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Is Climate Change Worth Tackling? A Reply To Jim Manzi.

Over at our new In-House Critics blog, Jim Manzi has written a long riposte to Al Gore on the subject of climate policy. It's a thoughtful essay that's very much worth reading in full, but if you're pressed for time, here's Manzi's conclusion: "[A] massive carbon tax or a cap-and-trade rationing system would likely cost more than the damages it would prevent." Not surprisingly, I disagree with this and want to make a few points in response.

Let me start by saying that Manzi is easily one of the smartest, most interesting conservative writers out there when it comes to global warming. Many people on the right, unfortunately, still stick to the crazed view that climate science is all a hoax. Manzi wants nothing to do with those folks. He agrees with the mainstream scientific consensus that human activities are heating up the planet and that this poses a problem (and he's taken a lot of flak from conservatives like Rush Limbaugh for staking out this position). Where he parts ways with most liberals is on just how big a problem a hotter planet will be.

Manzi bases his argument on his reading of the IPCC's 2007 Fourth Assessment Report. According to the IPCC's own estimates, he points out, a temperature rise of 4°C can be expected to reduce global GDP by about 3 percent in 2100. And on the flip side, the IPCC pegs the cost of keeping carbon concentrations in the atmosphere below a "safe" level of 450 parts per million at around 6 percent of GDP. And so, Manzi concludes, mitigation probably isn't worth it. (To be fair, he has elsewhere expressed interest in a small carbon price to fund clean-technology research, so he's not in the "do-nothing" camp.)

I see a couple problems with this argument. The first is that Manzi is clinging way too tightly to the IPCC report. Yes, the IPCC puts out the best summary of scientific knowledge about our climate system. I rely on it all the time. But the 2007 report is also dated. Climate science is a rapidly moving field, and more recent research has suggested that things may be bleaker than was projected three years ago. What's more, the 2007 report had some glaring holes in it. The panel avoided making predictions about how melting ice sheets would affect sea levels because, at the time, ice-sheet dynamics were too difficult to model. This isn't me offering up a strained reading of the IPCC's work—the 2007 report was explicit on this point. Given that sea-level rise is likely to be one of the costliest consequences of global warming by 2100 and (especially) beyond, this is a huge omission for any sort of cost-benefit analysis.

Second, it's a bit too simplistic to use a single global GDP figure when talking about the effects of climate change. True, a 3 percent drop in global GDP may not sound so bad. We'll all be much richer in 2100, we can take a hit. But that top-line figure can obscure some serious distributional issues. Climate change, after all, is expected to hit developing countries much harder than wealthier ones. And as Nate Silver once noted, you could completely wipe out the poorest 81 nations in the world, with a total population of 2.8 billion, and the blow to global GDP would "only" be about 5 percent:

From a cynical utilitarian perspective, sure, maybe it would be worth it to devastate a bunch of impoverished African countries if it makes the rest of the world richer on balance. But that raises quite a few glaring ethical questions, and I'll just note that most conservatives wouldn't leap at this trade-off in other contexts (very few on the right would support seizing property through eminent domain for the greater good of economic development, for instance).

Third point: Harvard economist Marty Weitzman has recently been arguing that there's plenty of uncertainty in climate projections, and the worst-case scenarios could be really freaking bad. Like, civilization-destroying bad. And that prospect, even if it's slim, is a great reason to cut emissions—think of pollution curbs as an insurance policy against total annihilation. In reply, Manzi accuses Weitzman of doing "armchair climate science." But that's unfair. There are plenty of actual climate scientists who are exploring these worst-case scenarios, too. A recent paper in the Proceedings of the National Academy of Sciences concluded that there's a roughly 5 percent chance that rising temperatures could render vast regions of the planet—like the eastern United States or most of India—simply uninhabitable. An insurance policy against that doesn't sound too shabby.

But Manzi then pivots to this point about worst-case scenarios:

A healthy society is constantly scanning the horizon for threats and developing contingency plans to meet them, but the loss of economic and technological development that would be required to eliminate all theorized climate change risk (or all risk from genetic technologies or, for that matter, all risk from killer asteroids) would cripple our ability to deal with virtually every other foreseeable and unforeseeable risk, not to mention our ability to lead productive and interesting lives in the meantime.

It's possible I'm misunderstanding the argument here, but Manzi seems to be suggesting that, because there's a near-infinite number of potential threats lurking out there, we shouldn't extend ourselves too far to address the big ones staring us in the face—on account of the opportunity costs. But if we followed that advice rigorously we'd end up not addressing any problems at all. Why prepare for a flu epidemic when it might impinge our ability to address a truly devastating zombie uprising? (Hey, you never know...)

The other big dispute here is over the costs of averting drastic climate change. Is Manzi right that cutting carbon emissions would "cripple our ability to… lead productive and interesting lives"? This seems awfully outlandish. I've noted before that pretty much every environmental regulation that's ever been enacted has been greeted with predictions of economic doom—yet those dire warnings have never panned out. Pollution restrictions invariably turn out to be much cheaper than expected, in part because they trigger the development of new technologies. (By contrast, nature isn't nearly so forgiving when we try to muck with it.)

But even so, there's nothing inherently expensive about climate policy. In the end, a carbon tax is just a tax. We tax lots of things in this day and age, and all of those taxes put some amount of drag on the economy. It would be a fairly simple process to replace, say, parts of the payroll tax with a tax on greenhouse-gas pollution. Why should that be crippling? Now, mind you, Congress isn't proposing a tax swap at the moment, but then again, if conservatives started rallying around the idea sincerely, maybe we could make some progress.

Update: I did a follow-up post on Manzi's argument here.