More data are needed to determine whether the slowing is a result of human-induced climate change
The marked slowdown in the past decade of the warm Atlantic Ocean currents that bring mild weather to northwestern Europe may be caused by natural variation and not anthropogenic climate change, as has been previously suggested.
The Atlantic Meridional Overturning Circulation (AMOC) is part of the great ocean ‘conveyor belt’ that ceaselessly circulates sea water, heat and nutrients around the globe. In particular, it transports large amounts of warm water from the tropics to the poles, warming the British Isles and maritime northern Europe along the way (see ‘Current affair’). But since 2004, ocean sensors have detected a significant decline in the strength of the currents and a cooling of the subtropical Atlantic as a result. From mid-2009 to mid-2010, for example, the circulation slowed to two-thirds of its usual strength — and some oceanographers suggested that the drop caused the harsh weather in the United Kingdom and western Europe that winter (see Nature 497, 167–168; 2013).