important issue facing humanity, the United States is becoming dangerously close to a rogue state. Let us hope we can soon rejoin the world community and start acting like sensible, moral adults again.