IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group I: The Physical Science Basis Assessment of Changes in Sea Ice Thickness

Sea ice thickness is one of the most difficult geophysical parameters to measure at large scales and, because of the large variability inherent in the sea-ice-climate system, evaluation of ice thickness trends from the available observational data is difficult. Nevertheless, on the basis of submarine sonar data and interpolation of the average sea ice thickness in the Arctic Basin from a variety of physically based sea ice models, it is very likely that the average sea ice thickness in the central Arctic has decreased by up to 1 m since the late 1980s, and that most of this decrease occurred between the late 1980s and the late 1990s. The steady decrease in the area of the summer minimum arctic sea ice cover since the 1980s, resulting in less-thick multi-year ice at the start of the next growth season, is consistent with this. This recent decrease, however, occurs within the context of longer-term decadal variability, with strong maxima in arctic ice thickness in the mid-1960s and around 1980 and 1990, due to both dynamic and thermodynamic forcing of the ice by circulation changes associated with low-frequency modes of atmospheric variability.

There are insufficient data to draw any conclusions about trends in the thickness of antarctic sea ice.