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Climate Variability in the Subarctic Area for the Last 2 Millennia

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Climate Variability in the Subarctic Area for the Last 2 Millennia Climate variability in the subarctic area for the last 2 millennia Marie Nicolle, Maxime Debret, Nicolas Massei, Christophe Colin, Anne Devernal, Dmitry Divine, Johannes Werner, Anne Hormes, Atte Korhola, Hans Linderholm To cite this version: Marie Nicolle, Maxime Debret, Nicolas Massei, Christophe Colin, Anne Devernal, et al.. Climate variability in the subarctic area for the last 2 millennia. Climate of the Past, European Geosciences Union (EGU), 2018, 14 (1), pp.101-116. 10.5194/cp-14-101-2018. hal-01715912 HAL Id: hal-01715912 https://hal.archives-ouvertes.fr/hal-01715912 Submitted on 23 Feb 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Clim. Past, 14, 101–116, 2018 https://doi.org/10.5194/cp-14-101-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 3.0 License. Climate variability in the subarctic area for the last 2 millennia Marie Nicolle1, Maxime Debret1, Nicolas Massei1, Christophe Colin2, Anne deVernal3, Dmitry Divine4,5, Johannes P. Werner6, Anne Hormes7, Atte Korhola8, and Hans W. Linderholm9 1Normandie Univ, UNIROUEN, UNICAEN, CNRS, M2C, 76000 Rouen, France 2GEOPS, CNRS, University of Paris-Sud, 91405 Orsay CEDEX, France 3Centre de recherche en géochimie et géodynamique (Geotop), Université du Québec à Montréal, Montréal, QC, Canada 4Norwegian Polar Institute, Tromsø, Norway 5Department of Mathematics and Statistics, Arctic University of Norway, Tromsø, Norway 6Bjerknes Center for Climate Research and Department of Earth Science, University of Bergen, Bergen, Norway 7University of Gothenburg, Department of Earth Sciences, Gothenburg, Sweden 8Department of Environmental Sciences, Environmental Change Research Unit (ECRU), University of Helsinki, P.O. Box 65, 00014 Helsinki, Finland 9Regional Climate Group, Department of Earth Sciences, University of Gothenburg, 40530 Gothenburg, Sweden Correspondence: Marie Nicolle ([email protected]) Received: 10 March 2017 – Discussion started: 31 March 2017 Revised: 12 December 2017 – Accepted: 15 December 2017 – Published: 25 January 2018 Abstract. To put recent climate change in perspective, it is 30-year cycle is found in Alaska and seems to be linked to necessary to extend the instrumental climate records with the Pacific Decadal Oscillation, whereas ∼ 20–30- and ∼ 50– proxy data from paleoclimate archives. Arctic climate vari- 90-year periodicities characterize the North Atlantic climate ability for the last 2 millennia has been investigated using variability, likely in relation with the Atlantic Multidecadal statistical and signal analyses from three regionally aver- Oscillation. These regional features are probably linked to aged records from the North Atlantic, Siberia and Alaska the sea ice cover fluctuations through ice–temperature posi- based on many types of proxy data archived in the Arctic tive feedback. 2k database v1.1.1. In the North Atlantic and Alaska, the ma- jor climatic trend is characterized by long-term cooling inter- rupted by recent warming that started at the beginning of the 1 Introduction 19th century. This cooling is visible in the Siberian region at two sites, warming at the others. The cooling of the Lit- Since the beginning of the industrial era, the global average ◦ tle Ice Age (LIA) was identified from the individual series, temperature has increased by about 1 C and recent decades but it is characterized by wide-range spatial and temporal ex- have been the warmest in the last 1400 years (PAGES 2k pression of climate variability, in contrary to the Medieval Consortium, 2013; IPCC, 2013). The warming is more pro- Climate Anomaly. The LIA started at the earliest by around nounced at high latitudes in the Northern Hemisphere than in AD 1200 and ended at the latest in the middle of the 20th cen- other parts of the Earth (Serreze and Barry, 2011; PAGES 2k tury. The widespread temporal coverage of the LIA did not Consortium, 2013), being more than twice the rate and mag- show regional consistency or particular spatial distribution nitude in the Arctic than the global average (Cohen et al., and did not show a relationship with archive or proxy type 2014). To place this warming in the perspective of long- either. A focus on the last 2 centuries shows a recent warm- term natural climate variability, the instrumental time series ing characterized by a well-marked warming trend parallel are not sufficient and it is necessary to extend the meteo- with increasing greenhouse gas emissions. It also shows a rological measurements back in time with proxy data from multidecadal variability likely due to natural processes acting paleoclimate archives (ice cores, tree rings, lake sediments, on the internal climate system on a regional scale. A ∼ 16– speleothems, marine sediments and historical series). Published by Copernicus Publications on behalf of the European Geosciences Union. 102 M. Nicolle et al.: Climate variability in the subarctic area for the last 2 millennia Over the last decade, extensive efforts have been made In this study, we explore the regional expression of the to collect and compile paleoclimate available data to recon- Arctic–subarctic climate variability during the last 2 millen- struct past climate variability on regional, hemispheric and nia using statistical and wavelet analysis. To do so, we de- global scales. Most temperature reconstructions include dif- fine three regions, North Atlantic, Alaska and Siberia, from ferent types of archives and proxies (Moberg et al., 2005; which we calculated climatic variations. Hence, the regional Mann et al., 2009; Kaufman et al., 2009; Ljungqvist, 2010; mean records allowed us to determine if the timing of the Marcott et al., 2013) and some studies focused on a single long-term and secular (MCA and LIA) climatic fluctuations paleoclimate archive type and/or area (e.g., McGregor et al., that occur on the global Arctic–subarctic scale are also char- 2015, for oceans; Weissbach et al., 2016, for ice core; Wilson acteristic of the regional climate variability. Special attention et al., 2016, for tree rings). In the Arctic and subarctic area is given to the last 2 centuries, with the comparison between (90–60◦ N), several multi-proxy reconstructions of tempera- the three regional mean records and instrumental climate in- tures encompassing the last 2 millennia were published on dex, to determine the influence of internal climate variabil- a global (PAGES 2k Consortium, 2013; McKay and Kauf- ity but also the ability of paleoclimate series to reproduce man, 2014; Werner et al., 2017) and regional scale (Hanhi- decadal to multidecadal variability observed in instrumental järvi et al., 2013). The annual resolution of these reconstruc- data. tions allows the study of the climate variability from low fre- quencies (i.e., millennial and multi-centennial fluctuations) to high frequencies such as decadal variations. 2 Paleoclimate data Climatic reconstructions highlighted a millennial cooling trend associated with the monotonic reduction in summer The records used in this study were compiled by the Arc- insolation at high northern latitudes and a reversal marked tic 2k working group of the Past Global Changes (PAGES) by an important warming of more than 1 ◦C consistent with research program. This working group released a database the increase in greenhouse gases since the mid-20th century comprising 56 proxy records for the Arctic area (ver- (e.g., Kaufman et al., 2009; PAGES 2k Consortium, 2013). sion 1.1.1; McKay and Kaufman, 2014). The database con- The long-term cooling trend correlates with the millennial- tains all available records that meet data quality criteria con- scale summer insolation reduction at high northern latitudes cerning location (from north of 60◦ N), time coverage (ex- (Kaufman et al., 2009) but an increased frequency of vol- tending back to at least AD 1500), mean resolution (better canic events during the last millennium may also have con- than 50 years) and dating control (at least one age control curred with and contributed to the cooling episodes that oc- point every 500 years) (Fig. 1a). See Table S1 in the Supple- curred after AD 1000 (PAGES 2k Consortium, 2013; Sigl et ment for more information about each site (cf. also McKay al., 2015). and Kaufman, 2014). Superimposed on the long-term climate fluctuation, Proxy records are from different archive types. Most continental-scale temperature reconstructions in the North- are continental archives with very reliable chronologies ern Hemisphere highlight major climatic warming and cool- (16 ice cores, 13 tree rings, 19 lake sediment cores and ing pulses during the last millennium, with relatively warm 1 speleothem). Six records are from marine archives and conditions during the Medieval Climate Anomaly (MCA, one is a historic record (months of ice cover). Among the AD 950–1250; Mann et al., 2009) and a cold Little Ice Age 56 records, 35 have an annual resolution (Fig. 1b). Hence, (LIA, AD 1400–1700; Mann et al., 2009) period. The LIA the high temporal resolution of the Arctic 2k database series is, however, characterized by an important spatial and tem- offers the possibility of studying the high-frequency climate poral variability, particularly visible on a more regional scale variability of the last 2 millennia, assuming that the proxy (e.g., PAGES 2k Consortium, 2013). It has been attributed record climate variability and the archiving process do not to a combination of natural external forcings (solar activity induce a bias in the multi-annual to centennial frequencies and large volcanic eruptions) and internal sea ice and ocean analyzed.
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