Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation

[Martijn]

De Atlantic meridional overturning circulation (AMOC) is een circulatie in de Atlantische Oceaan die gekenmerkt wordt door een noordwaartse stroming van warm, zout water in de bovenste lagen van de Atlantische Oceaan (waaronder Golfstroom en Noord-Atlantische Drift) en een zuidwaartse stroming van kouder water in de diepere lagen van de Atlantische Oceaan.

Volgens onderstaande studie zijn er aanwijzingen dat de AMOC trager wordt, wat een verklaring kan zijn voor een afkoeling in de Noord-Atlantische Oceaan. Dit kan invloed hebben op het klimaat van West-Europa. Het smelten van de ijskap op Groenland zou een mogelijke oorzaak van de AMOC kunnen zijn en wordt besproken in de publicatie.

Bron: http://www.nature.com/nclimate/journal/ ... e2554.html

Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation

Stefan Rahmstorf, Jason E. Box, Georg Feulner, Michael E. Mann, Alexander Robinson, Scott Rutherford & Erik J. Schaffernicht

Nature Climate Change 5, 475–480 (2015)
doi:10.1038/nclimate2554

Received: 14 July 2014
Accepted: 28 January 2015
Published online: 23 March 2015

Abstract

Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p > 0.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.

De volledige tekst van de publicatie is gratis beschikbaar op researchgate.net:
http://www.researchgate.net/publication ... irculation

[Martijn]

Stefan Rahmstorf, één van de auteurs van de studie, heeft er onderstaand artikel over gepubliceerd.

Bron: http://www.realclimate.org/index.php/ar ... -atlantic/

What’s going on in the North Atlantic?

Filed under: Climate Science — stefan @ 23 March 2015

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 (Fig. 1). So what’s so special about this region between Newfoundland and Ireland?

Fig. 1 Linear temperature trend from 1900 to 2013. The cooling in the subpolar North Atlantic is remarkable and well documented by numerous measurements – unlike the cold spot in central Africa, which on closer inspection apparently is an artifact of incomplete and inhomogeneous weather station data.

Rahmstorf_2015_1rc.jpg (47.44 KiB) 5261 keer bekeken

It happens to be just that area for which climate models predict a cooling when the Gulf Stream System weakens (experts speak of the Atlantic meridional overturning circulation or AMOC, as part of the global thermohaline circulation). That this might happen as a result of global warming is discussed in the scientific community since the 1980s – since Wally Broecker’s classical Nature article “Unpleasant surprises in the greenhouse?” Meanwhile evidence is mounting that the long-feared circulation decline is already well underway.

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Zie bron voor volledig artikel.