CLIMATE MODELS simulate the interactions between the atmosphere, and the ocean and land surface beneath it. The land properties that matter most to the atmosphere include land elevation; the the presence of mountains, for example, can strongly affect the flow of air, causing it to rise and fall, thus creating zones of high and low rainfall.

The albedo of the land, which determines how much of the incident sunlight is reflected, depends critically on the nature of the ground cover, whether it is snow, ice, sand, or vegetation. The moisture content of the soil has a strong effect on the hydrologi-cal cycle, for example, the amount of evaporation into the atmosphere, and the amount of run-off into rivers and lakes. The roughness of the land surface ...