Global Sea-level Rise: Faster than Ever?

sea levelIn yet another instance of the media jumping on the climate alarmist bandwagon, The New York Times this past February boldly headlined “Seas Are Rising at Fastest Rate in Last 28 centuries.” The article went on to proclaim “the worsening of tidal flooding in coastal communities is largely a consequence of greenhouse gases from human activity, and the problem will grow far worse in coming decades, scientists reported Monday.”

“Worsening tidal flooding”—”grow far worse”—scary words for coastal inhabitants, but do they help the reader understand what the two reports (here and here) actually said? More importantly, do they help the reader evaluate what was reported? Or does the NYT wording continue the intellectually shallow but emotionally potent sea-level terror theme of Al Gore’s movie, An Inconvenient Truth?

The two reports published in the Proceedings of the National Academy of Science (PNAS) made several claims. During pre-industrial history (prior to 1860), global sea level rose at an average rate of 0.1 to 0.3 mm/yr. From 1860 to 1900 it rose at an average rate of 0.4 mm/yr, and from 1900 to the present it has been rising at 1.4 mm/yr. The studies project for various hypothetical CO2 emission-increase scenarios during this 21st century a total rise in global sea level between 1 ft and 2.5 ft.

First, observe that “tidal flooding” is not the same as the spectacular “storm-surge” that accompanies severe coastal storms like Sandy or the fictionalized surge in the 2004 apocalyptic sci-fi film The Day After Tomorrow. Such surges can easily exceed the reports’ estimated increase in tidal flooding by ten times or more. You probably wouldn’t know that from media stories like the NYT piece. Mitigation of known storm surge damage could protect coastal communities from the worst guesses of sea-level rise for the rest of this century!

Second, forecasting sea-level rise involves even more guesswork than forecasting global warming. Actual sea-level direct measurement data exist only for a century and a half and only for a few regions of the earth. Even in the world’s best documented region, the eastern North Sea and Baltic region, tide-gage records of sea-level measurement are less than 200 years old. Estimates of sea-level changes over 28 centuries necessarily rely upon layers of interpretation of various proxies such as evidence of shoreline changes. Extensive modeling, therefore, is required as the two PNAS papers demonstrate. Each model element to some degree has to involve guesswork. Resulting estimates of sea-level rise rates vary from 1.15 mm/yr to about 3 mm/yr—a considerable variation for any long-term projections.

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