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Modern increase not a temperature swing: scientists
A new study has found that water flowing from the Atlantic Ocean into the Arctic is warmer than it's been in 2,000 years.
The increased heat input has "far-reaching consequences" and is likely helping fuel the remarkable change underway at the top of the planet, European and U.S. scientists report in the journal Science today.
"We find that early 21stcentury temperatures of Atlantic water entering the Arctic Ocean are unprecedented over the past 2,000 years," say the scientists. They studied the Fram Strait branch of the North Atlantic Current, the major ocean conveyor that carries heat north from the tropics.
It cuts between Greenland and Norway, and is "by far the biggest input into the Arctic," says team leader Robert Spielhagen, of Germany's Academy of Sciences, Humanities and Literature.
The water flows counterclockwise around the Arctic Ocean, and he says it is sure to be contributing to the Arctic meltdown that has seen record ice retreat and warming in recent years.
Annual average air temperatures have climbed almost 3C at the Eureka weather station in Canada's High Arctic since 1972, a trend seen across much of the North, which is breaking records again this winter. In December, sea-ice extent was the lowest on record since 1979, and temperatures were above average in much of the Arctic.
To understand what is happening, scientists say they need a better read on the long-term natural variation in the currents flowing north.
Few records go back more than 150 years, so Spielhagen's team pulled up sediments from the sea floor that contain remains of organisms living and dying in the water over the eons.
By studying the tiny-shelled organisms called foraminifera, which grow best under specific conditions, they could chart temperatures going back 2,000 years.
Their sampling site was 1,500 metres below the water surface and under the path of Atlantic water flowing to the Arctic Ocean.
They report the water has warmed about 2C since the late 1800s. The top few centimetres of sediment, representing the past 10 to 20 years, corresponds with a summer temperature of 6C, which matches what is seen in the northbound current.
The scientists say the data indicates the modern warming is not just the latest natural variation. The modern warming is "unequalled" by anything in the past 2,000 years, including the warm period seen in Roman and medieval times that affected climate in northern Europe and North America.