The annual maximum sea ice extent typically occurs in March. In March 2008, the maximum ice extent was 15.2 million km2. This marked a second year of slight recovery in winter ice extent from the record minimum of 14.4 million km2 for the period 1979–2008, which was observed in 2006. For comparison, the mean monthly ice extent for March and September, for the period 1979–2008, is 15.6 and 6.7 million km2, respectively.

The Arctic sea ice cover is composed of perennial ice (the ice that survives year-round) and seasonal ice (the ice that melts during the summer). Consistent with the diminishing trends in the extent and thickness of the cover is a significant loss of the older, thicker perennial ice in the Arctic. Data from the NASA QuikSCAT launched in 1999 (Nghiem et al., 2007) and a buoy-based Drift-Age Model (Rigor and Wallace, 2004) indicate that the amount of perennial ice in the March ice cover has decreased from approximately 5.5 to 3.0 million km2 over the period 1958–2007. While there is considerable interannual variability, an overall downward trend in the amount of perennial ice began in the early 1970s. This trend appears to coincide with a general increase in the Arctic-wide, annually averaged surface air temperature, which also begins around 1970. In recent years, the rate of reduction in the amount of older, thicker perennial ice has been increasing, and now very little ice older than 5 years remains (Maslanik et al. 2007).

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