Another climate-related manuscript on the Nature peer review trial: Land-ice melting causes strong multi-century slowdown of Atlantic circulation even under 2xCO2 stabilisation. It looks basically fine in scientific terms and therefore I'm pretty sure that it will get published. They show that for their GCM, a 2xCO2 stabilisation scenario with a rapid Greenland melt included causes the MOC to decline and stay weak for 500 years.
The only thing that surprises me a bit is that it got through the Nature "is it exciting" editorial filter in the first place. The results don't seem particularly unexpected, and indeed aren't very different from their recent GRL paper, although they have extended the analysis somewhat. The model they use has a particularly weak MOC for the present day compared both to observations and other model results, and they simulate a rather extreme rate of Greenland melting over the next 500 years (both qualitative assessments are the authors' own, so I'm not being narky here). It certainly doesn't surprise me that the resulting freshwater input slows down the MOC considerably (and when I presented these premises to jules in a "blind test" without telling her the answer, she got it spot-on too). There is no rapid "day after tomorrow" shutdown, and the end result is merely less warming (not just regionally, but a little less globally too) than without the melt. The most "exciting" outcome in terms of human impact is probably the rapid sea level rise of up to 11mm per year, but that is simply the consequence of their high melt rate.
We have already seen how uncertain the long-term MOC is, and how strongly it can depend both on its initial ("present day") level and the magnitude of the freshwater forcing. (Of course that paper is just one investigation using a simpler model. Although I'm flattered to see that it has been top of the download charts ever since publication I would hardly claim it is a seminal contribution to the field, eg see here for much more.). And it makes little difference whether the fresh water hosing is due to increased precipitation in the region, or ice melting. So I look forward to seeing what the headline-writers make of this new contribution...
The only thing that surprises me a bit is that it got through the Nature "is it exciting" editorial filter in the first place. The results don't seem particularly unexpected, and indeed aren't very different from their recent GRL paper, although they have extended the analysis somewhat. The model they use has a particularly weak MOC for the present day compared both to observations and other model results, and they simulate a rather extreme rate of Greenland melting over the next 500 years (both qualitative assessments are the authors' own, so I'm not being narky here). It certainly doesn't surprise me that the resulting freshwater input slows down the MOC considerably (and when I presented these premises to jules in a "blind test" without telling her the answer, she got it spot-on too). There is no rapid "day after tomorrow" shutdown, and the end result is merely less warming (not just regionally, but a little less globally too) than without the melt. The most "exciting" outcome in terms of human impact is probably the rapid sea level rise of up to 11mm per year, but that is simply the consequence of their high melt rate.
We have already seen how uncertain the long-term MOC is, and how strongly it can depend both on its initial ("present day") level and the magnitude of the freshwater forcing. (Of course that paper is just one investigation using a simpler model. Although I'm flattered to see that it has been top of the download charts ever since publication I would hardly claim it is a seminal contribution to the field, eg see here for much more.). And it makes little difference whether the fresh water hosing is due to increased precipitation in the region, or ice melting. So I look forward to seeing what the headline-writers make of this new contribution...
8 comments:
Would you please define your fucking acronyms? Not everyone is as steeped in this paper as you are. Do you want your readers to understand what you are talking about or not? Get a clue.
Despite the way you ask:
For GCM see Global_climate_model
For MOC see Thermohaline_circulation
Both can now be found by looking up GCM or MOC
crandles
Anon,
Would you have written that under your full name, or if you knew your mother reads this blog?
Thanks for the refs Chris. I suppose MOC is still a little uncommon, with the slightly inaccurate THC still more popular.
Annan & Hargreaves once again bet the house that a future anthropogenic-induced warming will match their paleo twaddle performed with poor modelling. And bitches about anyone who dares show it ain't necessarily so...
I'm not sure what planet you are calling in from, anon, but if you'd got through the post before you started frothing, you might have noticed that my point was precisely to say that this new manuscript is entirely consistent with what is already understood about model behaviour...of which our own work is only one very small part.
There is something deeper going on here. The basic idea made the national radio news in the US
Eli,
Interesting link, but the basic idea is not at all new. I think it got a bit of recent impetus with some ice cap observations, and of course there was the Bryden thing (which as far as I can tell no-one actually believes, but it's a useful hook to hang stories on). So I guess it is topical, but this modelling experiment is rather extreme and the results seem unexceptional.
Actually I was going more in the direction that someone was stirring the publicity pot.
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