For the Northern Hemisphere (primarily the Arctic), observations using remote sensing technologies have been used to measure the extent and the to assess the development. Despite considerable year-to-year variability, significant negative trends are apparent in both maximum and minimum ice extents, with a rate of decrease of 2.5 per cent per decade for March and 8.9 per cent per decade for September (linear least squares regression). The differences in extent are calculated as anomalies compared to the 1979-2000 average, which was 7.0 million sqkm2 in September, and 15 million sqkm2 in March. Please note that this graphic has been updated with the 2007 figures.
From collection: Global Outlook for Ice and Snow
Hugo Ahlenius, UNEP/GRID-Arendal