Is There A 60-year Oscillation In Global Mean Sea Level?

  • Date: 05/11/12

A new paper published last month in GRL by Chambers, Merrifield and Nerem, entitled “Is there a 60-year oscillation in global mean sea level?” questions whether there has in fact been any underlying acceleration in the rate of rise.

http://sealevel.colorado.edu/content/2012rel4-global-mean-sea-level-time-series-seasonal-signals-retained 

We are often told that the rate of sea level rise has been accelerating since satellite monitoring began in 1992. We already know that 1992 is not a very representative place to start from, as Church & White tell us :-

However, the reconstruction indicates there was little net change in sea level from 1990 to 1993, most likely as a result of the volcanic eruption of Mount Pinatubo in 1991.”

The University of Colorado claim that the rate of sea level rise since 1992 is 3.1mm/year, but this includes an isostatic adjustment of 0.3mm/year, meaning that the sea level, as measured on our coastline, is only rising by 2.8mm/year. (Basically, they argue the sea floor is sinking: more information here). Taking this  along with the Pinatubo factor, it is clear that the underlying rate of rise is not much greater than the generally accepted 20thC rise of about 190mm.

But a paper published last month in GRL by Chambers, Merrifield and Nerem, entitled “Is there a 60-year oscillation in global mean sea level?” questions whether there has in fact been any underlying acceleration in the rate of rise at all.

ABSTRACT

We examine long tide gauge records in every ocean basin to examine whether a quasi 60-year oscillation observed in global mean sea level (GMSL) reconstructions reflects a true global oscillation, or an artifact associated with a small number of gauges. We find that there is a significant oscillation with a period around 60-years in the majority of the tide gauges examined during the 20th Century, and that it appears in every ocean basin. Averaging of tide gauges over regions shows that the phase and amplitude of the fluctuations are similar in the North Atlantic, western North Pacific, and Indian Oceans, while the signal is shifted by 10 years in the western South Pacific. The only sampled region with no apparent 60-year fluctuation is the Central/Eastern North Pacific. The phase of the 60-year oscillation found in the tide gauge records is such that sea level in the North Atlantic, western North Pacific, Indian Ocean, and western South Pacific has been increasing since 1985-1990. Although the tide gauge data are still too limited, both in time and space, to determine conclusively that there is a 60-year oscillation in GMSL, the possibility should be considered when attempting to interpret the acceleration in the rate of global and regional mean sea level rise.

http://sealevel.colorado.edu/content/there-60-year-oscillation-global-mean-sea-level

Of course, none of this should come as any real surprise. Leading expert, Bruce Douglas, warned us that “It is well established that sea level trends obtained from tide gauge records shorter than about 50-60 years are corrupted by interdecadal sea level variation”. It is also clear from his graph, below, that there have been periods during the 20thC when sea level has been increasing faster than at other times, notably in the 1970’s which were followed by a sea level falls in the 1980’s.

http://230nsc1.phy-astr.gsu.edu/hbase/thermo/searise.html

Will we hear about any of this from the team? Silly question really.

Not A Lot Of People Know That, 5 November 2012