RT Journal Article SR Electronic T1 Pliocene Warmth, Polar Amplification, and Stepped Pleistocene Cooling Recorded in NE Arctic Russia JF Science JO Science FD American Association for the Advancement of Science SP 1421 OP 1427 DO 10.1126/science.1233137 VO 340 IS 6139 A1 Brigham-Grette, Julie A1 Melles, Martin A1 Minyuk, Pavel A1 Andreev, Andrei A1 Tarasov, Pavel A1 DeConto, Robert A1 Koenig, Sebastian A1 Nowaczyk, Norbert A1 Wennrich, Volker A1 Rosén, Peter A1 Haltia, Eeva A1 Cook, Tim A1 Gebhardt, Catalina A1 Meyer-Jacob, Carsten A1 Snyder, Jeff A1 Herzschuh, Ulrike YR 2013 UL http://science.sciencemag.org/content/340/6139/1421.abstract AB Climate and the atmospheric concentration of CO2 are closely linked. Brigham-Grette et al. (p. 1421, published online 9 May) present data from Lake El'gygytgyn, in northeast Arctic Russia, that shows how climate varied between 3.6 and 2.2 million years ago, an important interval in the global cooling trend that accelerated rapidly at the end of the Miocene. Summer temperatures were about 10°C warmer than today, even though the concentration of atmospheric CO2 was similar. Understanding the evolution of Arctic polar climate from the protracted warmth of the middle Pliocene into the earliest glacial cycles in the Northern Hemisphere has been hindered by the lack of continuous, highly resolved Arctic time series. Evidence from Lake El’gygytgyn, in northeast (NE) Arctic Russia, shows that 3.6 to 3.4 million years ago, summer temperatures were ~8°C warmer than today, when the partial pressure of CO2 was ~400 parts per million. Multiproxy evidence suggests extreme warmth and polar amplification during the middle Pliocene, sudden stepped cooling events during the Pliocene-Pleistocene transition, and warmer than present Arctic summers until ~2.2 million years ago, after the onset of Northern Hemispheric glaciation. Our data are consistent with sea-level records and other proxies indicating that Arctic cooling was insufficient to support large-scale ice sheets until the early Pleistocene.