The debate on mitigating global warming centers mostly on emissions reductions. Since I and you cause the problem by burning fossil fuels, it is reasonable to begin by considering options to remove the root cause of the problem. So far, however, our political system has failed to solve the problem.

While efforts to reduce emissions continue, it may well be that at some point, this is simply not enough. Carbon dioxide remains in the atmosphere for hundreds of years, and there are several feedback loops in the nature that could cause runaway global warming. Faced with a total catastrophe, our political leaders may have to consider more drastic measures to save the human civilization.

If we must go there, then what options remain? The alternative to emissions reductions is a collection techniques called geoengineering. Instead of reducing emissions, geoengineering techniques reduce temperatures by directly manipulating the climate.

One prominent geoengineering approach is to deflect sunlight from Earth. For instance, one could use giant satellite mirrors in the space to reduce sunlight. Alternately, one could shoot particles into the upper atmosphere for the same effect.

Another class of techniques often included in geoengineering are based on extracting carbon dioxide from the air. My Columbia colleagues, Peter Eisenberger and Graciela Chichilnisky, have founded a company to commercialize air capture.

Why do geoengineering not figure more prominently in the public debate? The proponents of geoengineering would undoubtedly blame environmentalists for dogma, and there may be a hint of truth here. But geoengineering is also an unproven approach that may (i) fail to reduce warming or (ii) produce unintended side effects. This is especially true for techniques based on deflecting sunlight, as they interfere with natural processes on a massive scale.

What is attractive about geoengineering that it does not require large economic changes. If it turns out that we fail to achieve the emissions reductions necessary to avoid rapid global warming, geoengineering may offer a politically feasible alternative. According to my Columbia colleague Scott Barrett, geoengineering is not nearly as expensive as emissions reductions. In fact, he believes it may be so inexpensive that an individual major emitter is willing to unilaterally prevent global warming through geoengineering.

But of course, individual major emitters may use geoengineering in ways that hurt other countries, so we face a governance problem — who decides on geoengineering? Additionally, the presumption that geoengineering will be inexpensive is an unproven one.

Given these problems, I would say that emissions reductions are certainly a safer bet than geoengineering for the moment. But as I said in the second paragraph of this post, this may change unless our political leaders get their act together and begin to implement mitigation policies. Like it or not, geoengineering techniques will remain on the table for decades to come. Let’s hope we will not have any use for them.

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