In order to estimate the impacts of a future climate change it is of course necessary to know many details of that change. All current methods for supplying those details fall short of what is needed, and this deficiency presents a large challenge to the climate science community.
Important interactions take many forms.
The rate at which society emits heat-trapping gases, for example, depends on policy actions at the national and international level, actions likely to be shaped in part by knowledge of possible rates of climate change and the impacts that will follow. The climate and the biosphere are coupled through changes in atmospheric composition, surface color and roughness, evapotranspiration, and other factors. Although most studies focus on one of these systems, an increasing number of investigators now consider one or more interactions among the systems. See also Dickinson, Land Atmosphere Interaction, in this issue. Each step will be reviewed in turn.