By Stefan Rahmstorf
24 January 2016
(RealClimate) – Blizzard Jonas on the U.S. east coast has just shattered snowfall records. Both weather forecasters and climate experts have linked the high snowfall amounts to the exceptionally warm sea surface temperatures off the east coast. In this post I will examine a related question: why are sea surface temperatures so high there, as shown in the snapshot from Climate Reanalyzer above?
I will argue that this warmth (as well as the cold blob in the subpolar Atlantic) is partly due to a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), sometimes referred to as the Gulf Stream System, in response to global warming. There are two points to this argument:
(1) The warm sea surface temperatures are not just some short-term anomaly but are part of a long-term observed warming trend, in which ocean temperatures off the U.S. east coast are warming faster than global average temperatures.
(2) Climate models show a “cold blob” in the subpolar Atlantic as well as enhanced warming off the US east coast as a characteristic response pattern to a slowdown of the AMOC. […]
In our paper in Nature Climate Change last year (see our Realclimate post on this) we used sea surface temperature data specifically from the cold blob to diagnose AMOC variations and found an exceptional AMOC slowdown in the 20th Century, and we argued that Greenland mass loss may have made a significant contribution to this slowdown by helping to dilute ocean waters in the subpolar Atlantic. [more]