Building better concepts in climate engineering: why bother with CDR & SRM? – Patrick Taylor Smith

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I begin by offering my thanks to both Joshua Horton and Duncan McLaren for their incisive essays. One could do much worse as an introduction to issues surrounding SRM and CDR than read these two posts, and my intervention in this debate is not attempt to show that either post is false. Rather, I want to take a step back from the particulars of the conversation between Horton and McLaren and ask the following question: what is the point of drawing—or of failing to draw—a distinction between SRM and CDR? The very question, “Should we treat SRM and CDR the same or different?” presumes that there are useful categories—‘SRM’ and ‘CDR’—that ought to serve as the foundation of our analysis of geoengineering. I submit that we could easily resolve this debate if we adopted a new set of conceptual categorizations for geoengineering strategies that emphasized the relevant normative considerations for evaluating those strategies rather than by physical mechanism.

Again, what is the point of using CDR and SRM as concepts for dividing up the world of geoengineering in the first place? If we develop new concepts because carving the world up in some ways rather than others will help us protect and further our values, then it seems strange that we should prioritize the mechanism of climate system intervention in our concepts. After all, the relevant public policy and normative considerations will only be contingently related to the technical details of the relevant climate interventions. Horton is, of course, correct that SRM tends to be cheaper, faster, and riskier than CDR. Yet, it is equally clear that these are only tendencies; some SRM techniques are slow, expensive, and safe (such as painting roads and rooftops white) while some CDR techniques (such as adding base to oceans to combat acidification and aid carbon sequestration) share much in common with the fairly dangerous SRM strategies like sulfate aerosols.

The central dilemma of climate engineering, as I see it, is that we must choose between safe strategies with small effects and dangerous strategies with large effects. So, I suggest that we should structure our concepts—which would distinguish between different kinds of geoengineering—around the relevant normative considerations that generate the dilemma: the capacity to reduce, eliminate, or redress the negative social impacts of climate change and the capacity to generate negative impacts of one’s own. So, for example, we might develop a two by two set of four categories: highly beneficial with low risk, highly beneficial with high risk, low benefits with high risk, and low benefits with low risk. Each one of these categories—if they are populated by any members at all—would likely contain diverse elements, including both what are now considered SRM and CDR strategies. So, rather than initially categorizing strategies by their physical mechanism and then ask what they can do for us and how risky they are, we should instead start with the normative considerations as the foundation for our initial categorization.

We could resolve this debate if we adopted a new set of conceptual categorizations for geoengineering strategies that emphasized the relevant normative considerations for evaluating those strategies rather than by physical mechanism.

Adopting this conceptual scheme would have a host of advantages. First, it would focus our attention on what we really care about; namely, the ways in which various geoengineering strategies contribute to or undermine human values of various kinds. Second, it would bring to the foreground and make explicit needed conversations about the risks, costs, and benefits of each strategy. It would be impossible for a risky strategy to “hide” behind a technical categorization of, say, CDR to legitimate it or bypass public deliberations about its suitability. Advocates for any particular strategy would simply have to make their case—independent of whether it is SRM and CDR—about how to categorize it within the schema. Third, this new set of concepts would allow for a direct, easy, and transparent comparison between mitigation, adaptation, and geoengineering. If, as seems likely, only adaptation and mitigation strategies would be in the high benefit/low risk category, then it seems clear that there would be a strong but potentially defeasible presumption in favor of those strategies. Of course, those in favor of geoengineering would then have a straightforward dialectical burden: if they can demonstrate that some geoengineering strategies are in the ‘good’ category or categories, then so much the better for those strategies. In fact, this conceptual scheme would allow us to dispense with the notion of ‘geoengineering’ as much as CDR or SRM.

In the end, what matters is how various climate change responses impact relevant human values; their classification according to physical type—insofar as these classifications are only contingently related to those impacts—is, at best, secondary and of only indirect importance. I think we can then bypass the debate between Horton and McLaren by addressing the problematic concepts that underlie it. SRM and CDR are relatively recent conceptual innovations; there is no reason why we cannot un-invent them.

This post is part of a series.

Patrick Taylor Smith 125Patrick Taylor Smith, PhD, is an Assistant Professor in the Department of Political Science at the National University of Singapore.  He is writing a book titled “A Leap Into Darkness: Domination and the Normative Structure of International Politics,” and researches climate change and climate engineering. His papers can be found here.


The Forum for Climate Engineering Assessment does not necessarily endorse the ideas contained in this or any other guest post. Our aim is to provide a space for the expression of a range of perspectives on climate engineering.

  • Andrew Lockley

    Are we talking about physical risk? or behavioral risk? What about small-scale commercial SRM – is that big and dangerous, or small and safe? Whole concept seems to lack clarity TBH