The terrible risk management of climate change 'moderates'

Can conservative intellectuals think straight about climate change? Back in 2014, I argued that their fixation with the so-called global warming "pause" demonstrated most of them could not. After 2014, 2015, and 2016 all came in as the hottest years ever recorded, each one breaking the previous record (and the last by a huge margin), I checked back in to see whether such people — like The New York Times' Ross Douthat — had recanted and admitted their previous error. As of a few weeks ago, he had not.

Finally, Douthat has returned to the subject and admitted fault on the since-vanished pause. But he has made no change to his underlying view on climate change, still subscribing to what he calls "lukewarmism," a belief that climate change is real, humans are causing it, but it won't be as bad as the greens say. He's still wrong — and he unintentionally offers a good demonstration of why this sort of fake moderation on climate is untenable.

Like his colleague Bret Stephens, most of Douthat's column makes meta-discourse points, though at least in this instance he both admits to errors on his own part and the fact that the Republican Party is saturated with full-blown denial. But he outsources the meat of his lukewarmer case to two articles by Oren Cass.

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In both articles Cass makes two basic moves against the conventional climate hawk perspective. First, he argues that the damage from even the worst case scenarios envisioned by the Intergovernmental Panel on Climate Change won't be that bad, according to their own admissions. By way of examples, he points to the IPCC median prediction of 60 centimeters in sea level rise by 2100. That's possible to ameliorate, he argues. What's more, economic models suggest that human society will be so much richer that we'll easily be able to afford to fix the damages, even if they are very expensive.

Second, Cass argues that more extreme scenarios — higher and faster sea level rise, feedback loops leading to uncontrolled rapid temperature increase, a hidden nonlinear factor in the way climate sensitivity behaves, and so on — can't be attached to any known probability, and therefore deserve no risk weighting. One could imagine similarly bad scenarios for epidemic disease or nuclear war. "Working with a catastrophic mindset and a century-long timeline, one can construct an apocalyptic scenario from almost any problem," Cass writes. The implication is that these scenarios can thus be safely disregarded.

There is a lot more fluff in the articles, but those are the two major points. Let me take them in turn.

Cass is correct about the median sea level projection. But he does not mention that upper bound of that projection is 98 centimeters — that is, the IPCC believes there is a 17 percent chance that sea level rise will be greater than 98 centimeters. He also doesn't mention that the IPCC has a longstanding tendency to err on the side of conservative predictions, even if more dramatic ones are scientifically justified. That's probably partly why their sea level rise prediction under a business-as-usual scenario increased by about 60 percent between their fourth and fifth assessment reports.

What's more, in the years since the last IPCC report, new preliminary science has cast doubt on the report's conclusion that the Greenland and Antarctic ice sheets will take centuries to collapse. The latest measurements show melting happening faster and over more of each ice sheet. Cass's read of the science is rather Panglossian.

But it's the economic projections of future damage where Cass's views of risk really go haywire. As an initial matter, you must remember that it's possible to delete nearly half the Earth's population and only remove about 5 percent of world GDP. (Indeed, climate impacts are projected to hit poor nations much harder than rich ones.) Will nations like Equatorial Guinea or the Democratic Republic of the Congo be rich in 83 years? It's certainly possible, but I wouldn't put much money on it. And while rich countries might spend trillions on fixing them up, looking around the world today I would certainly not count on that happening automatically.

Second, if it is impossible (as yet) to attach a really solid probability to a rapid collapse of the Greenland ice sheet, it's even more impossible to attach a solid probability to what rate the economy is going to grow over the next eight decades. Cass points to a model done by Yale's William Nordhaus suggesting that climate damage will cost $20 trillion in 2100, but world GDP will be $510 trillion, so no biggie.

But as Jerry Taylor points out, other economic models have suggested damages far, far larger than that — especially if the harmful effects of climate change hit growth rates, and not just levels. Whether we'll be able to simply buy our way out of any future problems is, at a minimum, highly contestable.

More fundamentally, if we are talking risk assessment, any future economic projections are on much shakier epistemological grounds than climactic ones. (If you think climate models are off, check out the IMF sometime.) Whereas one could in principle figure out more or less for sure what is going to happen to Greenland given better data, better models, and better science, there's no way to get such certainty when it comes to political economy. Nordhaus' prediction of 2.3 percent world growth relies on continuous improvements in total factor productivity in line with earlier observations. But it could be that we'll simply hit an insurmountable technological bottleneck in a decade or two and be stuck there forever.

I don't think that will happen, but unlike the physics of carbon dioxide and infrared radiation, there is no law of nature stating that better technology and economic arrangements will always exist. And while a total stop does seem implausible, U.S. growth in real GDP per capita actually has slowed steadily since the 1960s, and dramatically so since the 2008 crisis — indeed, productivity growth was negative in 2016. Is that a new normal, reflecting perhaps a fundamental failure of innovation, as some argue? Personally I believe not; I think stagnant growth and low innovation reflects inequality and monopolization more than a failure of technological discovery.

But it sure does not look good in terms of glibly hanging the human future on trillions of imagined future dollars. And at a bare minimum, there is no possible justification for leaning on such economic projections while discarding equally uncertain but possible disaster scenarios.

In reality, you do not have to know the precise probability of a future disaster to know it's a real possibility. And the very worst future climate possibilities are bad enough that it's worth spending quite a lot to head them off. Trusting to future riches that may or may not exist is simply poor risk management.