Imagine that you and a group of people want to get from the South Rim to the North Rim of the Grand Canyon. A few enterprising members of your group set forth building a ramp leading to the edge of the canyon, pointing north, and pull up in a bus, and tell you to get on. Anyone should be able to see that an effort to launch the bus will lead to a spectacular crash and burn. However, if Paul Krugman were the liberal conscience of the group he might say something like the following:

If we’re going to get real action on jumping the canyon any time soon, it will be via some version of this ramp and this bus. The bus now on the table isn’t the bus we’d ideally want, but it’s the bus we can get — and it’s vastly better than no bus at all.

Still, the bus represents major action to jump the canyon. As the Center for American Progress has pointed out, jumping the canyon would get us to the other side. And by all accounts, this bus has a real chance of being launched from our side in the near future.

So opponents of the plan to launch the bus off of the ramp have to ask themselves whether they’re making the perfect the enemy of the good. I think they are.

After all the years of denial, after all the years of inaction, we finally have a chance to do something major about jumping the canyon. Our bus is imperfect, it’s disappointing in some respects, but it’s action we can take now. And the canyon won’t wait.

Postscript:

This comment by Krugman is simply off base, and in fact opposite of reality:

Not to put too fine a point on it, think about how hard it would be to verify whether China was really implementing a promise to tax carbon emissions, as opposed to letting factory owners with the right connections off the hook. By contrast, it would be fairly easy to determine whether China was holding its total emissions below agreed-upon levels.

A carbon tax would not be applied to “factory owners” but to fossil fuel producers, with the tax applied as far upstream as possible. In both cases compliance requires counting carbon, and it is generally understood that compliance is easier with an upstream carbon tax than an economy-wide cap and trade system. There are plenty of reasons to oppose a carbon tax, but the relative complexity of compliance is not among them.