Global Mean Sea Level: Is It Accelerating? ... Or Is It Not?
Chambers, D.P, Merrifield, M.A. and Nerem, R.S. 2012. Is there a 60-year oscillation in global mean sea level? Geophysical Research Letters 39: 10.1029/2012GL052885.
Why is this finding so important?
First of all, the three researchers note that "an upturn in GMSL rise due to a 60-year oscillation with a minimum between 1980 and 1990 is consistent with the increased GMSL trend obtained from satellite altimetry (e.g., Nerem et al., 2010) and reconstructions since 1993." This fact, as they continue, "does not change the overall conclusion that sea level has been rising on average by 1.7 mm/year over the last 110 years." However, they rightly state that the 60-year oscillation does change "our interpretation of the trends when estimated over periods less than one-cycle of the oscillation." And, therefore, they conclude that "although several studies have suggested the recent change in trends of global (e.g., Merrifield et al., 2009) or regional (e.g., Sallenger et al., 2012) sea level rise reflects an acceleration, this must be re-examined in light of a possible 60-year oscillation [italics and bold added]," in further support of which contention they note that "there have been previous periods where the rate was decelerating, and rates along the Northeast U.S. coast have what appears to be a 60-year-period (Sallenger et al., 2012)," which they also indicate "is consistent with our observations of sea level variability at New York City and Baltimore."
As a final bit of advice in light of the results of their analysis, Chambers et al. prudently state that "one should be cautious about computations of acceleration in sea level records unless they are longer than two cycles of the oscillation," noting that this advice "applies to interpretation of acceleration in GMSL using only the 20-year record of satellite altimetry and to evaluations of short records of mean sea level from individual gauges."
Consequently, for those who buy into the storyline of these latter approaches, we can only say Buyer, Beware!
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