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      Paradoxical cold conditions during the medieval climate anomaly in the Western Arctic

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          Abstract

          In the Northern Hemisphere, most mountain glaciers experienced their largest extent in the last millennium during the Little Ice Age (1450 to 1850 CE, LIA), a period marked by colder hemispheric temperatures than the Medieval Climate Anomaly (950 to 1250 CE, MCA), a period which coincided with glacier retreat. Here, we present a new moraine chronology based on 36Cl surface exposure dating from Lyngmarksbræen glacier, West Greenland. Consistent with other glaciers in the western Arctic, Lyngmarksbræen glacier experienced several advances during the last millennium, the first one at the end of the MCA, in ~1200 CE, was of similar amplitude to two other advances during the LIA. In the absence of any significant changes in accumulation records from South Greenland ice cores, we attribute this expansion to multi-decadal summer cooling likely driven by volcanic and/or solar forcing, and associated regional sea-ice feedbacks. Such regional multi-decadal cold conditions at the end of the MCA are neither resolved in temperature reconstructions from other parts of the Northern Hemisphere, nor captured in last millennium climate simulations.

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          Timing and climate forcing of volcanic eruptions for the past 2,500 years.

          Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.
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            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 degrees 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.
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              Abrupt onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks

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                Author and article information

                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group
                2045-2322
                09 September 2016
                2016
                : 6
                : 32984
                Affiliations
                [1 ]Université Paris 1 Pantheon-Sorbonne, CNRS Laboratoire de Géographie Physique , 92195 Meudon, France
                [2 ]School of Natural Sciences and Psychology, Liverpool John Moores University , Liverpool L3 3AF, UK
                [3 ]Univ. Grenoble Alpes, LGGE , F-38041 Grenoble, CNRS, France
                [4 ]LGGE , F-38041 Grenoble, France
                [5 ]LSCE/IPSL, UMR 8212 (CEA-CNRS-UVSQ), Université Paris Saclay, CEA Saclay , Gif-sur-Yvette 91191, France
                [6 ]EPOC, Universite Bordeaux 1, Allée Geoffroy Saint-Hilaire , Pessac 33615, France
                [7 ]Aix-Marseille Université, CEREGE CNRS-IRD UMR 34, Collège de France , 13545 Aix-en-Provence, France
                [8 ]School of Science and the Environment, Manchester Metropolitan University , Manchester M1 5GD, UK
                Author notes
                [*]

                A comprehensive list of consortium members appears at the end of the paper.

                Article
                srep32984
                10.1038/srep32984
                5016737
                27609585
                ae518ac5-7e2d-4ebb-aeb7-d78623bd36da
                Copyright © 2016, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 01 March 2016
                : 17 August 2016
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