By William D. Balgord
Reprinted with permission Richmond (VA) Times-Dispatch
The Union of Concerned Scientists, a not-for-profit advocacy group based in Cambridge, Mass., recently issued a report that drew immediate response from news outlets. UCS projects 17 U.S. military facilities, including Norfolk Naval Base, will have to deal with frequent flooding events from rising seas by the year 2050, and suggests the bases may be awash in 2100.
Dire predictions are based on model projections suggesting a future atmospheric temperature rise of 2 degrees or more accompanied by partial melting of the massive glaciers that cover Greenland and Antarctica. But climate models, not yet validated, deserve criticism because of poor correlation between increasing CO2 and a global temperature that has not risen in close conformity with model predictions. Absent global temperature increases, significant melting of either polar icecap would not occur.
Warming oceans contribute to rising sea level, since volume expands as upper ocean layers warm. For several thousand years sea levels have risen at a rate of about 7 inches per century, with a dip during the Little Ice Age. Reports of accelerating sea level rise (SLR) may be attributed to a switch in instrumentation (tidal gauges to satellite measurements).
Shifting weather patterns and changes in ocean-atmospheric circulation such the El Nino/La Nina events in the equatorial Pacific are also responsible for short-lived changes. A five-inch rise projected from historic trends would be entirely manageable for the DOD. The Dutch have battled a rising North Sea for centuries.
UCS’ report does not properly refer to on-shore tide gauge measurements as Relative Sea Level (RSL). RSL reflects average sea level of the nearby open ocean as measured at the shoreline referenced to a permanent stationary structure usually located in a harbor.
Relative Sea Level Rise (RSLR) is phenomenon whereby sea level appears to rise if either or both the ocean rises or the land settles. The latter is called “subsidence.” To determine what contributes to observed changes requires detailed analysis of coastal features aided with satellite altimetry. RSLR determines the increased risk of flooding during spring tides and more dramatically from tidal surges accompanying hurricanes or tsunami.
Norfolk Naval Base is located near the mouth of Chesapeake Bay, an embayment encompassing the drowned river valleys of the James, Potomac, and Susquehanna Rivers (and tributaries). It is a prime example of land undergoing subsidence accompanying the relaxation of the forced downward tilt of the North American tectonic plate now returning to its position before the previous glacial age.
Subsidence along the bay’s perimeter is proceeding at a rate of half an inch to as much as two inches per decade. Research at the Virginia Institute of Marine Science also concluded somewhat more than half the RSLR observed from 1976 to 2007 resulted from subsidence.
Increasing sea levels projected by UCS depend on an appreciably accelerated melting of polar ice and thermal expansion of the oceans, not yet observed in the 21st Century.
Consistent departures of actual temperatures from EPA model projections raise further questions and relegate predictions of future ice melt and ocean expansion to the status of speculation.
Many experts had predicted sea ice in the Arctic Ocean would melt completely by 2008. Yet the ice remains in late summer. Although fluctuating somewhat year to year, it does not show indications of disappearing. The Arctic Ocean refreezes each winter.
Sea ice surrounding Antarctica has been expanding for nearly two decades despite earlier predictions to the contrary. It is generally agreed that for melting of landed ice to proceed, contributing to SLR, Arctic sea ice and that ringing Antarctica would need to disappear.
The extent of sea ice, although not affecting sea level directly, is considered a bellwether for potential melting of the icecaps.
Perceived threats posed by rising oceans to U.S. bases in 2050 hinge on climate models that have not been validated. The threats remain speculative. And with CO2 sensitivity revised down one degree Celsius for a doubling of CO2, there is reasonable doubt that warming this century would induce sufficient melting or enough thermal expansion to fulfill USC’ predictions.
Yet subsidence causes problems wherever coastal lands are sinking, whether in Norfolk, New Orleans or Venice, and will proceed independently of any global warming alleged from the combustion of fossil fuels.
The Department of Defense is advised to plan accordingly.