Arctic cooling trend reversed, says report

A new study suggests that climate change has reversed a long-term cooling trend in the Arctic within the past century.

The National Science Foundation-funded study, called Recent Warming Reverses Long-Term Arctic Cooling, published in the 4 September issue of Science, says Arctic temperatures have increased during the past 50 years after cooling steadily from one AD to the year 2000.

Conducted by a team of researchers led by Darrell S Kaufman of Northern Arizona University, the study used samples of lake sediment from several sites north of the sixtieth parallel, along with data from weather stations, to construct a decade-by-decade temperature history of the Arctic Circle. It checked the information against climate modelling data from the National Centre for Atmospheric Research.

During the first 1,900 years, Arctic summer temperatures cooled at 0.2°C per millennium. The cooling was caused by a wobble in the Earth's orbit which left the Arctic slightly further away from the sun.

But by the middle of the 20th century, some Arctic temperatures were 0.7° higher than would have been expected if the gradual cooling trend had continued on its original path.

The data reinforces findings from the 2008 Arctic Report Card, published by the National Oceanic and Atmospheric Administration (NOAA), which said that Arctic temperatures last autumn were at a record 5°C above normal.

Like the Kaufman study, it blamed the temperature rise on the major loss of sea ice, which is set to change the surface of the Arctic, making it darker and causing it to absorb more heat from the sun. The NOAA says that Arctic White warming trend began in the mid-1960s.

However, some contradictory data exists. The Arctic Regional Ocean Observing System, established by 14 European member states, found that ice volume in the Arctic has been rising for the past three years.