Thursday, August 15, 2013

Levermann on Sea-Level Rise from Climate Change

Over at RealClimate.org (here), Anders Levermann reports on recent predictive studies of sea-level rise due to global warming. The take-home conclusion from the studies is that "in total sea level rises quasi-linearly by about 2.3 metres for each degree of global warming" over the course of up to 2,000 years. Most of that sea level rise is expected to come from terrestrial ice masses (e.g., Greenland's ice). This is something that should worry us all, especially those who live in coastal regions.

I have some problems, however, with unwarranted assertions Levermann makes in his article. I first posted those problems in a comment at RealClimate.org and have decided to repeat them here:

Let me begin by saying that RealClimate.org is the best site on the web for scientifically accurate information about climate change. With respect to this posting, I do not question the findings of the studies the author cites, and I am convinced that sea level rise is a major problem that will require very expensive adaptation (not possible for all places).

Having said all that, the author goes too far in suggesting that: (a) because GHG emissions remain in the atmosphere for a very long time, they commit us to a certain extent of sea-level rise over the course of up to 2,000 years; and (b) “Society needs to decide whether we want to give up, for example, the Tower of London, or put the brakes on climate change….”

There is no warrant for the author’s implicit presumption that no technological innovations over the next 1,000 years could alter the relationship between carbon in the atmosphere and sea-level rise. Already, we have technology to reduce the terrestrial effects of GHG emissions by inserting sulfur aerosols (or other reflecting particles) into the upper atmosphere. (Whether doing so is a wise policy remains, at this point, a contested issue.)

The author’s other implicit assumption that there is no feasible way to protect a coastal (or tidal) city from the effects of sea level rise is simply false. Amsterdam has been sitting below sea level for centuries, and yet we haven’t had to “give up” on the Rijksmuseum. Whether Amsterdam can technologically work its way around another few meters of sea-level rise, remains to be seen. This is not to say that coastal areas won’t suffer grievously from climate change; sea walls may protect a city, but only at the cost of inundating other (presumably less valued) coastal areas.

The most important point, however, is that climate scientists do not make it any easier to convince skeptics (let alone deniers), when they draw the more dire, catastrophic conclusions from every study. It is far better to be parsimonious and limit conclusions to what can reasonably be inferred from the science, and leave the hyperbole to the “talking heads.”

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