The UK’s run of rain-drenched summers could be ended by a slow-down in major Atlantic currents which bring warm, wet air to Europe, according to research. The currents were known to have weakened since 2004 but the new work suggests the trend began in the 1990s and shows no sign of ending. However, the scientists said the changes to summer weather would take a decade or more to unfold. Professor Rowan Sutton, at the University of Reading and part of the research team, said: “Those of us that spend our summer holidays in Britain would welcome a move away from a recent succession of soggy summers. But this research certainly isn’t a forecast for summer 2014, or any other year.” He said the changes to UK climate would be in addition to the longer-term global warming trend driven by carbon emissions, which is most likely to bring an increase in heatwaves and extreme storms.
The system of surface and deep water currents that govern the north Atlantic circulation is called the Atlantic Meridional Overturning Circulation (AMOC). One component of AMOC is the better-known Gulf Stream, which brings warm water northwards and keeps the UK’s climate milder than it would otherwise be. Previous ocean measurements showed AMOC has declined by 10-15% since 2004. But new data from the Labrador sea, a significant part of the AMOC system, and new computer climate modelling, led the researchers to conclude that the “measured decline is not merely a short-term fluctuation, but is part of a substantial reduction in [AMOC] occurring on a decadal timescale.”
Jon Robson, who led the research at the University of Reading, published in the journal Nature Geoscience, said: “Our findings suggest there could be a relative cooling of the North Atlantic sooner rather than later, perhaps over the next decade or so. In Britain we could see a return to drier summers, although it could also lead to more droughts in parts of Europe and Africa. However, there’s quite a bit of uncertainty about how fast changes might happen, and other influences – such as sea ice and greenhouse gase emissions – are also important.” He said the weakening of AMOC could also lead to fewer Atlantic hurricanes.
Sutton added: “A weakening of the AMOC could also mean a decline in the Gulf Stream, although there is currently no evidence that this is happening yet.”
The UK’s run of six wet summers is too short to indicate clearly changes on climate, which evolves over decades, but scientists are following the changes closely as they unfold. The most likely cause of the wet summers are long-term climate cycles in the Atlantic multi-decadal oscillation. Other factors that may be affecting the complex climate system are a shift in the jet stream, a high level wind that channels weather towards the UK, and the fast-retreating sea ice in the Arctic. On top of all these, is the warming effect of the continuing emission of carbon dioxide.
