Sea Level Rise: Up, Up and Away!

Sea levels, after several thousand years of little or no change, began to rise steadily in the early 1900s, trailing the Industrial Revolution and the increased use of fossil fuels by decades.  Projections for future rise vary from difficult to catastrophic.  A report released on Friday, June 22, 2010 by the National Research Council, the research arm of the National Academy of Sciences, has occasioned  a spate of articles, with only a few making it to the front pages.  SF Chronicle: David Perlman; Newser;  AFP;  NY Times (using AP)

The West Coast papers emphasize the difference in expected sea level rise in the California of the San Andreas fault, and the California north of Cape Mendocino, Oregon and Washington which rides up over the subsiding Juan de Fuca ocean plate.

For the California coast south of Cape Mendocino, the committee projects that sea level will rise 4–30 cm [1.6″-11.8″] by 2030 relative to 2000, 12–61 cm [4.7″- 24″] by 2050, and 42–167 cm [16.5″ – 65.7″] by 2100. For the Washington, Oregon, and California coasts north of Cape Mendocino, sea level is projected to change between -4 cm (sea-level fall) and +23 cm by 2030, -3 cm and +48 cm by 2050, and 10–143 cm by 2100.

 On the East Coast attention is focused on a 600 mile “hot spot“ from Cape Hatteras to Boston where a second report, from the U.S. Geological Service, says the sea is rising 3-4 times faster than the global average.

In absolute figures, sea levels on this stretch of coast have climbed by between 2 and 3.7 millimetres per year since 1980, whereas the global increase over the same period was 0.6–1.0 millimetres per year.

The existence of the hotspot is consistent with the measured slowing of Atlantic Ocean circulation, which may be tied to changes in water temperature, salinity and density in the subpolar north of the ocean.

The researchers predicted that by 2100, sea levels in the hotspot would rise by between 20 and 29 centimetres above the global increase, which most oceanographers predict will be about one metre.

The meat of the NRC report is here:

Sea-level change is one of the most visible consequences of changes in the Earth’s climate.
A warming climate causes global sea level to rise principally by (1) warming the oceans, which
causes sea water to expand, increasing ocean volume, and (2) melting land ice, which transfers
water to the ocean. Tide gage and satellite observations show that global sea level has risen an
average of about 1.7 mm yr over the 20th century (Bindoff et al., 2007), which is a significant
increase over rates of sea-level rise during the past few millennia (Shennan and Horton, 2002;
Gehrels et al., 2004). Projections suggest that sea level will continue to rise in the future (Figure
1.1). However, the rate at which sea level is changing varies from place to place and with time.
Along the west coast of the United States, sea level is influenced by changes in global mean sea
level as well as by regional changes in ocean circulation and climate patterns such as El Niño;
gravitational and deformational effects of ice age and modern ice mass changes; and uplift or
subsidence along the coast. The relative importance of these factors in any given area determines
whether the local sea level will rise or fall and how fast it will change.

FIGURE 1.1 Estimated, observed, and projected global sea-level rise from 1800 to 2100. The pre-1900 record is based on geological evidence, and the observed record is from tide gages (red line) and satellite altimetry (blue line). Example projections of sea-level rise to 2100 are from IPCC (2007) global climate models (pink shaded area) and semi-empirical methods (gray shaded area; Rahmstorf, 2007). SOURCES: Adapted from Shum et al. (2008), Willis et al. (2010), and Shum and Kuo (2011)

The report was requested by ten state and federal agencies including 4 in California (see ix of the report) which want the best information for planning purposes — unlike the North Carolina Senate which recently passed a bill regulating which measurements were to be used in calculating sea-rise.  [It appears that the scorn storm breached the walls of idiocy and the bill has now been re-written, having been resoundingly rejected by the NC House.]

Here’s a handy little map device to drill down to your back yard and see how sea level rise might affect you (This is a linear plot, so it doesn’t take in the variances reported on above.  Interesting nevertheless.]