SuperFreakonomics on Geoengineering, Revisited

Geoengineering first came to much of the public’s attention in Levitt and Dubner’s 2009 book SuperFreakonomics. Levitt and Dubner were heavily criticized and their chapter on geoengineering was called patent nonsense, dangerous and error-ridden, unforgivably wrong and much more. A decade and a half later, it’s become clear that Levitt and Dubner were foresighted and mostly correct.

The good news is that climate change is a solved problem. Solar, wind, nuclear and various synthetic fuels can sustain civilization and put us on a long-term neutral footing. Per capita CO2 emissions are far down in developed countries and total emissions are leveling for the world. The bad news is that 200 years of putting carbon into the atmosphere still puts us on a warming trend for a long time. To deal with the immediate problem there is probably only one realistic and cost-effective solution: geoengineering. Geoengineering remains “fiendishly simple” and “startlingly cheap” and it will almost certainly be necessary. On this score, the world is catching up to Levitt and Dubner.

Fred Pearce: Once seen as spooky sci-fi, geoengineering to halt runaway climate change is now being looked at with growing urgency. A spate of dire scientific warnings that the world community can no longer delay major cuts in carbon emissions, coupled with a recent surge in atmospheric concentrations of CO2, has left a growing number of scientists saying that it’s time to give the controversial technologies a serious look.

“Time is no longer on our side,” one geoengineering advocate, former British government chief scientist David King, told a conference last fall. “What we do over the next 10 years will determine the future of humanity for the next 10,000 years.”

King helped secure the Paris Climate Agreement in 2015, but he no longer believes cutting planet-warming emissions is enough to stave off disaster. He is in the process of establishing a Center for Climate Repair at Cambridge University. It would be the world’s first major research center dedicated to a task that, he says, “is going to be necessary.”

Similarly, here is climate scientist David Keith in the NYTimes:

The energy infrastructure that powers our civilization must be rebuilt, replacing fossil fuels with carbon-free sources such as solar or nuclear. But even then, zeroing out emissions will not cool the planet. This is a direct consequence of the single most important fact about climate change: Warming is proportional to the cumulative emissions over the industrial era.

Eliminating emissions by about 2050 is a difficult but achievable goal. Suppose it is met. Average temperatures will stop increasing when emissions stop, but cooling will take thousands of years as greenhouse gases slowly dissipate from the atmosphere. Because the world will be a lot hotter by the time emissions reach zero, heat waves and storms will be worse than they are today. And while the heat will stop getting worse, sea level will continue to rise for centuries as polar ice melts in a warmer world. This July was the hottest month ever recorded, but it is likely to be one of the coolest Julys for centuries after emissions reach zero.

Stopping emissions stops making the climate worse. But repairing the damage, insofar as repair is possible, will require more than emissions cuts.

…Geoengineering could also work. The physical scale of intervention is — in some respects — small. Less than two million tons of sulfur per year injected into the stratosphere from a fleet of about a hundred high-flying aircraft would reflect away sunlight and cool the planet by a degree. The sulfur falls out of the stratosphere in about two years, so cooling is inherently short term and could be adjusted based on political decisions about risk and benefit.

Adding two million tons of sulfur to the atmosphere sounds reckless, yet this is only about one-twentieth of the annual sulfur pollution from today’s fossil fuels.

Even the Biden White House has signaled that geoengineering is on the table.

Geoengineering remains absurdly cheap, Casey Handmer calculates:

Indeed, if we want to offset the heat of 1 teraton of CO2, we need to launch 1 million tonnes of SO2 per year, costing just $350m/year. This is about 5% of the US’ annual production of sulfur. This costs less than 0.1% on an annual basis of the 40 year program to sequester a trillion tonnes of CO2.

…Stepping beyond the scolds, the gatekeepers, the fatalists and the “nyet” men, we’re going to have to do something like this if we don’t want to ruin the prospects of humanity for 100 generations, so now is the time to think about it.

Detractors claim that geoengineering is playing god, fraught with risk and uncertainty. But these arguments are riddled with omission-commission bias. Carbon emissions are, in essence, a form of inadvertent geoengineering. Solar radiation engineering, by comparison, seems far less perilous. Moreover, we are already doing solar radiation engineering just in reverse: International regulations which required shippers to reduce the sulphur content of marine fuels have likely increased global warming! (See also this useful thread.) . Thus, we’re all geoengineers, consciously or not. The only question is whether we are geoengineering to reduce or to increase global warming.


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