Projections of sea level rise continue to increase


President & Executive Director Philip B. Duffy

This subject is a good example of why I often say that the science of climate change looks more and more scary as we learn more. It has also been a personal source of frustration for nearly 10 years. I’ll return to that in a moment, but first, why has this subject come up now?

A new paper in the journal Nature finds that rapid deterioration of the Antarctic ice sheet could add more than a meter of sea level rise by 2100. That is in addition to sea level rise from thermal expansion of ocean water, melting of glaciers and melting of the Greenland ice sheet. The previous projections from the IPCC for total sea level rise range from about a quarter of a meter to a meter (by 2100), so an additional meter is a whopping big increase. (I should point out that the large range of IPCC projections is only partly due to scientific uncertainty. About half of it results from different possible assumptions about future greenhouse gas emissions.)

My frustration about this subject goes back to 2007, when the IPCC released projections of sea level rise that ignored possible contributions from rapid deterioration of Antarctic ice. This is not as crazy as it may sound—the relevant science was not well understood at the time. But in a superabundance of caution, the IPCC decided to omit this contribution entirely, which of course is tantamount to assuming that it will be zero. (Furthermore, the omission of this possibly important contribution was not made prominent.) When I squawked about this I was publicly rebuked by an IPCC co-chair.

At the time of the next IPCC report (2013), I was a White House staff member with responsibility for coordinating the US government’s scientific review of the entire report (a massive undertaking for a report consisting of thousands of pages of technically dense material). I also represented the United States in international discussions which (tediously and painfully) finalized every sentence of critical summary documents. A number of the reviewers recruited by the US government felt that the IPCC’s projected sea level rise contribution from rapid deterioration of Antarctic ice was again too low. (At least this time it was not zero!) Despite strong suggestions from our reviewers, the IPCC authors refused to budge from their insistence that this contribution would be small, and that there was little uncertainty about this. This unwillingness to fully acknowledge uncertainty displays a dismaying lack of humility (which I am happy to say is rare among scientists). Even to a non-specialist it was obvious that this science was quite uncertain. Indeed, it still is!

The good news from the Nature paper is that a large sea level rise contribution from Antarctica is not inevitable. If we rapidly reduce greenhouse gas emissions, in fact, the projected contribution is negligibly small. So, for a while at least, we have choices. If we don’t act forcefully very soon, though, irreversible physical processes will start, and our good options will disappear.

Thanks as always for your interest and support.