[Coral-List] Atolls and SL rise

[Richard Dunne]

  Dear Paul and List

By casting aside the more recent evidence from Han et al 2010 (Nature 
Geoscience) into the category of "a little absurd" you fail to 
distinguish between regional sea-level rise and globally averaged 
effects, between analysis which incorporate regional ocean-atmosphere 
circulation changes and which do not, between examination of recent 
(from the 1960s up to 2008) rates of change, and those incorporating 
semi-empirical modelled and predicted events. These things cannot be 
easily resolved or selectively dismissed in this way.

Han et al. conclude "Our results indicate that warming-induced regional 
atmospheric circulation changes - although challenging for climate 
models, especially over the Indian monsoon region - should be considered 
seriously, together with thermal expansion, melting land ice and natural 
variability, to achieve reliable regional sea-level and climate prediction."

A recent comprehensive review of of sea-level rise by Cazenave & Llovel 
(Annual Reviews of Marine Science 2010) considers an earlier paper by 
Rahmstorf (2007) which like the recent Vermeer & Rahmstorf (2009) 
produced comparable values of between 50 and 120cm by 2100, describing 
it as "offering plausible ranges of future sea-level rise and an 
interesting alternative to still uncertain coupled climate model 
projections.".

Also, if it is indeed "widely accepted" as you say, that the IPCC AR4 
(AB1) scenario for future globally averaged sea-level rise is a serious 
underestimation then why for example do the eminent scientists of the 
Royal Society (Climate change: a summary of the science. Sept 2010) not 
share these views? There is no evidence that they accept the large 
values that you cite, quite the contrary. They conclude that "Because of 
the thermal expansion of the ocean, it is very likely that for many 
centuries the rate of global sea-level rise will be at least as large as 
the rate of 20 cm per century that has been observed over the past 
century." and "There is currently insufficient understanding of the 
enhanced melting and retreat of the ice sheets on Greenland and West 
Antarctica to predict exactly how much the rate of sea level rise will 
increase above that observed in the past century for a given temperature 
increase."

This is, and remains an area of considerable uncertainty and controversy 
and I dare say will remain so until a reliable longer term dataset has 
accumulated. In the meantime we should be cautious to oversimplify the 
issues involved and close our minds to all the alternatives.

Richard P Dunne




On 03/10/2010 05:08, Paul Blanchon wrote:
> Dear Richard and list,
>
> The argument that some atolls  "may survive for generations"  and
> should be considered for re-population seems just a little absurd,
> regardless of the politics.
> It is widely accepted that not only is the IPCC AR4 prediction of SL
> rise a serious underestimation, but that over the last few decades
> "...sea level has in fact risen 50% more than predicted by its
> models..."  (see the illuminating climate-science blog at:
> www.realclimate.org/index.php/archives/2010/03/ippc-sealevel-gate/).
>
> The IPCC underestimation has been the subject of several subsequent
> publications which all conclude SL rise by 2100 will likely exceed one
> meter: for example, Vermeer and Rahmstorf 2009 (PNAS 106: 21527-21532)
> predict average rates over the 21st century will be 8-18 mm/year.
> Thus, as Chip Fletcher implies, the experience of Micronesians is
> likely to be repeated in all low-lying coastal communities, regardless
> of past or future regional variation.
>
> Re-population of any atoll would therefore seem to be an exceptionally bad idea.
>
> Saludos,
> Paul.
>
> Paul Blanchon
> Marine Geoscience Lab.,
> Reef Systems Unit,
> Institute of Marine Sciences&  Limnology
> National Autonomous University of Mexico
> Tel. +52  (998) 87-10009 Ext 166
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