"The human-driven buildup of heat-trapping greenhouse gases in the atmosphere appears to have ended a slide, many millenniums in the making, toward cooler summer temperatures in the Arctic, the authors of a new study report.
Scientists familiar with the work, to be published Friday in the journal Science, said it provided fresh evidence that human activity is not only warming the globe, particularly the Arctic, but could also even fend off what had been presumed to be an inevitable descent into a new ice age over the next few dozen millenniums.
The reversal of the slow cooling trend in the Arctic, recorded in samples of layered lakebed mud, glacial ice and tree rings from Alaska to Siberia, has been swift and pronounced, the team writes."
Andrew C. Revkin reports for the New York Times September 3, 2009. 
"Humans May Have Ended Long Arctic Chill" (Dot Earth) 
"Emissions Linked to End of 2,000-Year Arctic Trend" (Washington Post)