North Atlantic warming hole, illustration. Also known as the 'cold blob' (blue, upper centre), this cold temperature anomaly of ocean surface waters is thought to be caused by climate change-induced melting of the Greenland ice sheet. It is shown affecting the western part (below Greenland) of the North Atlantic Drift, the north-eastward extension of the Gulf Stream (red). Also shown is the North Atlantic Deep Water (blue, cold deep water). The latter current forms as the waters of the branches of the North Atlantic Drift cool and sink off Norway and Greenland. Together, these currents are the Atlantic part of the global thermohaline circulation that distributes heat round the world's oceans. Here, it is responsible for the temperate climate of north-western Europe and disruption of this circulation could cause more extreme weather along with colder winters and summers. For this illustration without the cold blob, see image C047/4535. For alternate illustration of the cold blob, see images C047/4536 to C047/4538.