11.8 Polar Regions

Assessment of projected climate change for the polar regions:

The Arctic is very likely to warm during this century in most areas, and the annual mean warming is very likely to exceed the global mean warming. Warming is projected to be largest in winter and smallest in summer.

Annual arctic precipitation is very likely to increase. It is very likely that the relative precipitation increase will be largest in the winter and smallest in summer.

Arctic sea ice is very likely to decrease in extent and thickness. It is uncertain how the Arctic Ocean circulation will change.

It is likely that the Antarctic will be warmer and that precipitation will increase over the continent.

It is uncertain to what extent the frequency of extreme temperature and precipitation events will change in the polar regions.

Polar climate involves large natural variability on interannual, decadal and longer time scales, which is an important source of uncertainty. The projections of the trends in the underlying teleconnections, such as the Northern Annular Mode (NAM) or ENSO, contain substantial uncertainty (see Chapter 10). Further, understanding of the polar climate system is still incomplete due to its complex atmosphere-land-cryosphere-ocean-ecosystem interactions involving a variety of distinctive feedbacks. Processes that are not particularly well represented in the models are clouds, planetary boundary layer processes and sea ice. Additionally, the resolution of global models is still not adequate to resolve important processes in the polar seas. All this contributes to a rather large range of present-day and future simulations, which may reduce confidence in the future projections. A serious problem is the lack of observations against which to assess models, and for developing process knowledge, particularly over Antarctica.