Factors of natural climate variability contributing to the Early 20th Century Warming in the Arctic

The Early 20th century warming (ETCW) in the Northern Polar region was comparable by its average pace to the modern warming, but the mechanism of this climate anomaly remains a matter of debate. The key issue is to assess the contribution of internal variability and external natural and human impacts. Internal variability is one of the most likely mechanisms that may explain a large part of ETCW. This paper provides an overview of the existing mechanisms of internal climate variability responsible for the long-term climate anomaly in the mid-twentieth century.