There has been decrease in Northern Hemisphere spring snow cover since 1950, retreat of glaciers globally since the 1990s, decrease in Arctic Sea ice extent between 1979–1988 and 2010–2019 and surface melting of the Greenland Ice Sheet over the past two decades. The observed decrease in the Arctic Sea ice extent is about 40% in September and about 10% in March. However, no significant trend has been observed in the Antarctic Sea ice extent from 1979 to 2020 due to regionally opposing trends and large internal variability.