Radio Script
1998

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Scientists Reconstruct 400 Years of Arctic Climate
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STORY: Even though the thermometer hit minus 40 Fahrenheit in Fairbanks, Alaska, this winter, the Arctic on average is hotter now than at any time in the last 400 years. That's according to an international team of researchers who have reconstructed the Arctic climate over the past four centuries. Jonathan Overpeck is a climatologist with the National Oceanic and Atmospheric Administration.

OVERPECK: "What was really surprising to us was that this century stands out as unprecedented in the last 400 years, and I think in a few longer records we can say that this century stands out as unprecedented in the last 1,200 years, as a period that Arctic-wide was warmer than at any time. Another thing that really surprised us is that the warming that occurred between 1850 and the middle of this century was the only time that the whole Arctic warmed in that fashion."

Since no one was tracking temperatures in the Arctic 400 years ago, researchers used tree rings, gases trapped in glacial ice, and mud samples from lake and ocean bottoms to infer past Arctic warming and cooling periods. Jonathan Overpeck says that before 1850, natural occurrences such as volcanic explosions, which pour sulfur and dust into the atmosphere, cooled the Arctic. Warming periods occurred between volcanic activity and when an unusual sun activity warmed the earth. But he says natural changes aren't enough to explain this latest warming spell.

OVERPECK: "That's the nice thing about what we're trying to do. If you have just data from the 20th century, it gets a little difficult to say for sure what is the natural component and what is the human component. By having a record that extends back centuries, you're able to look at climate variation before humans could have possibly affected climate in the Arctic. From the period between 1600 and 1850 AD, volcanic forcing played a role in causing the inter-annual to decadal-scale variations in Arctic climate. It also appears that the longer-term variations have some connection with variations in the sun. So we're able to conclude that these natural processes play a key role in driving Arctic climate. But our analysis also showed that these natural processes can't explain all of the warming that's occurred in this century. That was probably our most surprising result, that some other process must be playing a role. And the only obvious candidate is greenhouse warming."

Bruce Finney co-authored the study. He's a paleoclimatologist at the University of Alaska Fairbanks, and he blames the industrial revolution, the invention of the internal combustion engine, and other fossil fuel burning activities for today's warmer Arctic.

FINNEY: "That's what most scientists believe, that there's been an acceleration in the carbon dioxide content in the atmosphere that coincides with the industrial revolution and then that is just accelerating as more and more carbon dioxide is put into the atmosphere by automobiles, burning coal, and things like that."

Scientists say the Arctic has warmed about 1 1/2 degrees Celsius, or about 3 degrees Fahrenheit, during the last 100 years or so. That's enough to begin melting permafrost and glaciers. And they say a warmer Arctic might actually trigger a spiraling cycle of warming. As snow cover diminishes, the tundra absorbs even more heat. Thawing peat bogs release trapped greenhouse gases such as methane, which heat the atmosphere and perpetuate the cycle.

OUTRO: For Arctic Science Journeys, this is Robert Hannon reporting from Fairbanks, Alaska.