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.
7 comments
Comments feed for this article
May 4, 2008 at 4:08 pm
William Connolley
I skimmed the paper. I’d say this was a more-of-the-same kind of paper; youll never get very exciting changes without throwing in some major calving/sliding type stuff, and that isn’t in the current (GCM) models. Mind you I’m not saying that it *will* cause large ice oss; only that you can’t get much without it.
May 4, 2008 at 6:56 pm
fergusbrown
This is pretty much what I thought, but then what’s the point of the paper?
If they’re not going to look at the stuff which makes a difference, there won’t be much of a difference to see.
Thanks for looking, anyway.
May 7, 2008 at 9:38 pm
Aaron Lewis
The other thing that is not in the paper and is not in GCM is “small scale” weather patterns driven by temperature differentials between warm ocean waters (or the latent heat over them) and ice. These weather patterns can produce substantial amounts of rain. Rain melts thin ice, and causes structurally failure in thick ice.
I am disappointed that there is no foundation engineering analysis of the strength of the basement ice.
The temperature anomaly in the 1930s was brief. The effect was like your turbine installer tossing you a wrench from form 8 feet above you. You can catch it easily. However, if he is on a tower 80 feet high above you, then catching the thrown tools is going to cause some pain. That is: the longer Greenland melts, the more pain it is going to cause, and the function is not linear. Moreover, WAIS and EAIS want to start tossing us stuff also.
Climate science is like a beautiful silk carpet. GIS, WAIS, and EAIS are a nasty lump under that carpet that nobody has talked about since Newt Gingrich grabbed the EPA’s purse strings 20 years ago.
It is time for Newt to face up to the consequences of his actions.
May 8, 2008 at 6:58 am
Greenland » Do your bit for Greenland - drive your 4x4 around.
[...] Greenland Ice Sheet changes; new Fettweis paperIt 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 … [...]
May 19, 2008 at 10:02 pm
Aaron Lewis
http://stratus.ssec.wisc.edu/products/rtpolarwinds/modis/NTERRA11.GIF for May 19, 2008, 15:34 GMT
Hang on to your hat. That link shows a local weather event pumping heat from the open water of the Davis Straights onto the Greenland Ice sheet.
January 11, 2009 at 4:24 pm
Charles Higley
There is a fly in the ointment: “the summer temperature at the Summit of the Greenland ice sheet shows a decreasing tendency since the beginning of the measurements in 1986 (Chylek et al., 2004).” And it does not melt up there. They also note that “the Greenland warming of 1920 to 1930 demonstrates that a high concentration of carbon dioxide and other greenhouse gases is not a necessary condition for [a] period of warming to arise,” and that “the observed 1995-2005 temperature increase seems to be within [the] natural variability of Greenland climate.”
The warm period of the early 20th century was 1906-1956, not particularly brief by any measure. There was a spike in this already warm period in the mid to late ’30′s. The point here is that only in 1973 and around 1998 have we been in the temperature range of this 50 year period and we are not close to it now, and going down again, fluctuating up and down with a general, small, century-scale trend upwards. We are on a downward trend for now.
This is based on temperature data from consistently rural sites in the US, which has the best records on the planet. It can be argued that for such a large, mid-latitude landmass, its trends will be fairly indicative of the planet. The warm trend shown by the IPCC’s global temperature shows a warm period, albeit smaller in the 1920′s to 30′s, cooling to the late 70′s and a rapid, larger warming ever since.
If you note that more than half of the temperature monitoring sites have vanished in the last 30+ years, mainly the loss of rural sites, the enrichment of sites showing urban heat island effect, which is also an ever growing effect, their graph begins to make sense.
The number of stations was about 15,000 in 1970, which declined to about 12,000 by 1989, rapidly decreased to about 6500 by 1993 (collapse of the Soviet Union?), and declined steadily to about 5000 by 2000. An honest sifting of the monitoring sites and a check of all of their maintenance and quality is required, not adjustment of the data, to fix this discrepancy.
An interesting observation was made by Drake at (http://homepage.ntlworld.com/jdrake/Questioning_Climate/_sgg/mm_1.htm} in which he correlated numbers of stations with temperature and there is a very interesting result that, at least, suggests that there is something critical going on here.
As cities continue to grow, the loss of outlying stations and increased urban effects, the augmented warming seen in the IPCC global record is entirely expected. It could be argued that urban heating could warm the planet, but calculations have thus far indicated that this would be negligible at current levels.
From this and the fact that there is simply too little CO2 to have any credible effect on the climate (water vapor rules) and that our contribution to the annual CO2 is Lilliputian (the half-life of CO2 in the atmosphere is only 5-10 years, regardless of the IPCC’s need for it to be 200 years), I wonder what the worry is. I am, of course, ignoring the political needs for global warming, in which there is a great need by some countries, groups, and individuals to develop power over others by making it their fault for the climate.
January 19, 2009 at 6:23 pm
Eli Rabett
While cities continue to grow, the countryside and small towns empty. This happened early in France.