From Climate Realism

By Linnea Lueken

The Financial Times (FT) recently posted an article titled “Sea levels already ‘much higher’ than many scientists had estimated,” claiming that sea level rise is even more concerning than previously believed because modelled sea level estimates used in many climate change studies are generally lower than actual sea level measurements. The importance of the finding, however, is not what the story reports. The story notes that present sea levels are not catastrophic. Also, the present rate of sea level rise, whether based on satellite calculations or as measured by tide gauges, is very gradual. Seaside communities have the ability to overcome any threat from rising seas through normal civil engineering efforts.

FT reports on a recent study from The Netherlands’ Wageningen University, published in Nature. According to the authors of the study, most coastal planning including planning for flooding and sea level rise is based on “Geoid” model estimates of coastal sea-level height and land elevation. Yet, like general circulation models, the outputs of these models are only as good as the data and assumptions built into them. In this case, the authors of the study found that that “actual sea levels are on average about 30cm higher globally than estimates produced by the usual scientific models,” with differences emerging particularly in Southeast Asia and Oceania. FT says that in those regions, “the ocean is one to 1.5 meters higher on some coastlines than most impact assessments have assumed.”

This is notable because it means that many climate impact assessments for coastal communities have been designed from the wrong starting point, projecting future sea levels and problems from them, in many instances at levels that already are the case. The problems they anticipate under future climate change driven sea levels should already be evidenced, but they aren’t. Garbage in, Garbage out.

Because those coastal communities seriously miscalculated the sea level starting point, the study project’s leader, Philip Minderhoud, warned that this could mean the “the impacts from sea-level rise will happen sooner than projected before.” Yet, that seems wrong, since sea levels are already at where the coastal planning estimates they will be decades in the future. If these problems don’t exist now, the planning is wrong from the start about possible impacts. The study does not show that seas are rising faster than they have historically. Thus, planning should begin from where coastlines actually are.

That means, take them in relation to current sea levels, with future estimates based on rates of rise under recent climate change – not, as is done with this study, based on IPCC estimates tied to unrealistic emissions scenarios.

Climate Realism has long pointed out (here, here, and here, for example) that factors such as land subsidence are reflected in measurements of sea level rise, which makes it difficult to gauge how much local sea level rise has occurred and will occur in the future.

The FT sought comments from Anders Levermann, of the Potsdam Institute for Climate Impact Research, concerning the implications of the study, who forecast, “eventually” we will see a sea level rise of “three to four meters,” though he admits average sea level has only risen about 20cm, or about 7 inches, over the past century. “Eventually” could be technically right, though in this case eventually would mean 1,000 to 2,000 years from now. That’s not an immediate catastrophe and a time interval over which no model, set of models, or estimates by so-called experts should be trusted or used to shape policies affecting people today and for the next several centuries.

In fact, there is significant scientific doubt that sea level rise is accelerating at all. Another recent Dutch study, published in the Journal of Marine Science and Engineering, examined sea level measurements from more than 200 tide gauge stations worldwide. They found that the average global rate of sea level rise has been about 15 centimeters per century. This, and the 20 cm rate estimated in the Nature study, are both lower rates than experienced over much of the past 15,000 years. At either of these rates, coastal communities have centuries to adapt to rising seas or mitigate them by hardening infrastructure, or even by moving communities inland, if that is deemed necessary.

The authors of the Journal of Marine Science and Engineering study acknowledge that sea level rise projections by groups like the Intergovernmental Panel on Climate Change are biased upwards by 2mm per year compared to accurate measurements as recorded by tide gauges.

Similarly, other recent studies looking at the contributions of Antarctic ice melt, and ice sheet models in general, have found that many climate scientists rely too heavily on models rather than data. As a result, they are likely overstating how much sea level rise could be added in the future by melting ice at the north and south poles, or even if ice sheet decline will consistently continue in the future.

The new study reported on by FT is interesting, but it is certainly not alarming. If sea levels along the world’s coastlines are consistently at or near the heights coastal community planners estimated in the future would mean disaster, then it is good news. That’s because those communities aren’t experiencing the disasters the planners were concerned about. As a result, it does not follow that people should be even more concerned now about future rise, especially sea levels 1,000 to 2,000 years in the future, by which time the climate could have shifted again and the Earth headed back to a new glacial cycle. We just don’t know.

Available data show there is no acceleration in recent rates of sea level rise as measured by tide gauges, as opposed to the rates of rise calculated by satellites. Fifteen or even 20 centimeters per century is not the end of the world. Coastal cities have handled much steeper rates of rise in the past. There is no reason to think, with the time involved and the pace of technological change, coastal cities can’t adapt to similar changes in the future.