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Global Sea Level: What is it doing? And why?
Reference
Kolker, A.S. and Hameed, S. 2007. Meteorologically driven trends in sea level rise. Geophysical Research Letters 34: 10.1029/2007GL031814.

Background
The authors note that determining the rate of global sea level rise (GSLR) is complicated by non-tidal, short-term and local variability that is "orders of magnitude greater than the trend." So complex is the issue, in fact, that the recent rate of GSLR has been estimated to be about 1.1 mm/year by Wadhams and Munk (2004), 1.5-2.0 mm/year by Miller and Douglas (2004), and 3.1 ± 0.7 mm/year by the IPCC (2007), a spread that is much larger than what everyone would like to see.

What was done
Whereas most previous attempts to calculate rates of GSLR "coped with the problem of interannual and decadal scale variability by averaging large or long-term data sets," in the words of Kolker and Hameed, "an alternative approach is to determine the cause of this variability." Noting that GSLR variability has been linked to storms, winds, floods, Rossby waves, shifts in major ocean currents, volcanically-induced ocean heat content variations, and the El Niño Southern Oscillation -- with further regional complications introduced by subsidence, uplift, tectonics, freshwater fluxes and thermosteric effects -- they attempt to resolve this knotty problem by showing that "a major fraction of the variability and the trend in mean sea level at key sites along the Atlantic Ocean are driven by shifts in the position and intensity of the major atmospheric pressure centers that reside over the Atlantic Ocean, the Azores High and the Icelandic Low," which they refer to as atmospheric centers of action (COAs).

What was learned
When all was said and done, the two researchers found that "a large fraction of the annual mean sea-level variability at the five Atlantic Ocean stations is correlated with shifts in the position and intensity of the COAs," which suggests that "meteorological processes drive coastal sea-level variability by redistributing water, heat, and the response of the ocean to atmospheric pressure across the ocean basin." Utilizing this knowledge, and depending on what assumptions they employed at various stages of their analyses, they obtained four sets of 20th-century mean rates of sea-level rise for the entire North Atlantic Ocean: 0.49 ± 0.25 mm/year, 0.59 ± 0.14 mm/year, 0.72 ± 0.33 mm/year and 0.93 ± 0.39 mm/year.

What it means
Noting that their results "yield rates of recent sea level rise that are closer to Wadhams and Munk's 1.1 mm/year than Miller and Douglas's 1.5-2.0 mm/year," Kolker and Hameed suggest that their findings could close what they call "the enigmatic gap in GSLR rates" if their results are characteristic of other major ocean basins, which they probably are, as they note that "atmospheric centers of action exist in all ocean basins." If such eventually proves to be the case, the lower GSLR rates derived by them and Wadhams and Munk would be much less than the 3.1 ± 0.7 mm/year GSLR rate of the IPCC (2007), which would in turn cast great doubt upon the huge magnitude of CO2-induced global sea level rise that is typically predicted by the world's climate alarmists.

References
Intergovernmental Panel of Climate Change (IPCC). 2007. Climate Change 2007: The Physical Science Basis. Contributions of Working Group 1 to the Fourth Assessment Report of the Intergovernmental Panel of Climate Change. Cambridge University Press, New York, NY, USA.

Miller, L. and Douglas, B.C. 2004. Mass and volume contributions to twentieth-century global sea level rise. Nature 428: 406-409.

Wadhams, P. and Munk, W. 2004. Ocean freshening, sea level rising, sea ice melting. Geophysical Research Letters 31: 10.1029/2004GL020039.

Reviewed 16 January 2008