15.3.3 Projected changes in the oceans

A new study (Zhang and Walsh, 2006) based on the IPCC AR4 model simulations, projected mean reductions of annually averaged sea ice area in the Arctic by 2080-2100 of 31%, 33% and 22% under the A2, A1B and B1 scenarios, respectively (see Figure 15.3). A consistent model result is that the sea-ice loss is greater in summer than in winter, so that the area of seasonal (winter-only) sea-ice coverage actually increases in many models. The loss of summer sea ice will change the moisture supply to northern coastal regions and will be likely to impact the calving rates of glaciers that are now surrounded by sea ice for much of the year. There will also be increases in wind-driven transport and mixing of ocean waters in regions of sea-ice loss.

The projected increases of Arctic river discharge and precipitation over polar oceans, as well as the projections of increasing discharge from the Greenland ice sheet (Lemke et al., 2007), point to a freshening of the ocean surface in northern high latitudes. However, the projected changes of ice discharge (calving rates) are generally not available from the model simulations, since the ice sheet discharge is not explicitly included in coupled global models.