Friday, September 4, 2009

Highest Arctic Temperatures in 2000 Years

Images (click to enlarge):
  • 2000 years of Arctic temperatures from Science, via University Corporation for Atmospheric Research
  • Changes in Earth-Sun distance during Arctic summer over time, from National Science Foundation

Midnight Update: Naturally, this research is too important to escape a hatchet job by the anti-science Anthony Wassup site. We don't go there or provide links, because the computer needs to get a tetanus shot after dipping in that bilge. However, the intrepid Tamino is already on the case.

Original post:
A new study published in today's issue of the peer-reviewed journal Science shows that current Arctic temperatures are the highest in the past 2000 years. Based on an analysis of lake sediments and comparisons with previous studies of ice cores and tree rings, the researchers extended the previous record of Arctic climate from 400 years to 2000 years in the past. They found that over the 1900 years prior to the 20th Century, there was a slow rate of cooling in the Arctic. This cooling is consistent with the relationship between small changes in the tilt of Earth's axis and its orbit around the sun. Over the last 7000 years, this has caused Earth's closest approach to the sun to shift from September to January. As a result, the intensity of sunlight in the Arctic summer has been slightly reduced, producing the cooling trend. Over the 20th Century, however, that trend has been overcome by warming which has generated temperatures that are now higher than in the preceding 1900 years. By the year 2000, average Arctic temperatures were 1.4° C (2.5° F) above where they would otherwise have been. Four out of the five warmest decades in the last 2000 years occurred in the 50 years between 1950 and 2000.

The paper's abstract:
The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.
The paper has generated considerable press interest, including:

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