Global warming to give colder winters and hotter summers

Studies say system of ocean currents that plays vital climate role is losing strength

By Clive Cookson

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Two international research teams have published separate studies in the journal Nature, which together add powerful evidence to fears that the system of ocean currents known as the Atlantic Meridional Overturning Circulation or Amoc is losing strength.

Amoc’s strength has declined by 15 per cent since the mid-19th century and is now at its weakest for at least 1,500 years — and probably since the end of the last big Ice Age 11,500 years ago — said David Thornalley of University College London, lead author of one study by scientists at UCL and Woods Hole Oceanographic Institution.

If the weakening continues, the impact on Europe and the US east coast could be serious. Winter weather is likely to become less stable, with more outbursts of extremely cold air from the Arctic.

It could have the opposite effect in summer. For example, the 2015 European heatwave was paradoxically linked to record cold in northern Atlantic waters that year. That promoted an air pressure system that funnelled warm winds from the south into Europe. Further afield, a weakened Amoc tends to push African rainfall belts southward, increasing the risk of drought in the Sahel.

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