Tuesday, 17 April 2012

Making it up (2) - "Sea level 'rising fastest in SW Pacific"

Here we go again! A tranch of syndicated articles, or variation on same, which take a straightforward analysis of proxy data (which is from the past, by definition), and transpose its findings to the present or even the future. The cited paper is "Nineteenth and twentieth century sea-level changes in Tasmania and New Zealand", Gehrels et. al., though of course it takes either a site search, or a Google search to actually find an abstract, as it's just vaguely referenced, or the journal main page is given. As I've said before, this gives the distinct impression that the article authors would prefer we accept their take on it, without the benefit of reading the paper and making up our own minds. In this case, that would instantly debunk their alarmist conclusions, and in several cases, reveal that the authors either can't read and comprehend, or can but distort or even make up conclusions, effectively putting words into the mouths of the paper's authors. The abstract says
Positive deviations from linear sea-level trends represent important climate signals if they are persistent and geographically widespread. This paper documents rapid sea-level rise reconstructed from sedimentary records obtained from salt marshes in the Southwest Pacific region (Tasmania and New Zealand). A new late Holocene relative sea-level record from eastern Tasmania was dated by AMS14C (conventional, high precision and bomb-spike), 137Cs, 210Pb, stable Pb isotopic ratios, trace metals, pollen and charcoal analyses. Palaeosea-level positions were determined by foraminiferal analyses. Relative sea level in Tasmania was within half a metre of present sea level for much of the last 6000 yr. Between 1900 and 1950 relative sea level rose at an average rate of 4.2 ± 0.1 mm/yr. During the latter half of the 20th century the reconstructed rate of relative sea-level rise was 0.7 ± 0.6 mm/yr. Our study is consistent with a similar pattern of relative sea-level change recently reconstructed for southern New Zealand. The change in the rate of sea-level rise in the SW Pacific during the early 20th century was larger than in the North Atlantic and could suggest that northern hemisphere land-based ice was the most significant melt source for global sea-level rise.
That seems straightforward - sea level at the sample site rose at a relatively high rate (compared with the global rate) between 1900 and 1950, and a relatively low rate for the rest of the 20th century. Nothing to worry about then? Not according to several reports from "down under", whose almost identical articles, begin News.com.au (Australia):
SOUTHERN Australia and nearby Pacific nations are likely to be the most seriously affected in the world by the continuing rise in sea levels, according to new research.
... and 3 news (new Zealand
The seas around New Zealand and Australia are likely to be the most seriously affected in the world by the continuing rise in sea levels, according to research on Tasmanian swamps.
"According to research"? Apparently not, the paper abstract doesn't mention the future - remember that the paper's titled "Nineteenth and twentieth century sea-level changes in Tasmania and New Zealand". However, all the articles I've seen quote one of the authors, Patrick Moss:
"Sea levels in Tasmania remained relatively stable for much of the past 6000 years, but around 1880 they started rising drastically," said Dr Moss, who co-wrote the study in conjunction with scientists from the UK, New Zealand and Australia. 
From several reports:
Sea levels in the southwest Pacific rose at four times the average 20th-century rate between 1900 and 1950, according to the study.That was followed by a period of “relative quiet” broken by a second spike in 1990 which saw sea levels rise at a rate that defied projections.”The natural climatic factors seem to be not as apparent and anthropogenic climate change seems to be the key possible culprit,” said Moss.
Dr Moss said a jump in sea levels occurred after 1990.
"The rise in 1910 probably reflects the end of the little ice age, when temperatures were about one to two degrees cooler in the northern hemisphere than today," he said.
"The 1990s peak is most likely indicative of human-induced climate change."
Sounds rather like someone with an agenda - that conclusion's not in the paper. Why does he call it a "peak"? Because that's what it is, and both his sediment proxies and tide gauges in the SW Pacific generally show a decline since. The diagrams in the paper clearly show that. You have to follow the pea as the cups are moved, and analyse every word, or you might, as these web authors clearly have, assume the "jump" is still in progress. Elsewhere he says "A large ice-melt is like a fingerprint". There's that word again - if there's been a decline since the 1990s, then the "fingerprint" is rather blurred, and the "points of identity" are insufficient to identify the culprit. More to the point, what exactly was the "fingerprint" of the early 20th century rise? Here's yet another researcher putting his mouth where his paper isn't, and confirming our suspicions of his prejudice and unjustified conclusions.

What about that "lack of comprehension" I mentioned at the beginning? here's a good example from "Adelaide Now" - first the bogus prediction based on no evidence from the paper, nor its self-appointed spokesman (not the lead author), Moss
SOUTHERN Australia and nearby Pacific nations are likely to be the most seriously affected in the world by the continuing rise in sea levels, according to new research.
Then the silly error, repeated in several reports, including Planetsave (save it for whom and from what?)
Sea levels have risen approximately 20 centimetres in the South West Pacific Ocean since the end of the 19th century, a dramatic increase according to a new study released this week.

Scientists found that sea levels in Tasmania remained relatively stable for most of the previous 6,000 years but that around 1880 they started to rise dramatically. Between 1900 and 1950 the sea level rose at an average rate of 4.2 millimetres per year. The highest rates of sea level rise occurred in the 1910s with an increase of .3 to .8 millimetres per year, followed by a second peak in the 1990s.
If sea level rose 20cm since the late 19th century, and if the rate of rise between 1900 and 1950 was 4.2mm a year, which amounts to 4.2 x 50 = 210mm or 21cm, can we deduce it's fallen by 1cm since 1950?

I might add that I can see nothing like a rise of 4.2mm since 1900 for tide-gauges in the southern part of Australia, nor any "spike" in the 1910s. Perhaps I'll update this post with a few charts to illustrate that.

No comments:

Post a Comment