Filed under: Geoengineering
At roughly the same time as the Royal Society was weighing in on geoengineering last week, so was Bjorn Lomborg’s Copenhagen Consensus project, considerably less convincingly. The context here was a process by which a panel of five economists was briefed on a range of investments that might be made to do something about climate change: for each intervention there was a briefing paper and a pair of discussion papers analysing that briefing. After reading all this and hearing oral arguments the panel voted on which of the interventions was considered the best investment.
The intervention portfolio on offer featured carbon taxes of various strengths, R&D into new energy technologies, carbon sequestration and direct-air carbon capture, planning for adaptation, measures to control methane and black carbon, geoengineering of various types, forest management and expansion and north-south technology transfer. The final ranking was cloud-whitening geoengineering first, energy R&D second, aerosol geoengineering third, then carbon storage, adaptation planning, air capture, forests, methane and black carbon measures and, at the bottom, the four tax options.
Roger Pielke Jr, who was involved as one of the geoengineering discussants, comments on some of the oddnesses and inadequacies of the process on his blog. As he pointed out in his written submission to the Copenhageners (you can get all the papers involved from Lomborg’s site), the Copenhagen Consensus briefing on the costs and benefits of geoengineering, by Eric Bickel of the University of Texas, Austin and Lee Lane of the American Enterprise Institute, presented a very positive result with a rather spurious aura of accuracy. Obviously Roger’s arguments did not sway the panel, but I think they are pretty good.
The apparent accuracy comes from using a numerical model to link the economy and climate, a model called DICE developed by William Nordhaus. Bickel and Lane looked at solar radiation management (stratospheric haze or cloud whitening) with this model in the context of three strategies: doing nothing else at all, following the “optimal” abatement strategy (a strategy in which DICE sets the amount of money spent on emissions reduction so as to minimise the sum of damage done by warming, expressed in dollars, and the costs of that emissions reduction), and limiting warming to 2ºC. In all those contexts, they look at the effects of adding 1, 2 or 3 W/m^2 of cooling to other measures, if any. Much of what follows is unsurprising; the no-control world gets warmer slower with solar radiation management, and the costs of the “optimal” strategy are reduced, because there is less harm done by warming while emissions are reduced.
One result that’s worth noting is that left to itself, DICE doesn’t like the 2ºC limit at all — it is seen as more costly than doing nothing because, within the constraints of the model, the costs of emissions control are greater than the economic damage done by going over 2ºC. With just 1 W/m^2 of geoengineering, though, the situation changes: a strategy aimed at limiting temperature change to 2ºC that makes use of this relatively small amount of solar radiation management works out cheaper than either following the “optimal” path or doing nothing. As the authors put it:
This result is obtained because SRM holds temperatures in check, avoiding climate damages, while society builds the capital and technology necessary to achieve emissions reductions at lower cost. The policy lesson, of course, is that SRM can lower the costs of pursuing non-optimal greenhouse gas control strategies [such as a 2ºC temperature cap], not that non-optimal strategies are harmless.
Since, outside the world of the model, there is a pretty much sure-fire guarantee that greenhouse gas control strategies will be non-optimal (and would be even if there were any real world way of defining that optimum) that seems to me an insight worth taking away.
But in general, the paper fails to convince. The degree to which the watts per square metre removed by solar radiation management cannot really be equated with the watts per square metre added by greenhouse gases is not considered in depth, and while the authors address some of the possible indirect costs of geoengineering — rainfall pattern changes, political strife, risk of intermittency, etc — in their discussion they do not do so, as far as I can see, in their explicit numerical modelling. So they basically end up saying that the up-front costs of geoengineering look likely to be very small in comparison to the costs of greenhouse warming, which is true, but insufficient. Reading the paper you feel that doing the modelling differently, and caring about the uncertainties more, might give you a very different answer . Roger very helpfully shows that this is indeed true by pointing to an analysis by Klaus Keller and colleagues at Penn State recently submitted to the journal Climate Change. This too uses the DICE model, but with somewhat different add-ons and assumptions — as a result it gets radically different and less favourable results (pdf). This makes it hard to see the Bickel and Lee results as robust.
But though to my eyes the paper oversimplifies the issues, fails to be explicit about costs or reasonable about uncertainties, and is constrained by assumptions, Lomborg — who I have frequently enjoyed talking to and with whom I’ve agreed on at least some things in the past — contrives to put an incredibly positive gloss on the results (pdf). This is in large part because, unlike almost everyone else I’ve talked to on the matter, he seems to be happy seeing geoengineering and emissions control as an either/or proposition, rather than, at best, a both/and.
Bickel and Lane offer compelling evidence that a tiny investment in climate engineering might be able to reduce as much of global warming’s effects as trillions of dollars spent on carbon emission reductions.
First, there’s the “might”; it might — it might not. That’s why the research is needed (see below). And then there’s the willingness to ignore the other effects of carbon dioxide. If CO2 levels continue to rise unabated, with solar radiation management counteracting their warming effects, they still result in ocean acidification, massive ecological shifts towards C3 plants which will disturb many tropical ecosystems, and changes in the hydrological cycle. Bickel and Lee make the point that one should compare the hydrological changes in a model with the hydrological effects of unabated warming, which look greater. But why? Why not compare them with the effects of mitigated warming?
Ken Caldeira made the “it’s not either/or” point in a piece on the Copenhagen results in the Washington Post. He amplified his position in email to Joe Romm, who put his comments up on Climate Progress.
If we keep emitting greenhouse gases with the intent of offsetting the global warming with ever increasing loadings of particles in the stratosphere, we will be heading to a planet with extremely high greenhouse gases and a thick stratospheric haze that we would need to main more-or-less indefinitely. This seems to be a dystopic world out of a science fiction story. First, we can assume the oceans have been heavily acidified with shellfish and corals largely a thing of the past. We can assume that ecosystems will be greatly affected by the high CO2 / low sunlight conditions — similar to what Earth experienced hundreds of millions years ago. The sunlight would likely be very diffuse — maybe good for portrait photography, but with unknown consequences for ecosystems.
We know also that CO2 and sunlight affect Earth’s climate system in different ways. For the same amount of change in rainfall, CO2 affects temperature more than sunlight, so if we are to try to correct for changes in precipitation patterns, we will be left with some residual warming that would grow with time.
On top of this Bjorn seems to me to underestimate the scientific and technological uncertainties quite markedly
Many of the risks of climate engineering have been overstated. The biggest challenge is public perception. Many environmental lobbyists oppose even researching climate engineering. This is startling given the manifold benefits. If we care most about avoiding warmer temperatures, it seems that we should be elated that this simple, cost-effective approach shows so much promise.
Public perception may well be a problem for geoengineering research. But to think that it is a greater problem than the science (what do these techniques actually do? how much do they effect ocean currents/precipitation/ozone etc?) the technology (how do you spread aerosols without coagulation at just the right particle size; how do you filter seqwater well enough to pump out ultrafine sprays?) and the governance (whose hand is on the thermostat?) seems daft to me.
It’s hard not to see this sort of over-enthusiasm as at least in part a stick with which to beat greens. There may be some need for such chastisement — the “don’t even think about geoengineering” stance, while understandable as both a statement of a worldview and as a piece of practical politics, is still one to avoid. But in getting so close to the “geoengineering means we don’t have to worry” position, it seems to me that Lomborg does the current debates in the field some disservice.
Incidentally, Roger strongly recommends the analysis paper on energy R&D; I haven’t read it, but look forward to doing so.
Update: I meant to mention Alan Robock’s critique of the Bickel and Lane paper on Real Climate, but forgot.
Further update: Lee Lane responds at length in the comments
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