A study published in the online version of the journal Science says human-generated greenhouse gas emissions have helped reverse a 2-thousand year trend of cooling in the Arctic, prompting warmer average temperatures in the past decade that now rank higher than at any time since 1 B.C. One of the report’s co-authors, David Schneider, a visiting scientist at the National Center for Atmospheric Research, says, "It‘s basically saying greenhouse gas emissions are overwhelming the system."

Fred Singer, a prominent climate-change skeptic who heads the Science and Environmental Policy Project, questioned the Science study, saying it does not properly reflect other researchers‘ findings about the Medieval Warm Period. He says, that period, between A.D. 800 and 1300, had - higher temperatures than even the past 30 years. And there was a brief period in the early 5th century in which temperatures in the Arctic came close to being as high as those in the most recent summers.

Mark Serreze, director of the National Snow and Ice Data Center at the University of Colorado at Boulder, said the study is significant because it helps confirm scientists‘ understanding of how Earth‘s climate has changed over millennia.

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