I have a big tent policy when it comes to global warming. I’m a long, long way from being an expert, so I’ll take anyone’s opinion seriously, even if they are widely suspected of being ideological or partisan hacks. Which is my back-handed way of saying that I’m about to take Paul Krugman seriously, even though I would only do so under exceptional circumstances. Here’s the opening graf from his cover story in the NYT Magazine:

If you listen to climate scientists — and despite the relentless campaign to discredit their work, you should — it is long past time to do something about emissions of carbon dioxide and other greenhouse gases. If we continue with business as usual, they say, we are facing a rise in global temperatures that will be little short of apocalyptic. And to avoid that apocalypse, we have to wean our economy from the use of fossil fuels, coal above all.

The word “apocalypse” is not accidental. Krugman writes,

As Harvard’s Martin Weitzman has argued in several influential papers, if there is a significant chance of utter catastrophe, that chance — rather than what is most likely to happen — should dominate cost-benefit calculations. And utter catastrophe does look like a realistic possibility, even if it is not the most likely outcome.

I find it somewhat ironic that Krugman considers worst case scenarios to be the basis for major policy initiatives. It is not a flawed argument, but it is strangely reminiscent of worst case scenarios involving Saddam Hussein’s arsenal of WMD. Not surprisingly, political commitments may determine how one assesses the probability of improbable scenarios. So we have to argue about which worst case scenarios are probable enough to justify pre-emptive action.

Krugman pitches his article as a primer for the intelligent layman on the science, politics and economics of reducing carbon emissions. That being the case, I think it’s fine for Krugman to argue via assertion that average temperatures have risen noticeably over the past few decades. But Krugman never really explains why we should have so much confidence in predictions of what global temperatures will be like in 2050 or 2100. His basic answer is to trust the scientists:

The fact that climate modelers more than 20 years ago successfully predicted the subsequent global warming gives them enormous credibility.

I’m certainly willing to grant them a lot of credibility, even after the ClimateGate shenanigans, but I’ve got to know more details before I accept that 20 years of good predictions are the natural prologue to 100 years of good predictions.

The biggest assumption in Krugman’s article may not be about science, however, but about politics. He recognizes that reducing carbon emissions will only work if the biggest emitter of all — China — embraces the system. Why does Krugman believe that is likely?

For those who think that taking action is essential, the right question is how to persuade China and other emerging nations to participate in emissions limits. Carrots, or positive inducements, are one answer…

But what if the Chinese (or the Indians or the Brazilians, etc.) do not want to participate in such a system? Then you need sticks as well as carrots. In particular, you need carbon tariffs.

A carbon tariff would be a tax levied on imported goods proportional to the carbon emitted in the manufacture of those goods. Suppose that China refuses to reduce emissions, while the United States adopts policies that set a price of $100 per ton of carbon emissions. If the United States were to impose such a carbon tariff, any shipment to America of Chinese goods whose production involved emitting a ton of carbon would result in a $100 tax over and above any other duties. Such tariffs, if levied by major players — probably the United States and the European Union — would give noncooperating countries a strong incentive to reconsider their positions.

To the objection that such a policy would be protectionist, a violation of the principles of free trade, one reply is, So? Keeping world markets open is important, but avoiding planetary catastrophe is a lot more important.

I’m no more of a China expert than I am a climate scientist, but I’m pretty sure that carbon tariffs — or even the threat of carbon tariffs — would enrage China. My best guess is China would prefer an all-out trade war to a carbon tariff.

This possibility causes a lot of trouble for one of Krugman’s other main arguments, namely that reducing emissions won’t be that expensive, or at least much less expensive than doing nothing. If we have to threaten a trade war with China, there’s no way around expensive — which is precisely why neither the US nor the European Union is likely to ever impose a carbon tariff, or even threaten to impose one.

Criticism aside, I did find Krugman’s article informative. It is also even-tempered, unlike the column in which he denounced Republicans for treason against the planet. So go read it.

Cross-posted at Conventional Folly

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