Arctic temperatures hit 2,000-year high


"The 1990s were the Arctic's warmest decade in the past 2,000 years, says a study released in Friday's edition of Science. The warming -- due to the release of greenhouse gases into the Earth's atmosphere -- overpowered a natural cooling trend that should have otherwise continued.

Scientists used "natural" thermometers -- such as glacial ice cores, tree rings and sediments from lakes -- to calculate the temperatures of the Arctic over the past two millennia. Instruments have been used to measure the actual temperature of the Arctic since the late 1800s.

"This study provides us with a long-term record that reveals how greenhouse gases from human activities are overwhelming the Arctic's natural climate system," reports study co-author David Schneider of the National Center for Atmospheric Research (NCAR) in Boulder, Colo.

In the decade of the 1990s, Arctic temperatures measured about 2.5 degrees F higher than they would have had the cooling continued.

The Arctic's gradual cooling trend is due to a wobble in the tilt of the Earth, which, over the last 7,000 years, has shifted the Earth's closest pass by the sun from September to January. This reduces the intensity of the sunlight that reaches the Arctic in the summer and has caused noticeable cooler summers over the past several centuries. That is, until the effects of global warming took over.

"If it hadn't been for the increase in human-produced greenhouse gases, summer temperatures in the Arctic should have cooled gradually over the last century," says Bette Otto-Bliesner, an NCAR scientist who participated in the study.
"This result is particularly important because the Arctic, perhaps more than any other region on Earth, is facing dramatic impacts from climate change," added Schneider. These impacts include remarkable shrinking of summer sea ice due to the rising temperatures, which reached a record low extent in 2007." (USA Today)