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Risk of rapid North Atlantic cooling this century greater than previously thought

Published: 
10 March 2017
Ocean waves

A study by scientists at the University of Southampton has found there is a 50 per cent probability of rapid cooling of the North Atlantic during the 21st century. Previous projections suggested that, if cooling takes place, it will be over a much longer period of time.

To evaluate the risk of this form of climate change occurring, researchers from the universities of Southampton and Bordeaux developed a new algorithm to analyse 40 climate models, which were originally examined by the Intergovernmental Panel on Climate Change (IPCC). The researchers’ findings are published in the journal Nature Communications.

Sybren Drijfhout, Professor in Physical Oceanography and Climate Physics at the University of Southampton, says: “The possibility of major climate change in the Atlantic region has long been recognised and has even been the subject of the Hollywood movie: The Day After Tomorrow. While no one is predicting the kind of rapid cooling and extreme events seen in the film, our study does sound a warning over climate change and the policies we adopt for the future.”

Current climate models all foresee a slowing of the Meridional Overturning Circulation (MOC) – the phenomenon behind the familiar Gulf Stream, which carries warm water from Florida to European shores. Slowing of MOC could lead to a dramatic, unprecedented disruption and cooling of the climate system.

Illustration of rapid cooling in gyre predicted by a climate model
Illustration of rapid cooling in gyre predicted by a climate model

In 2013, drawing on 40 climate change projections, the IPCC judged that this slowdown would occur gradually, over a long period of time and that fast cooling of the North Atlantic during this century was unlikely. The Southampton and Bordeaux project team (as part of the EU EMBRACE project), have re-examined these projections by focusing on a critical spot in the northwest North Atlantic, the Labrador Sea – which is host to a convection system (a circular motion of warm and cool water), which feeds into the ocean-wide MOC. The researchers then further focussed on the main factor triggering the convection system, ‘ocean stratification’ – the layering of water of varying densities. Once they isolated relevant models for this, they found 45 per cent predicted a rapid drop in North Atlantic temperatures in the coming century.

In the near future these results can be tested against real data from the Overturning in the Subpolar North Atlantic Program (OSNAP), whose teams will be anchoring scientific instruments within the subpolar gyre (an area of cyclonic ocean circulation). If these predictions are borne out and the North Atlantic waters do cool rapidly over the coming years, climate change adaptation policies for regions bordering the North Atlantic will have to account for this phenomenon. In particular, the predicted global mean temperature increase in 2100 will be 0.5°C less and over the UK more than 1°C less.

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