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Twentieth-Century Global Sea Level Rise
Holgate, S.J. 2007. On the decadal rates of sea level change during the twentieth century. Geophysical Research Letters 34: 10.1029/2006GL028492.

What was done
In a previous paper (Holgate and Woodworth, 2004), a mean global sea level history was derived from 177 coastal tide gauge records that spanned the period 1955-1998; and in an attempt to extend that record back in time another half-century, Holgate chose nine much longer high-quality records from around the world (New York, Key West, San Diego, Balboa, Honolulu, Cascais, Newlyn, Trieste and Auckland) to see if their combined mean progression over the 1955-1998 period was similar enough to the concomitant mean sea level history of the 177 stations to employ the mean nine-station record as a reasonable representation of mean global sea level history for the much longer period stretching from 1904 to 2003.

What was learned
In comparing the sea level histories derived from the two data sets, Holgate found that their mean rates-of-rise were indeed similar over the second half of the 20th century; and this observation thus implied, in Holgate's words, that "a few high quality records from around the world can be used to examine large spatial-scale decadal variability as well as many gauges from each region are able to [do]."

As a result of this finding, Holgate presented the nine-station-derived wavering black line in the figure below as a reasonable representation of the 1904-2003 mean global sea level history of the world, and based on that history calculated that the mean rate of global sea level rise was "larger in the early part of the last century (2.03 0.35 mm/yr 1904-1953), in comparison with the latter part (1.45 0.34 mm/yr 1954-2003)."

Another way of thinking about the century-long sea level history portrayed in the figure below is suggested by the blue curve we have fit to it, which indicates that mean global sea level may have been rising, in the mean, ever more slowly with the passage of time throughout the entire last hundred years, with a possible acceleration of that trend over the last few decades.

Cumulative increase in mean global sea level (1904-2003) derived from nine high-quality tide gauge records from around the world. Adapted from Holgate (2007).

What it means
Whichever way one looks at the findings of Holgate - either as two successive linear trends (representative of the mean rates-of-rise of the first and last halves of the 20th century) or one longer continuous curve - the nine select tide gauge records indicate that the mean rate of global sea level rise has not accelerated over the recent past, when climate alarmists have incessantly claimed that (1) the earth warmed to a degree that is unprecedented over many millennia, (2) the warming resulted in an accelerated melting of the vast majority of the world's mountain glaciers and polar ice caps, and (3) global sea level rose at an ever increasing rate. The real-world data-based results of Holgate clearly suggest that all of these claims are likely to be false.

Holgate, S.J. and Woodworth, P.L. 2004. Evidence for enhanced coastal sea level rise during the 1990s. Geophysical Research Letters 31: 10.1029/2004GL019626.

Reviewed 24 January 2007