Environmental costs arise either through the damage done as a consequence of resource exploitation or through the effort expended to redress the damage. Damage costs may also be imposed in the process of development, through the destruction of certain types of renewable resources such as: large-scale loss of tropical forests, soil degradation due to salinization, and imperfect cultivation of sub-marginal lands.
Some 30 million square kilometres (19% of the earth's land surface) are threatened with desertification, and consequently with huge economic and human losses. From 1970-1980, the economic cost of pollution damage in developed countries varied between 3 and 5% of GNP.