Arctic Sea Ice in the First Half of the 20th Century: Temperature-Based Spatiotemporal Reconstruction
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ic Sea Ice in the First Half of the 20th Century: Temperature-Based Spatiotemporal Reconstruction V. A. Semenova, b, * and T. A. Matveevab aA.M.
Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, 119017 Russia bInstitute of Geography, Russian Academy of Sciences, Moscow, 119017 Russia *e-mail: [email protected] Received May 7, 2020; revised May 14, 2020; accepted June 3, 2020
Abstract—Global warming in the recent decades has been accompanied by a rapid decline of the Arctic sea ice area (SIA) in summer (11% per decade). To understand the reasons for such changes, it is necessary to evaluate the range of long-term variability of the Arctic sea ice in the period before a significant increase of anthropogenic emissions of greenhouse gases into the atmosphere. Current empirical data on the spatiotemporal dynamics of Arctic sea ice until the 1950s have significant gaps. In this study, monthly average gridded sea-ice concentration (SIC) fields in the first half of the 20th century are reconstructed using the relationship between the spatiotemporal patterns of SIC variability and surface air temperature over the Northern Hemisphere. The reconstructed data show a significant negative anomaly of the Arctic SIA (about 1.5 million km2 in September and 0.7 million km2 in March) in the mid-20th century, which is considerably larger than the corresponding anomaly in other gridded SIC datasets. Keywords: Arctic sea ice, mid-20th century warming, Arctic climate DOI: 10.1134/S0001433820050102
INTRODUCTION The decline in Arctic sea-ice area (SIA) in the recent decades seems to be the most spectacular and the most precisely observed manifestation of global current climate changes. Continuous satellite observations since 1978 have made it possible to reconstruct sea ice concentrations (SIC) from passive-microwave measurements [1]. According to these data, the Arctic SIA over the past 40 years of observations has decreased in September, the month of a seasonal Arctic SIA minimum, by 2.57 million km2, or by 41%. The reduction is much slower in winter, and in March, the month of a seasonal Arctic SIA maximum, it is 0.69 million km2 (4.8%). Moreover, the SIA in winter decreases primarily in the Barents Sea and in the Sea of Okhotsk, where only over the past 20 years has it reduced by 34% and 14%, respectively [2]. Such changes strongly enhance heat fluxes to the atmosphere and rearrange the regional and large-scale atmospheric circulation, particularly inducing weather anomalies across Russia [2]. The current decrease of Arctic SIA in paleoreconstructions [3] is unprecedented for the past 1000 years. Before the era of routine satellite observations, the Arctic SIA was monitored using coastal, ship, or aircraft observations and drifting buoys. Such observations allowed the creation of the gridded Arctic SIC data set starting from 1953 [4]. These data have been further augmented by satellite data to form a basis of
all up-to-date gridded SIC data sets used for climatechange analysis (including the reports of
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