A natural phenomenon that scientists find extremely difficult to measure, rising sea levels are nevertheless often summoned as evidence that environmental disaster looms if industrialized nations do nothing to curtail their emissions of climate-warming greenhouse gases.
In a late 1998 report for the National Center for Policy Analysis, Gerald T. Westbrook of Houston-based TSBV Consultants sheds light on the science of sea levels and global warming.
Sea levels rise naturally during interglacial periods (the periods between ice ages), notes Westbrook, and since the end of the last Ice Age 20,000 years ago, levels have risen 400 feet, at an annual rate ranging from 1/16 to 1/8 inch. Over the past 7,500 years, the annual increase in sea levels has remained at 1/16 inch.
According to a recent report issued by the Intergovernmental Panel on Climate Change (IPCC), the median observed sea level rise during the past century was 7 inches; Westbrook notes that scientists’ measurements of sea level rise during that period range from 4 inches to 10 inches.
“This six-inch range of observed sea level rise is almost as great as the median rise of seven inches, which demonstrates the difficulty of measuring sea level rises,” Westbrook notes. “Since it is so difficult to measure past rates of rise, it will surely be far more difficult to predict future rates.”
The IPCC report also addressed the cause of the century’s observed sea level rise, asking whether it could be attributed to the average global temperature increase of 0.5 to 1.1 degrees Fahrenheit that occurred over that period. After examining five possible sources of sea level rise–thermal expansion of water as temperature rises, melting of inland glaciers, melting of Greenland’s ice sheet, melting of Antarctica’s ice sheets, and changes in surface and ground water levels–the IPPC concluded there was insufficient data to “demonstrate a temperature effect on sea level rise for the past 100 years.”
Westbrook cites the downward revision of temperature and sea level rise forecasts made in the early 1980s as further proof that such predictions are anything but the “settled science” that politicians claim them to be.
Despite the many scientific uncertainties and scaled-back forecasts, dark predictions for the future continue to be issued, unabated. The Environmental Defense Fund and Smithsonian Institution, for example, cosponsored a traveling “educational” exhibit that depicted the Washington Monument slowly disappearing under water by the year 2075. Westbrook contends that more research is needed before the U.S. and other countries embark on any worldwide effort to address with sea level activity. “Until human-caused warming can be distinguished from natural climate variability,” he warns, “we risk wasting vast amounts of resources by signing global warming treaties prematurely.”
Westbrook acknowledges that, in some areas of the world, sea levels may rise by 1 to 2 feet during the next century. There are, he offers, more practical ways to address such sea level “hot spots.”
“This could mean no additional efforts in some areas and possibly building or strengthening sea walls or dikes in other areas,” for example. “It could also mean developing strong disincentives for living along the coast and even to relocating very vulnerable populations,” such as those in Papua, New Guinea, who were devastated by a recent tsunami.