The Atlantic current system which maintains mild weather in Europe is at its weakest in over a millennium, most likely because of climate change, scientists have found.
The Atlantic Meridional Overturning Circulation is part of a system of ocean currents which acts as a conveyor belt to move water around the Earth, redistributing heat and acting as a key link in maintaining the world’s climate.
It began a serious slowdown around 1850 and is now at its lowest point in 1,000 years, according to a new study in the journal Nature Geoscience.
It is not certain what the impact of further weakening will be on weather patterns, but scientists believe it could bring more heatwaves in Europe, and sea level rise on the east coast of the US.
The impact of changing water temperatures is also potentially devastating for some marine life, with the slowdown already linked to lower cod numbers off Maine.
Some evidence suggests there could be a ‘tipping point’ sometime after 2100 when the system collapses, which could cause intense winter storms in Europe and a significant cooling effect across the northern hemisphere that would not be offset by global warming.
Co-author Dr David Thornalley, from University College London said: “This study shows the increasing evidence in support of the modern Atlantic Ocean undergoing unprecedented changes in comparison to the last millennium, and in some cases longer.”
Scientists from Ireland, Britain and Germany looked at 11 different sources of data, including tree rings, ocean sediment and corals.
The AMOC has only been directly measured since 2004, leaving scientists to rely on indirect measurements such as these to monitor historic change, which produce imprecise results.
Dr Laura Jackson, a Met Office scientist specialising in AMOC who was not involved in the study, said there were “still uncertainties associated with using these indirect observations.”
But the paper adds to previous research that found a weakening of the AMOC, with one study suggesting there has been a 15 per cent decrease since the mid-century.
Climate change models assume a slowing of the AMOC, because the water is driven by its density, which is due to low temperatures and salinity.
Both of these are expected to change as greenhouse gases warm the atmosphere and melting ice and increased rainfall reduces saline content.
Dr Andrew Meijers, Deputy Science Leader of Polar Oceans at British Antarctic Survey, said: “The AMOC has a profound influence on global climate, and particularly in North America and Europe, so this evidence of an ongoing weakening of the circulation is critical new evidence for the interpretation of future projections of regional and global climate.”
But Tim Palmer, a Professor in Climate Physics at the University of Oxford, cautioned that “The extent to which AMOC variability affects European weather is a matter of great uncertainty, as there are many other drivers for variations in European weather, including atmospheric chaos.”
He added: “Overall, this is an interesting study and one that needs continued investigation. However, it shouldn’t be over-interpreted.”