Greenland Ice Sheet changes; new Fettweis paper

The old man has been recovering recently, so a lot of discussion has gone by the board; apologies if this has already been discussed.

Fettweis et. al. have a new paper under discussion in The Cryosphere (Copernicus open access). Link here. if that doesn’t work, try: http://www.the-cryosphere-discuss.net/2/225/2008/tcd-2-225-2008.pdf 

The conclusion (which has a large uncertainty), based on a modelling of the GrIS surface mass balance fron 1900 -2100, using the AR4 GCMs, is that the contribution to sea level rise is likely to be around 4cm by 2100. This, however, assumes no change in the rate of iceberg calving or basal sliding.

It also derives from an analysis of the models which shows a temperature increase in Greenland (area 1) of around 2 degrees, which is offset by greater precipitation.

Apart from concern over the idea that calving and sliding is likely to remain consistent (I’d suggest that reactions are more likely to be non-linear), there is the question of the implications of findings such as Rignot’s on the changes in key discharge glaciers.

An interesting and challenging conclusion of the reanalysis is that there were more rapid changes in the 1930s than there have been recently (which would be consistent with the Jones et al temperature analyses). This might suggest to a cynic that the impacts of AGW are within natural boundaries (& therefore, supposedly, not a matter for concern). This, though, ignores the cumulative effect of the changes over the longer time scale, a flaw which also appears to be in the paper.

I have some doubts about the Fettweis material, but am not qualified to say more than this; perhaps a Connolley or a Benestad can help explain what the paper appears to be missing. My suggestion is that, whilst this is a comprehensive and scientifically sound piece of work on the surface, there are some assumptions embedded within it which might not be sustainable given other work which the paper does not consider.

It also occurs to me that a change in accumulation to compensate for mass loss through melting, whilst it would help stabilist the GrIS mass balance, does not reduce the rate of melting per se; therefore, it may be that Fettweis’s SLR estimate is much too low.

I’d appreciate it if spome of you read the actual paper and gave us some hints where we (or Fettweis) are going wrong.

I’m still cnsidering the prospect of a global SLR of a metre or more, with a GrIS contribution of perhaps 10-20% by the end of the century.