Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 258

ic waters and one in open water off West Antarctica. All three carried highly experienced
polar crews and two were passenger vessels.
Before the 1970s, a large proportion of sea ice centred very roughly over the central
Arctic survived the summer and continued to exist through several summers as multiyear
ice until it was advected (carried by currents) to lower and warmer latitudes within the
Arctic. However, since at least 1979, satellite microwave data and sonar observations from
nuclear submarines show that sea ice thickness has been declining as less and less ice sur-
vives from one year to the next and multiyear ice becomes increasingly less common. In
fact, the amount of circumpolar Arctic multiyear sea ice decreased by 42% between just
2004 and 2008. For the month of March, multiyear ice has decreased from 26% of the ice
cover in 1988 to 19% in 2005 and reached only 7% in 2012. (See Figure 10.7 .)