Schelling on solar radiation management

What if it works too well?

As one of Tom Schelling’s grad students, I still have the privilege from time to time of seeing him in informal settings, and I almost always carry away something of value. With his permission, I offer a report on his latest thoughts about what is called “geo-engineering” as a response to the impending global warming crisis.

The bottom line: he’s fairly confident that solar radiation management (SRM), in the form of the release of sulfates into the stratosphere, would work to substantially offset the increase in global mean temperature that would otherwise result from the likely trajectory of greenhouse-gas releases; that it would work quickly; that the cost would be manageable; and that the side-effects of the sulfates would be tolerable.

But this might not, in his view, be anything like undiluted good news. SRM does nothing to cure the other impacts of increased carbon dioxide concentrations, and in particular the acidification of seawater. (The Coca-Cola Company was not the first to discover that if you dissolve carbon dioxide in water you get carbonic acid, aka seltzer.) So the danger is that the efficacy of SRM to deal with the warming crisis will slow the effort to control carbon dioxide emissions. As Schelling put it, “the danger is that solar radiation management could work too well and too cheaply.”

Schelling has been applying his own orthogonal-to-everyone-else style of analysis to the global warming issue for nearly two decades.

Before the opponents of restricting greenhouse-gas emissions settled on the tactic of sticking their fingers in their ears and their heads in the sand and simply denying that the problem was real, their favored tactics were to plan for mitigation of consequences (e.g., dike-building) or try to reduce the consequences of GHG release either by recapture (carbon sequestration) or reducing the flux of solar energy so as to control warming even in the face of increased greenhouse effects (solar radiation management). These last two options are in the portfolio called “geo-engineering.”

Schelling, undeterred as usual by the risk of being seen in bad company, urged that we take both mitigation and geo-engineering seriously. He was also open to the possibility that improved modeling would reduce the expected impact of GHG build-up both on global mean temperatures and on the side-effects of warming in the the form of floods, droughts, storms, etc. That, plus doubts about the feasibility of negotiating and enforcing any sort of global deal on GHG emissions, led him to push for what he called “no-regrets” policies: all of the pure-win options such as improving energy efficiency that would pay for themselves even if global warming turned out not to be a major threat.

Now that improved modeling has mostly served to increase the expected climate change as the result of any given level of GHG, Schelling is no longer in the “no-regrets” camp, and puts limited trust in mitigation in the face of the changes that now seem likely unless something major is done to reduce the change in global mean temperature. But he’s still skeptical that GHG emissions can actually be reduced by anything like the required amount, so “geo-engineering” is looking more and more relevant.

Carbon sequestration – capturing carbon dioxide from the atmosphere and taking it out of circulation for long periods – may be feasible, but under any technology now in sight it would be terrifically expensive. (It’s not clear that coal remains economically competitive even with current solar-electric generation if you add the cost of sequestration to the cost of production.)

Solar radiation management, by contrast, is reasonably cheap, with annual costs to offset the estimated 2050 level of GHG running in the low-to-middle eleven figures (tens of billions of dollars per year), which is after all pretty much chump change against a world GDP in the tens of trillions. That’s certainly far lower than any reasonable estimate of the costs of reducing emissions instead.

The current front-runner is sulfate release into the stratosphere. (Jet airplanes already do some of this.) The amount of sulfate in the stratosphere required to offset the temperature effects of the estimated 2050 GHG level would be about 2% of the amount of sulfate currently released each year into the lower atmosphere, so the contribution to acid rain would be negligible. The half-life of stratospheric sulfates is estimated at about a year – long enough to make the policy affordable, short enough to make it reversible.

The result would be a reduction of about 1% in the amount of solar energy reaching the surface; not very large compared to natural solar-cycle variations, though possibly perceptible to the naked eye and doubtless important to some species.

What seems crucially important to me is that SRM could be deployed quickly and have quick effects: the model is the volcanic explosions that occasionally cool the planet by a couple of degrees C for a year or two. That means that, if current models are too optimistic and Inconvenient Truth-like effects impend – rapid melting in Antarctica leading to rapid and potentially self-reinforcing rises in sea level, a shutdown of the North Atlantic Convector leading to massive cooling in Western Europe – SRM could be put in place on an emergency basis.

Again, the problem is that managing global temperature, and the side-effects of global temperature changes, is only a part of the issue. Ocean acidification is the most dramatic, but not the only, consequence of increasing the amount of carbon dioxide in the atmosphere. So insofar as the existence of SRM as an option reduces the urgency with which citizens and political leaders address the problem of carbon dioxide buildup, the result could be a cool planet with fizzy oceans and not much marine life.

Naturally – this is Kleiman speaking not, not Schelling – when the “small government” loons get out of global-warming-denialist mode, they will naturally strongly prefer the SRM option to any sort of carbon controls: regulations, taxes, or cap-and-trade. This will be especially true of the propeller-head techno-optimists who think that every problem has an engineering solution.

But I predict that they mostly won’t get their way. When one side of a debate denies the existence of a problem, it has (deserves) a hard time getting its preferred solutions to the purported non-problem taken seriously. That was the fate of much liberal thinking about crime control; once you’ve announced that “crime” is a made-up problem and that crime control is just a cover for racism, why should anyone pay attention to you when you announce that you know how to control it?

As poetically just as that result would be, and as helpful it would be to the cause of controlling carbon dioxide buildup rather than only its most dramatic bad consequence, it might lead to disaster. Because the fact remains that emissions controls are both expensive and slow-acting. If we ever find ourselves confronted with a real warming crisis, SRM may be not our best option but our only option. It seems to me only prudent to do the R&D now that means we have it available when and if we desperately need it.

As to the objection that SRM would have unknown consequences: Sure it would. So would uncontrolled warming. And so, for that matter, would the substantial-to-drastic increases in worldwide energy prices required to stop continued carbon dioxide buildup. The principle of not taking very large risks unnecessarily – the sane version of the precautionary principle – does not mean that you shouldn’t jump out of the way of an oncoming train until you’ve made a careful estimate of how badly you might get hurt when you land.

Author: Mark Kleiman

Professor of Public Policy at the NYU Marron Institute for Urban Management and editor of the Journal of Drug Policy Analysis. Teaches about the methods of policy analysis about drug abuse control and crime control policy, working out the implications of two principles: that swift and certain sanctions don't have to be severe to be effective, and that well-designed threats usually don't have to be carried out. Books: Drugs and Drug Policy: What Everyone Needs to Know (with Jonathan Caulkins and Angela Hawken) When Brute Force Fails: How to Have Less Crime and Less Punishment (Princeton, 2009; named one of the "books of the year" by The Economist Against Excess: Drug Policy for Results (Basic, 1993) Marijuana: Costs of Abuse, Costs of Control (Greenwood, 1989) UCLA Homepage Curriculum Vitae Contact:

19 thoughts on “Schelling on solar radiation management”

  1. Mark:

    I had a similar discussion with Tom a couple of weeks ago at dinner during a conference. He was more or less predicting that, over the next 20-30 years, mitigation would be insufficient (because of unresolved collective action problems) to prevent significant levels of warming, and that SRM would be deployed as a stop-gap measure. As usual, I find the expected value of disagreeing with Tom to be approximately zero.


  2. "Inconvenient Truth-like effects impend – rapid melting in Antarctica leading to rapid and potentially self-reinforcing rises in sea level, a shutdown of the North Atlantic Convector leading to massive cooling in Western Europe"

    Gore didn't say this – he can be fairly criticized for not giving a time frame, but he also didn't claim a rapid time frame.

    Sulfate shielding will reduce precipitation – did Schelling address this issue?

    Sulfate shielding cools the globe evenly while the Arctic suffers disproportionately. You must choose between modest cooling that balances global warming at the price of significant Arctic warming, or overcooling the globe to get the Arctic to the desired temperature.

    And of course there's the issue of having to maintain the shield forever by the human time scale. The quick rate that sulfates come out isn't necessarily a feature.

    So, I question Schelling's conclusion, but we may need to do it anyway.

  3. Whether human life as we know it can survive a large increase in acidification of the ocean (there's really only one) is far from clear. There's a lot of life in that space (about 99% of the volume of livable – to something – space in the world is in the water, and 90% of life forms), and life on earth depends heavily on it. Life in the ocean could carry on without life on earth, but the reverse is not demonstrated.

  4. "This will be especially true of the propeller-head techno-optimists who think that every problem has an engineering solution. "

    I'd rather be a propeller head techno-optimist, than one of the goofballs who think that every problem has an international agreement solution. You can at least point to cases of engineering solutions working…

  5. Brett – Can you give an example of a global engineering project of comparable scale? The only example I can think of of a similar scale problem is the ozone hole. Addressed, apparently successfully, by international agreement.

  6. I am sure you are right about the people who got it wrong loosing credibility. That is why the neo-cons who led us into Iraq are no longer seen as commentators on national TV and why the Republican’s economic policies have left them so far behind coming into the election. We finally have an electorate that sees through the spin and cares only about substance.

  7. Foster, that's the nice thing about engineering: It's actually based on physical laws that scale. You build a road, you can build a highway system. Now, I'll grant you, the scheme might not work due to, say, the global climate models being wacked out. But is that really a place people complaining of global warming want to go? 😉

    Anyway, a few notes;

    First, the main reason these schemes have, so far, been based on the use of sulfates, is just that sulfates are what volcanoes inject into the upper atmosphere. If it were actually implemented, there's a good chance some better particulate to inject would be found.

    Second. Ocean acidification is indeed a problem apart from warming. I bet we can find a geoengineering scheme to deal with that, too. Maybe seeding the oceans with antacids…

    Finally, any geoengineering scheme like this has winners and losers, places which will have their climate improve, places which will have their climate worsen. Do you really imagine this isn't true of geoengineering by CO2 injection into the atmosphere? Or geoengineering by it's deliberate cessation? There are places which *benefit* from global warming. There are places which would be *harmed* by it's being averted. This is among the reasons why anything approaching global unity on the subject is highly unlikely. But it's also why 'there would be losers' isn't all that much of a slam against geoengineering. There are losers with what YOU want to do, too. Try not to pretend otherwise, when you're arguing against geoengineering.

  8. Does Schelling have a take on the international politics of this? I´ve been lecturing the scenery for a while that geoengineering is world government, de facto or de jure.

    The USA is certainly technically capable of going it alone, but then it would be politically liable for the consequences – and there is a big risk of these going seriously wrong (failing monsoon, millions dead, etc.). Against a background of things going badly wrong anyway, geoengineering will also be blamed for things it didn´t cause. Revenge ecoterrorism, anybody? So the USA would need protective cover, as a minimum a UN Security Council resolution.

    The USA also needs to think about its reaction to a consortium of other countries planning to go it alone. Perhaps including Pakistan if the Himalayan glaciers start to collapse rapidly instead of slowly.

    Welcome to the world Exxon made.

  9. The post doesn't discuss the expected side effect of SRM. This is based on serious modelling by the Ken Caldeira group. They predict that SRM would caused reduced precipitation in India and China. To me this is clearly a very serious issue.

    I am a propeller head and fan of SRM (actual proposals are no where near as crazy as my personal ideas). Still, you know, from the strictly human point of view, precipitation in India and China is pretty much the most important aspect of climate.

    I notice you haven't been pushing your send agricultural junk down the mississippi and sink it below the thermocline proposal lately. I wish I'd thought of that one.

  10. I think that biosequestration is competitive with abatement. It works out to about equally costly given the current price of a European C02 permit, the cost of shipping across the country to a desert and the cost of the cheapest marketed wood product (you know the sawdust and glue stuff they try to sell you). It seems to me that it would be a big win if the plan was to ship cellulosic trash to a nearby desert.

  11. I think, contra your snark, that climate scientists are quite aware of the uncertainties in their models. That in particular is a reason to be very cautious about more geo-engineering to counter the CO2 based alteration taking place.

    I suppose you have heard the song 'There was an old lady who swallowed a fly'? If the choice is to swallow the spider, I'll first choose not to swallow the fly, thank you very much.

    Seeding the oceans with anti-acid – that is crazy talk however.

  12. Although it would "only" cost a few tens of billions of dollars a year to get sulfate aerosols into the upper atmosphere in a controlled fashion, when was the last time a single global initiative spending tens of billions of dollars a year (plus the capital costs of building the fleet of whatevers to get the sulfates up there) stayed together for 30 or 40 years?

    Much of the data we have on the effects of sulfate aerosols on temperature come from single-event massive injections of material into the upper atmosphere. Much cheaper. If I were going to be around I would bet the solution would ultimately be something like reopening Sudbury.

  13. Mobius, seeding the ocean with antacids isn't just crazy talk, it is Wile E. Coyote-worthy proposal.

    Most antacids are carbonates or bicarbonates, XHCO3 + H2O -> X+ + HCO3- + H2O H2CO3 + OH-. The carbonic acid component can (and does) gas off from solution into the air, which is precisely the the thing we're trying to avoid: atmospheric carbon dioxide.

    If you want to geo-engineer the soda pop ocean problem, you need some form of alkali to add directly, like sodium or potassium hydroxide. Of course, that reaction also drives carbon dioxide back into the atmosphere. Of course, this does have the advantage that we're at least not adding more CO2 to drive into the atmosphere.

  14. Dennis, I was merely thinking of sheer scale, rather than the specific chemical reactions. Dumping tons of alkaline muck into the oceans is just impractical based on the sheer tonnage.

    Perhaps what we need is to create a plankton that has alkaline waste, and seed the oceans with that. That could never go badly.

  15. I wonder what the relationship between 1) required global sulfate emissions and 2) accelerating emissions of greenhouse gasses from thawing tundra will look like.

    It will eventually become evident that the smart thing to do was to stop burning stuff for energy. Too bad about the horsemen.

  16. IIRC, the Royal Society looked at what would be needed to directly counter oceanic acidification, and concluded that it was not doable.

  17. Dennis, it may come as a shock to you, but there are common "weathering" reactions which consume CO2. They're one of the normal CO2 sinks in the environment, after all. Silicate minerals are not exactly in short supply, and we might achieve a twofer by using them as particulates to reduce sunlight, AND sequestrate CO2 by their accelerated weathering. (Due to the vast increase in surface area from being reduced to that fine a powder.)

    It's at least worth exploring.

  18. Geo-engineering is a pipe dream. Pump tens of billions of dollars worth of sulfates into the stratosphere every year – indefinitely? Unsustainable, obviously.

    In the end, we'll need to do what we (as life forms) have always done – adapt. Global climate has gone through more severe changes than those predicted by global warming models. Life adapted. I'm more interested in discussing how we might adapt than how we might temporarily stave off some of the ill effects for a relatively short period of time.

  19. Curing cancer is a pipe dream. We just need to adapt to the carcinogens in our environment.

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