Cryosphere and climate

This chapter will discuss two main issues related to the cryosphere and climate. One is the effect of sea ice and salinity gradients on ocean circulation, and in particular the possible role of sea ice transport on the ocean conveyer belt. The other is the effect of the cryosphere on climate, and in particular in high-latitude warming under increased CO2. In understanding the role of the cryosphere in both cases, it is useful to elucidate two types of toy sea ice models. Neither of these represents reality, but both are useful for illustrating the archetypal features of sea ice that control much of its large-scale behavior. The first model is a simple slab thermodynamic sea ice model as presented by Thorndike. In this model there are no dynamical effects and the thickness of ice is determined by surface heat budget and oceanic heat flux considerations, with the thickness of the ice critically affecting the effective conductivity whereby heat is transferred from the bottom ice boundary to the upper ice boundary. In this model all of the sea ice characteristics are controlled by the vertical heat fluxes from the atmosphere and ocean into the ice. The thickness is controlled by the ice's becoming an effective insulator as it thickens, thus reducing conductive heat loss to the atmosphere. A second model emphasizes the effects of dynamics. It considers the ice pack to be a collection of floes moving in response to synoptic wind fields and ocean currents. These motions create semipermanent leads (open areas) over which ice can grow rapidly.