Observations of snow-covered area for the Northern Hemisphere show a significant development in the later 20th century, with a reduction of the area covered by snow in the spring (March-April) from some 38 million km2 in the 1930-ies to todays 35 million km2. Snow represents an important resource for water, ecosystems and human activities, as well as for reflecting incoming sun light. The linear trend shows a decrease in snow-covered area of 2.7 ± 1.5 _ 106 km2 or 7.5 ± 3.5 %. The shaded fields in the figure represents the 5 to 95% range of the data.
From collection: Global Outlook for Ice and Snow
Hugo Ahlenius, UNEP/GRID-Arendal