Holgate reported in his poster that sea level rose more in the first half of the 20th century – an observation which is not mentioned in AR4 as far as I know.
When the decadal rates of change are integrated over the entire twentieth century we obtain the figure on the right. Sea level can be seen to have risen around 170 mm on average over the past century. The mean rate for the twentieth century calculated in this way is 1.67⯰.04 mm/yr. The first half of the century (1904-1953) had a slightly higher rate (1.91⯰.14 mm/yr) in comparison with the second half of the century (1.42⯰.14 mm/yr 1954-2003).
There is a slight difference in the last part of the image between the poster and the GRL article, which was observed by John Bell. The GRL version has an uptick at the end that is not present in the poster, which, as noted below, is a result of the incorporation of additional information in the final article, which is the final version.
Now here’s a figure that intrigued me – a graph showing the rate of change. The version below is the GRL version – the poster version is a little different.
Holgate 2007 Figure 2. Comparison of the global mean decadal rates of sea level change based on the nine records with the rates from the 177 stations used in HW04. All rates are corrected for glacial isostatic adjustment and inverse barometer effects. The shaded region indicates ⯱ standard error.
Doesn’t it look like there’s something like an 11-year cycle in this? Remind you of anything? I know that it’s a bit of a mug’s game trying to identify solar cycles, but here’s a plot of sun spot numbers in the same period. The maxima and minima of the solar cycles seem to match the fluctuations in sea level rise rather uncannily. While the resemblance is impressionistic (I don’t have a digital version of Holgate’s series), offhand, I can’t think of any two climate series with better decadal matching. I think that this resemblance is pretty obvious. Notwithstanding this obvious resemblance that surely deserves some commentary, Holgate does not even mention the word “solar”, but does mention volcanic forcing.
Update: In response to an inquiry from a CA reader, Holgate gave the following response on solar/sea level connections:
Many people have tried to link climate variations to sunspot cycles. My own feeling is that they both happen to exhibit variability on the same timescales without being causal. No one has yet shown a mechanism you understand. There is also no trend in the sunspot cycle so that can’t explain the overall rise in sea levels even if it could explain the variability. If someone can come up with a mechanism then I’d be open to that possibility but at present it doesn’t look likely to me.
If you’re interested in solar cycles and sea level, you might look at a paper written by my boss a few years back: Woodworth, P.L. “A world-wide search for the 11-yr solar cycle in mean sea-level records.” Geophysical Journal of the Royal Astronomical Society. 80(3) pp743-755
You’ll appreciate that this is a well-trodden path. My own feeling is that it’s not the determining factor in sea level rise, or even accounts for the trend, but there may be something in the variability. I’m just surprised that if there is, it hasn’t been clearly shown yet.
S. J. Holgate, On the decadal rates of sea level change during the twentieth century, url