Global Sea-level Rise: Faster than Ever?

by Charles Clough

In 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 21^st 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.

Third, tide gages and proxies give relative sea-level, not absolute sea-level. They show sea-level relative to the land level. Absolute sea-level measurements from satellite only began in the early 90s—too recent to establish significant trends. To obtain absolute sea-level measurements from relative measurements or proxies, scientists have to correct for many variables—vertical changes in both land and ocean basin levels, ocean salinity changes, overland glacial decreases and increases, on-shore-off-shore prolonged winds, and gravitational interactions between the earth and lunar orbits. Would readers of media headline articles know that?

Finally, there is the problem of learning how long the oceans take to reach equilibrium once there is a change in global temperature. Temperatures have been generally rising and sea-levels with them ever since the end of the ice age thousands of years ago. But there have been numerous up-and-down oscillations in this general trend, none of which is well understood. Are we in one or more of these oscillations now?

Given these caveats in the reasoning behind the claim that “seas are rising at the fastest rate in the last 28 centuries,” it comes as no surprise that renowned experts in the field like Dr. Nils-Axel Mörner of Sweden don’t take these reports seriously. Mörner challenges one of the PNAS papers, pointing out several of its conflicts with actual observations: nowhere do global tide gauges show valid increases in the rate of sea-level rise, and new satellite altimetry of absolute sea-level when carefully calibrated shows a mean rise of 0.5 mm/yr, not the modeled 1.4 mm/yr.

Since atmospheric CO₂ emission levels do not correlate with such changes prior to the industrial age, the upward trend in temperature and sea level will continue regardless of the political campaign to impose economy-destroying carbon asceticism on the world’s population. Readers of such articles ought to heed the advice of Harvard oceanographer Roger Revelle (whom Al Gore claimed taught him fear of global warming’s planetary effects). Revelle’s last published article (co-authored with S. Fred Singer and Chauncey Starr) before his death was entitled “What to Do about Global Warming: Look before You Leap” (Cosmos 1 (1991): 28–33).

Atmospheric physicist Charles Clough, Bel Air, MD, is retired chief of the U.S. Army Atmospheric Effects Team at the Aberdeen Proving Ground, MD; retired Lt. Col., U.S. Air Force Reserve Weather Officer; President of Biblical Framework Ministries; adjunct Professor at Chafer Theological Seminary, Albuquerque, NM; and a Fellow of the Cornwall Alliance for the Stewardship of Creation.