An odd kind of Icon

BPSDBThis one has been going around for a while now, so it isn’t new.
Apologies if you’re already aware of it, but if you haven’t come across it before, read on.

A reader recently pointed us towards a poster at http://meteo.lcd.lu/globalwarming/Holgate/sealevel_change_poster_holgate.pdf as evidence that rising sea levels are no threat to humanity. In his view the key sentence appears to be

The first half of the century (1904-1953) had a slightly higher rate (1.91±0.14 mm/yr) in comparison with the second half of the century (1.42±0.14 mm/yr 1954-2003).

Conclusive proof, apparently, that the residents of Tuvalu and Bangladesh have nothing to fear and that sea level rise is the greatest lie ever told.

As I said it’s been doing the rounds for a while now. It was picked up (among others) by climateaudit, jennifermarohasy and wattsupwiththat. Amusingly, all three had a go at twisting it into “It’s the Sun!” by assuming correlation equals causation.

The link points to a pdf document boasting logos from both the Proudman Oceanographic Laboratory (POL) and the Natural Environment Research Council (NERC), so at first glance it seems to be genuine.
The odd thing is the url: it doesn’t point to either POL or the NERC, as you might expect. Instead, it points to a (horribly garish) denialist wesite in Luxembourg, with links to WUWT & Climateaudit and quotes from Lindzen and Crichton on the home page.

I’ve tried searching for “the poster” on both the POL and the NERC websites without success. That doesn’t man that it didn’t originate from POL, it just means that I can’t find it.

Leaving that aside, what does the poster actually tell us?

Actually not a lot, apart from the quote above. Although it doesn’t cite it, the poster mostly consists of snippets from “On the decadal rates of sea level change during the twentieth century” (S. J. Holgate, GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L01602).
There are some small differences between the paper and the poster (and a typo in the poster that isn’t in the paper), so it’s possible that the poster predates the paper.

The paper itself is rather interesting. Holgate explores the idea that you can examine decadal changes in sea level by using a small number of high quality records. He finds that

the two highest decadal rates of change were recorded in the decades centred on 1980 (5.31 mm/yr) and 1939 (4.68 mm/yr) with the most negative decadal rates of change over the past 100 years during the decades centred on 1964 (−1.49 mm/yr) and 1987 (−1.33 mm/yr).

He finds a global increase of 174 mm over the 100 year period, and does indeed state that the rate in the first half of the 100 year period was greater than that in the second, but notes that “the difference in rates was not found to be significant”.

So does this paper dramatically contradict the IPCC and bring the whole climate change conspiracy edifice crashing down around us?

No.

Neither of the IPCC’s TAR and AR4 reports claimed that there was any significant acceleration in the rate of sea level rise during the 20th century. The TAR suggested a central value of 1.5 mm/yr for the century, whilst the AR4 suggests 0.17 metres for the century. Both mention that there are strong regional and temporal fluctuations in sea level.

Holgate’s paper is entirely consistent with the IPCC view – and in fact the AR4 cites a 2004 paper that Holgate co-authored.

There are a growing number of scientists who think that the IPCC estimates for sea level rise during the 21st Centrury are too low. Perhaps Holgate disagrees with them?

Again, it would appear not.

Holgate and Stefan Rahmstorf (of RealClimate fame) did have a bit of a dispute in Science, but this was about analysis techniques. Such discussions are normal and natural, and part of the way that science evolves.

But, as Martha notes, Holgate does not dispute that the threat is real. As quoted by the BBC:

However, a rise of even a metre could have major implications for low-lying countries – especially, noted Dr Holgate, those whose economies are not geared up to build sophisticated sea defence systems.

“Eighty to 90% of Bangladesh is within a metre or so of sea level,” he said, “so if you live in the Ganges delta you’re in a lot of trouble; and that’s an awful lot of people.”

IMAGE CREDITS:

All images are from The Proudman Oceanographic Laboratory.

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