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#GettingWorse: Sea level rise edition

29 May 2024 | Science Notes

It’s not that sea level rise (SLR) itself is getting worse. Probably not, at least. What is getting worse are the excuses for government experts continuing promoting extreme high end SLR scenarios. So for this week’s entry in our series we turn to a Substack essay by the Breakthrough Institute’s Jessica Weinkle who reviewed the evolution of the projected SLR range produced by multi-agency groups in the US government between 2012 and 2022. As Weinkle states, “The scenarios have not actually changed much since 2012. Rather, what has changed is their justification which has become increasingly untethered.” As in the high-end scenarios are still being pushed even long after the rationale for them got washed away by the morning tide.

Since we’re discussing reports from the vasty deep of the US administration, we should explain our belief here at CDN that when a government report is being produced, paradoxically, the more agencies and people are involved the less quality control takes place. With more people on the author list there is more opportunity for a few people committed to extreme views to dominate the editing process, especially because the less zealous authors tend to assume that, as it approaches its final draft, the report will be checked by lots of their colleagues so they need not bother. Shirking gets easier the more people whose efforts you can freeload on. So we have much less confidence in the conclusions of a 700-page assessment prepared by a 10-agency consortium than we would in a brief report written by Sam and Pete down at the weather office.

Weinkle’s paper reinforces this belief as she discusses four SLR reports produced in 2012, 2016, 2017 and 2022. The 2012 report was prepared as part of what would eventually be the 2017 US National Climate Assessment, and it projected a wide range of SLR possibilities between 0.2 to 2.0 meters as of 2100. Its low end, around 20 cm per century, is what you get simply by extrapolating long historical trends (as we did in, for example, our Sea Level Emergency Update for Bill Gates’ waterfront San Diego mansion.) The “Intermediate-Low” projection is for 0.5 m by 2100, which they said was based on previous IPCC model projections based on moderate emission paths. Then the “Intermediate-High” projection was 1.2 m by 2100, based on IPCC projections using high emission scenarios. And the Highest scenario was for 2.0 m of SLR based on worse-than-worst-case scenarios basically in which all the world’s major ice sheets disintegrate into the ocean at exceptional speed. And the authors coyly declined to assign probabilities to their set of scenarios, which not coincidentally allowed the usual media trick of highlighting the upper end in “up to 2 meters” hyperventilations.

In 2016 a new multi-agency report was prepared for the Department of Defence. It generated a range of projections falling in the same range (0.2 - 2.0 m by 2100) but this time they tweaked the various intermediate scenarios so that above 0.2 m they only fell on a 0.5 m-spaced grid: 0.5, 1.0, 1.5 and 2.0. Maybe the Navy only has rulers with 0.5 m markings. They also decided to trace their various scenarios back to what were then the newfangled IPCC RCP emission scenarios to indicate which ones would be consistent with which outcome. While 0.2 m and 0.5 m would be consistent with most of them, they found that anything at or above 1.0 m requires the RCP8.5 scenario. Which, as we have seen many times, is wildly, almost insolently implausible.

Then in 2017 a new multi-agency task force was formed and naturally things got worse. Instead of trimming the now-implausible high end, they moved the whole distribution even further up until it spanned 0.3 m to 2.5 m. The minor increase on the low end was based on an observed recent acceleration in satellite-derived SLR. Steve Koonin has previously pointed out that SLR also accelerated early in the 20th century then dropped back subsequently, so extrapolating from a short trend is potentially misleading, but even with that trick the rate is only 30 cm as of 2100. To get the 2.5 m high end required some crazy assumptions, which of course sailed through peer review in the multi-agency way of things. But when a new Task Force was assembled in 2022 they had the moderate good sense to drop the top end back to 2.0 m.

At this point, Weinkle shows, you need warming of about 5.0 C by 2100 to crank the SLR projections up just to 0.8 m, less than half of that figure. And if some even more extreme and highly unlikely scenarios concerning extreme ice loss events get thrown in, the SLR rate only goes up to 0.88 m. Yet the official projection range still has a 2.0 m top end. How do they justify it?

Weinkle goes through what passes for a justification and explains that, not surprisingly, there isn’t one. The low-likelihood high-impact contingencies are already used to get the 0.88 m figure. The 1.0 - 2.0 m projections are still there in the report but have no basis even in IPCC scenarios. As Weinkle notes:

“the US scenarios Intermediate High and High fall well outside the views of the IPCC. They are seemingly untethered from any logical justification.”

As you’d expect from an iterated series of interdepartmental committees.

Projections of 21st century sea level rise are not getting worse. The bureaucratic abuse of science, on the other hand, is.

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