Remember, we have a $17 trillion economy right now, and it’s going to grow over time. So what the Chamber of Commerce is actually saying is that we can take dramatic steps on climate — steps that would transform international negotiations, setting the stage for global action — while reducing our incomes by only one-fifth of 1 percent. That’s cheap!

Alternatively, consider the chamber’s estimate of costs per household: $200 per year. Since the average American household has an income of more than $70,000 a year, and that’s going to rise over time, we’re again looking at costs that amount to no more than a small fraction of 1 percent.

One more useful comparison: The Pentagon has warned that global warming and its consequences pose a significant threat to national security. (Republicans in the House responded with a legislative amendment that would forbid the military from even thinking about the issue.) Currently, we’re spending $600 billion a year on defense. Is it really extravagant to spend another 8 percent of that budget to reduce a serious threat?

And all of this is based on anti-environmentalists’ own numbers. The real costs would almost surely be smaller, for three reasons.