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Department of Biological Sciences (BIO)

Recent warming reverses long-term Arctic cooling

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 work presented in this paper is based on the publications from the "Arctic Lakes 2k project" published in Journal of Paleolimnology Special Issue, "Late Holocene Climate and Environmental Change Inferred from Arctic Lake Sediment" volume 41:1 in 2009. The work includes reconstructions of past July temperatures from northern Norway and northern Finland done by John Birks and Anne Bjune from Dept. of Biology and Bjerknes Centre for Climate Research, University of Bergen, in conjunction with Heikki Seppä in Finland.

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