A warm Atlantic linked to hot summers over Europe and US

The Atlantic Ocean plays a much larger role in controlling summer climate in Europe and North America than previously thought, say scientists in a paper published in the journal Science on 1 July 2005.

The scientists, from the NCAS Centre for Global Atmospheric Modelling in Reading, have shown that over the last 100 years several swings in the temperature of the North Atlantic Ocean, each lasting decades at a time, have affected summer climate on both sides of the Atlantic.

Lead author Rowan Sutton said: ‘For the first time we have shown that changes in the Atlantic Ocean can actually drive the climate we experience either side of the Pond. By comparing observations with our results from state-of the-art climate models, we have shown that when the North Atlantic Ocean is warm, summers in the United States are warm and dry, and droughts more frequent. Conversely, when the ocean is cool, U.S. summers are cool and wet. The effects on European summers are more subtle but still important.’

‘Finding this link is extremely important because it allows us to quantify the Atlantic’s role in the climates of border countries. This information should improve our climate forecasts and help us to predict the effects on climate of future changes in the Atlantic Ocean circulation’

‘The swings in Atlantic Ocean temperature are related to variations in a huge overturning circulation known as the thermohaline circulation or Atlantic conveyor belt. Our research suggests that modest changes in this circulation have important effects on summers, not just winters as previously assumed. Bigger changes – in particular a slow down of the circulation – are expected in future in response to man-made global warming.’

The work has allowed the team to make tentative climate predictions for the coming years. Even without taking man-made global warming into account their computer models suggest both the U.S. and Europe could be in for more hot summers, and the U.S. may be facing more summer droughts. ‘But global warming is now a big additional factor,’ cautioned Dr Sutton, ‘and exactly how the effects will add up we don’t yet know.’