What’s going on in the North Atlantic? « RealClimate
►http://www.realclimate.org/index.php/archives/2015/03/whats-going-on-in-the-north-atlantic
The North Atlantic between Newfoundland and Ireland is practically the only region of the world that has defied global warming and even cooled. Last winter there even was the coldest on record – while globally it was the hottest on record. Our recent study (Rahmstorf et al. 2015) attributes this to a weakening of the Gulf Stream System, which is apparently unique in the last thousand years.
The whole world is warming. The whole world? No! A region in the subpolar Atlantic has cooled over the past century – unique in the world for an area with reasonable data coverage. So what’s so special about this region between Newfoundland and Ireland?
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What are the impacts of a slowdown?
Meltwater on the Greenland ice sheet.The consequences of a large reduction in ocean overturning would look nothing like the Hollywood film The Day After Tomorrow. But they would not be harmless either – e.g. for sea level (Levermann et al. 2005) particularly along the US east coast (Yin et al. 2009), marine ecosystems, fisheries and possibly even storminess in Europe (Woollings et al. 2012). We have studied these consequences some years ago in an interdisciplinary project with colleagues from Bremerhaven, Hamburg and Norway – the results are summarized in Kuhlbrodt et al. 2009.
If our analysis is correct, then this indicates that climate models underestimate the weakening of the Atlantic circulation in response to global warming – probably because the flow in these models is too stable (see Hofmann and Rahmstorf 2009). Although these models predict a significant weakening for the future, they do not suggest this as early as the observations show it (see Fig. 2 of our paper). That the real flow may be more unstable than previously thought would be bad news for the future.
If the circulation weakens too much it can even completely break down – the AMOC has a well-known “tipping point” (Lenton et al., 2008).
▻https://www.youtube.com/watch?v=3niR_-Kv4SM
NASA: The Thermohaline Circulation (The Great Ocean Conveyor Belt)