Still, as a political matter, attacking scientists has limited effectiveness. It plays well with the Tea Party, but to the broader public — even to non-Tea Party Republicans — it sounds like a crazy conspiracy theory, because it is.

The second line of defense involves economic scare tactics: any attempt to limit emissions will destroy jobs and end growth. This argument sits oddly with the right’s usual faith in markets; we’re supposed to believe that business can transcend any problem, adapt and innovate around any limits, but would shrivel up and die if policy put a price on carbon. Still, what’s bad for the Koch brothers must be bad for America, right?

Like claims of a vast conspiracy of scientists, however, the economic disaster argument has limited traction beyond the right-wing base. Republican leaders may talk of a “war on coal” as if this were self-evidently an attack on American values, but the reality is that the coal industry employs very few people. The real war on coal, or at least on coal miners, was waged by strip-mining and natural gas, and ended a long time ago. And environmental protection is quite popular with the nation at large.

Which brings us to the last line of defense, claims that America can’t do anything about global warming, because other countries, China in particular, will just keep on spewing out greenhouse gases. This is a standard argument at think tanks like the Cato Institute and among conservative pundits. And, to be fair, anyone proposing climate action does have to explain how we can deal with the free-rider problem of countries that refuse to contain emissions.

Now, there is a good answer already available: “carbon tariffs” levied against the exports of countries that refuse to join in the effort to limit emissions. Such tariffs probably wouldn’t even require any change in existing trade law, and they would provide a powerful incentive for holdouts to get with the program. Still, until now, the suggestion that China could be induced to participate in climate protection was informed speculation at best.