The lack of substantial warming in the ocean around Antarctica is a result of overturning circulation that brings cold water up from the depths, reports a paper published online in Nature Geoscience. The findings suggest that the timescale for Southern Ocean warming will be on the order of several centuries - the amount of time it takes for the temperature of deep water to change.

At millennial timescales, warming in both polar regions - the Arctic and the Southern Ocean - has occurred faster than the global average. However, since 1950 only minimal warming has been observed in the Southern Ocean around Antarctica, whereas further north, at the flank of the Antarctic Circumpolar Current closest to the equator, temperatures have risen substantially.

Kyle Armour and colleagues analysed ocean observations and climate model simulations to show that Southern Ocean temperature changes are governed by the meridional overturning circulation. Specifically, they find that the winds around Antarctica bring up relatively cold water from the depths, while simultaneously pushing warm surface waters towards the equator. They conclude that, as a consequence, warming around Antarctica in response to greenhouse gas emissions is expected to occur over centuries or longer, over the same timescales that are required to warm the deeper layers of the ocean.