Climate change: But cooler in Europe?

Climate rocker in the Atlantic could slow down the temperature rise in the north

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Europe could face a slightly cooler future than predicted by the IPCC. That's what scientists now conclude from a new analysis of the climatic swings of the last 10, 000 years. It showed that the temperatures between the North and South Atlantic Ocean behave like a seesaw: Warm periods in the south usually correspond to cooler phases in the north.

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Swedish researchers from the Lund University around Svante Bj rck, Karl Ljung and Dan Hammarlund have taken and analyzed drill cores from lake sediments and swamps of Atlantic islands in the North and South Atlantic for their new study. The series of samples began in Greenland and then reached Iceland, the Azores and Faroe Islands via Tristan da Cunha, the Isla de los Estados to the Antarctic Peninsula. Based on geochemical and magnetic analyzes, as well as the pollen content, the researchers gained previously unknown details of Atlantic climate development. The temporal resolution of the new data is much higher than that of all previous investigations.

Climate rocker in the Atlantic

The results show that after the end of the last ice age both hemispheres warmed up first. "But during the last 9, 000 years, we can identify an ongoing 'swing' pattern, " explains Björck. "When the South Atlantic was warm, it was cold in the north and vice versa."

According to the researchers, this pattern is closely linked to the large-scale circulation of the Atlantic, the great "assembly line of the sea". It is driven by the sinking of cold salty water in the northern North Atlantic. The water then flows south in depth and is continually being replaced by sinking surface water. At the same time warm water flows from the South Atlantic on the surface to the north. The Gulf Stream and the North Atlantic Current in turn allow Europe to benefit from a mild climate. display

The sinking of surface water in the North Atlantic depends heavily on the surface temperatures of the sea and its salinity. Melting glaciers or heavy precipitation "dilutes" the water and thus inhibits the "pump". As a result, less warm water flows to the north and the climate is cooler. Such anomalies often occurred after the last ice age and have also occurred on a smaller scale in modern times: In the 1970s, the "Great Salt Anomaly" made sure that the cod population in front of the Faroe Islands dropped significantly - the water became too cold.

The south is already warming up

For the first time, the new study has revealed clear evidence of warming in the South Atlantic, in the area of ​​the Tristan da Cunha archipelago between South Africa and Argentina, and has demonstrated correlations to a cooling of the North Atlantic. The researchers are not worried about a complete failure of the North Atlantic pump and thus of the warm ocean currents in the north, but it is very likely that climate change will influence the "seesaw".

"We do not know for sure what will happen, " explains Björck. "Some studies of the ocean currents indicate a weakening of the Gulf Stream. Also, the transport of heat into the North Atlantic could slow down as a result of increased rainfall in the future. Such a scenario would lower global warming than predicted by the IPCC. However, we will not have to worry about an Arctic climate. "

(Lund University, May 2, 2007 - NPO)