Land-use/land-cover changes

Estimates of the Earth's landscape which have been disturbed from their natural state vary according to how the disturbance is defined. In terms of global cultivated land, Dudal (1987) indicates that 14.6 × 106 km2 of a potential cultivated coverage of 30.31 × 106 km2 are presently being utilized. Since the Earth's land surface covers 133.92 × 106 km2, this indicates that 10.9% of the landscape is cultivated, with the potential level reaching 22.6% coverage.

This value of land disturbance due to human activities is an underestimate, however. Brasseur et al. (2005) report that up to half of the Earth's landscape has been directly altered. Human activities also include domestic grazing of semi-arid regions, urbanization, drainage of wetlands, and alterations in species composition due to the introduction of exotic trees and grasses. In the United States, for example, 426 000km2 (4.2% of the total land area) have been artificially drained (Richards, 1986).

In China, of the 2 × 106 km2 in the temperate arid and semi-arid grassland regions, hundreds of thousands of square kilometers have been degraded due to overgrazing and the overextension of agriculture, often to the extent that desertification has occurred (Committee on Scholarly Communication with the People's Republic of China, 1992).

The influence of vegetation on climate includes its influence on albedo, waterholding capacity of the soil, stomatal resistance to water vapor transfer, aerodynamic roughness of the surface, and effect on snow cover.