Environment

Arctic warming

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Arctic temperatures in the 1990s reached their warmest level of any decade in at least 2,000 years, despite a gradual cooling trend over that time as the Earth cycled further away from the sun. A new study being published in Science Magazine tomorrow concludes that the cooling was reversed because of increased emissions of carbon dioxide and other green house gases. The World’s Katy Clark reports.

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MARCO WERMAN: I’m Marco Werman and this is The World, a co-production of the BBC World Service, PRI, and WGBH Boston. The Arctic is heating up and there’s new evidence to confirm that humans are to blame. A study coming out tomorrow in the Journal of Science looks at 2000 years of temperature records. They show that the Arctic was undergoing a predictable cooling trend for most of that time but that abruptly changed in the twentieth century. The World’s Katy Clark has more.

KATY CLARK: The study’s lead author, Darrell Kaufman of Northern Arizona University, says news that temperatures fluctuate in the Arctic isn’t new. We knew for instance the region was fairly warm after the retreat of the last big ice sheets about 8000 years ago.

DARRELL KAUFMAN: And we’ve known that the temperatures in the Arctic have cooled since then culminating in the period known as the little ice age between about 1500 and 1900 AD.

CLARK: That cooling which continued into the last century was caused by a natural wobble in the earth’s orbit around the sun. That process is still going on so you’d expect the cooling to continue. Instead though, Kaufman and his colleagues found that by the 1990s the cooling had reversed. By the year 2000 summer temperatures in the Arctic were about two and a half degrees warmer than expected. David Schnieder is a climate scientist with the National Center for Atmospheric Research in Colorado and one of the study’s co-authors. He says looking at 2000 years of temperature data put the changes into perspective.

DAVID SCHNIEDER: It emphasizes the fast pace of the current change versus the slow natural changes.

CLARK: The researchers decipher the Arctic’s climate history by looking at natural records including lake sediments. Again Darrell Kaufman.

KAUFMAN: Most of the lakes that we studied are located downstream of modern-day glaciers. As summer temperatures increase the amount of melt water that was generated by those glaciers also increased and the melt water is what carries the sediments to the lake and it shows up as a thicker layer of mud across the lake during years with more melt water.

CLARK: The information from the lake sediments was then matched up with similar natural data from tree rings and ice cores. Each showed the same overall cooling trend until recently. Finally all those findings were compared with computer models of what would happen with increasing levels of greenhouse gases. The results convinced the scientists that the recent warming could only have been caused by human activity. The warming in the Arctic is generally more pronounced than in the rest of the world. That’s due to unique feedback systems in the region. For instance warmer temperatures cause sea ice to melt. That leaves more open water. Water in turn absorbs more heat than ice which results in even warmer temperatures. So what does this study tell us about our future? David Schnieder says for one thing we’ll probably be looking at an ice-free Arctic in the summers within 100 years. It could also mean trouble for other parts of the north.

SCHNIEDER: You would expect more land ice to melt like in Greenland and in smaller ice caps that are scattered around the Arctic. So in that way if this trend continues it will be leading to more glacier melt.

CLARK: And that could potentially have a big impact on sea levels. Ultimately the new research only adds to the already strong evidence that the planet is warming up and that humans are responsible. Those who have been warning about climate change for a while though don’t expect the study will stir politicians who’ve been on the fence about climate change legislation. Nikki Roy is with Pew Center on Global Climate Change.

NIKKI ROY: The Arctic is the … . It’s a canary in the coalmine. We have no shortage of canaries in this particular coal mine but it certainly one of the biggest.

CLARK: And Roy says this study is just another piece of evidence adding to the urgency. For The World this is Katy Clark.

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