| Summary: | The early 20 th ;century warming (ETCW) in the northern;high latitudes;was comparable in magnitude to modern warming, yet occurred at a time when the increase in;atmospheric greenhouse gases;was;several times less;than in recent decades. Understanding the nature of the ETCW is the key to determine the relative contribution of internal variability and external natural and anthropogenic impacts to global and regional climate change.The discrepancy between the observed and simulated by CMIP models temperature variations in the Arctic in the mid-20 th ;century indicates the important role of internal climate variability in the Northern Extratropics.;In the current study a multiple linear regression method is used as a statistical tool to analyze the functional relationships between ETCW and atmospheric and oceanic internal variability indices. The contribution of the NAO, AO, PNA, AMO and PDO indices of natural variability to climate changes in the Arctic region during the 20 th ;century is assessed using observations and reanalyses.The results of the statistical analysis supports the concept of the major role of the North Atlantic sea surface temperatures variability in the Arctic climate change in the mid-20 th ;century period.
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