by Judith Curry
On the acceleration of sea level rise, the Gilligan effect, and the garbage solution.
From Chapter 3 of the AR5 SOD:
Two out of three reconstructions of GMSL (global mean sea level) from tide gauge data extending back to 1900 or earlier indicate non-zero acceleration. Estimates range from 0.000 to 0.013 [–0.002 to 0.019] mm yr–2, so it is likely that GMSL rise has accelerated since the early 1900s.
A fourth paper on this topic was recently published, that was not referenced in Chapter 3 of the SOD:
Twentieth century global mean sea level rise: is the whole greater than the sum of the parts?
J.M. Gregory et al.
Abstract. Confidence in projections of global-mean sea-level rise (GMSLR) depends on an ability to account for GMSLR during the 20th century. There are contributions from ocean thermal expansion, mass loss from glaciers and ice sheets, groundwater extraction and reservoir impoundment. We have made progress towards solving the “enigma” of 20th-century GMSLR—that is, the observed GMSLR has been found to exceed the sum of estimated contributions, especially for the earlier decades. We propose that: thermal expansion simulated by climate models may previously have been underestimated owing to their not including volcanic forcing in their control state; the rate of glacier mass loss was larger than previously estimated, and was not smaller in the first than in the second half of the century; the Greenland ice-sheet could have made a positive contribution throughout the century; groundwater depletion and reservoir impoundment, which are of opposite sign, may have been approximately equal in magnitude. We show that it is possible to reconstruct the timeseries of GMSLR from the quantified contributions, apart from a constant residual term which is small enough to be explained as a long-term contribution from the Antarctic ice-sheet. The reconstructions account for the approximate constancy of the rate of GMSLR during the 20th century, which shows small or no acceleration, despite the increasing anthropogenic forcing. Semi-empirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of our closure of the budget is that such a relationship is weak or absent during the 20th century.
The paper is an early online release for the Journal of Climate: abstract [here].
So . . . the addition of one more paper to the literature without an accelerating trend (2 out of 4) implies, according to the IPCC reasoning about uncertainty, that acceleration of sea level trend is ‘about as likely as not.’ Under this line of reasoning, the addition of one paper to the literature can change the assessment from ‘likely’ to ‘about as likely as not.’ And since the Gregory et al. paper seems to be superior from a methodological perspective, a more sophisticated assessment process would weight this paper more heavily. It looks to me like the IPCC needs to change this particular conclusion (especially the confidence level) in view of this new paper by Gregory et al.
My problems with the IPCC’s characterization of and reasoning about uncertainty are described in my paper Reasoning about climate uncertainty, and this particular case is a good example of the flimsiness of many of the confidence assessments, especially for data sets that have a low maturity level.
Here is something else of interest. While Chapter 3 is on the Oceans, Chapter 13 is on Sea Level Change. Chapter 3 did not mention the new Gregory et al paper, but Chapter 13 mentions the new Gregory et al. paper multiple times. In fact, Gregory is a lead author on Ch 13, and Gregory’s coauthor Church is coordinating lead author on Ch 13. The material in Ch 13 is on sea level acceleration is much better than that in Ch 3, but observed acceleration of sea level rise seems to belong to Ch 3. Hopefully, the authors of Ch 13 can motivate or provide a more sophisticated treatment of this issue in Ch 3, with a more defensible conclusion on this for the SPM.
The Gilligan effect
Willie Soon and Nils-Axel Morner have an article on this at the Washington Times, which is convincingly debunked by Tamino. The only reason I mention the WT article at all is for one of the comments, by Joe:
Long ago the TV series GILLIGAN’s ISLE dealt with the issue of sea level rise.
The Castaways (with no heat, no light, no motorcar, not a single luxury) were all in a panic as the measuring stick they used to measure the depth of their lagoon indicated that they would soon be underwater. (The Professor calculated it quite precisely).
Ultimately, they found out the Gilligan had been using the stick for something else, like catching lobsters, with a little bit getting broken off each time.
The skipper chased him around the beach, whacking him with his skipper’s hat, but otherwise the Castaways remained high and dry until their eventual rescue.
I think that pretty much explains the Global Warmists methodology as well.
JC message to the IPCC: the moral of the Gilligan story is that you can read too much into observational data sets that are not robust and have not reached a sufficient level of maturity.
The garbage solution
So, how might we be ‘rescued’ from sea level rise? A recent post by Andy Revkin suggests an interesting solution How a former landfill helped absorb hurricane’s surge. Excerpt:
During Hurricane Sandy, the Fresh Kills landfill on Staten Island absorbed a critical part of the storm surge. Its hills and waterways spared nearby neighborhoods like Travis, Bulls Head, New Springville and Arden Heights much worse flooding. The 2,200-acre site, which closed a decade ago and is being turned into a park, was also temporarily reopened as a transfer station, helping officials and relief agencies clear debris from around the city.
If many New Yorkers, Staten Islanders included, still can’t help thinking of the place as a mountain range of stinking trash, that’s understandable. But since its closing, Fresh Kills has become a model for landfill reclamation around the world, having been transformed into a vast green space full of wildlife. Now it is also demonstrating the role of wetland buffers in battling rising waters.
JC summary: The IPCC should ask the authors of Ch 13 to take a look at the sea level rise part of Ch 3, they seem to have a much better handle on the complexity of the issue. It looks to me that the evidence for accelerating anthropogenic sea level rise is pretty weak, and lost in the noise of natural variability (see also the previous sea level rise thread).
Given the low maturity of the GMSL data sets, it doesn’t make sense to use GMSL as a primary variable for documenting the existence of AGW. Rather, the practical issues associated with sea level rise are fundamentally local, and local sea level rise can be substantially different from GMSL rise. Practical solutions like land use policy and landfill seem to be a better choice than hoping to control sea level rise via reducing greenhouse emissions.