On glacial geoengineering

Jon Gertner writes in this week’s NYT magazine about John Moore’s proposals to geoengineering embayments around ice sheets in order to interrupt the destabilizing effect of warm subsurface waters on outlet glaciers. Figure 1 from Moore et al. (2018) summarizes the idea. Some thoughts.

1/ Crazy ideas are great for building and testing our understanding of the Earth system. I remember very clearly from undergraduate global biogeochemistry class with David Archer a quarter century ago his remark to the effect that ‘if you want to permanently (on human timescales) remove carbon from the atmosphere, you can’t just grow forests – you need to take your dead Christmas trees and sink them into anoxic parts of the ocean.’ As an undergraduate, that was great for helping build intuition about the carbon cycle.

(Of course, there are now start-ups pursuing exactly this strategy so I’m not sure quite what the takeaway is from the example…)

Similarly, aerosols are a major source of uncertainty in the Earth’s energy budget, and if researching solar radiation management helps us advance understanding of this term, that is for the good.

2/ If you take the cost estimates Gertner uses seriously – $50 billion to slow loss at Thwaites – the benefit-cost might work out. Thwaites as the potential to contribute about 1 m to global mean sea-level rise on a many-century timescale, though likely more like 1-4 cm over the next hundred years. Our analysis suggests a marginal present value of a 1 cm reduction in sea level through 2100 of about $10 billion. This is an underestimate, since it assumes optimal adaptation and doesn’t consider costs beyond 2100; with no adaptation, costs through 2100 are probably close to 10x higher. So the estimated benefits and costs are within the ballpark of one another.

3/ The scheme targets melting from below, which drives marine ice sheet instability. Hydrofracturing of protective ice shelves, driving by melting from above, may not be much affected. Most ice sheet models still don’t account for the combination of ice shelf hydrofracturing and the instability of resulting marine ice cliffs, which would ought to be taken into account in any modeling-based study of this concept.

4/ This critique is based purely on intuition, but I’m highly skeptical that building a massive, unique megainfrastructure project in the Amundsen Sea Embayment is only going to cost $50 billion. The Big Dig in Boston, fully connected to the supply lines of the Northeast US, cost $20 billion. Yes, it’s particularly costly to build megainfrastructure in the US, but is this crazy geoengineering scheme only 2.5 Big Digs worth in terms of cost? I doubt it.

So should we study this idea from a scientific perspective? By all means, we will learn a lot from doing so. Should we be expecting it to actually be practical? I wouldn’t.

Bob Kopp @bobkopp