FIGURE 4.16 Mean sea-ice thickness for (left) March and (right) September based on ensemble members from six models under A1B emissions scenario. (a and b) Year when the September ice extent reached 4.6 million km² by these models and (c and d) year when the Arctic reached nearly sea-ice conditions (less than 1.0 million km²) in September. Source: Wang and Overland, (2009: Figure 3).

by the end of the 21st century for a global warming of 2-4ºC above late 20th century values or 3-5ºC above pre-industrial values This linear relationship between sea-ice loss and global-averaged surface air temperature has implications for sea-ice recovery. One set of simulations using the A1B scenario suggests that Arctic sea ice may recover if GHG emissions were reduced. This response is linear for the annual sea-ice extent but nonlinear for September (Holland et al., 2006, 2010).

Compared to the Arctic very few studies examine the predicted sea-ice changes for the Antarctic. However, many of the characteristics of projected change are like those for the Arctic. Over the 21st century Antarctic sea-ice