Increasing population density, urbanization, industrialization and other development schemes, are exerting ever increasing pressure on the carrying capacity of land and resources, leading in particular to a rapid rate of deforestation, expanding desertification in some countries, and the near extinction of some wildlife species. Physical factors such as earthquakes, hurricanes, monsoon rains and the immense problem of poverty in some countries accelerate the decline in environmental resources.
Throughout most of history, the interactions between human development and the environment have been relatively simple and localized. The complexity and scale of these interactions are now increasing, especially as resources became scarcer and competition for them increases. What were once local pollution incidents shared throughout a common watershed or air basin now involve several, or many, nations, as in the case of acid precipitation. Acute episodes of relatively reversible damage now affect multiple generations, as in the case of the disposal of radioactive wastes. Straightforward questions of ecological preservation versus economic growth how involve complex linkages, as in the case of the interaction between energy and crop production, deforestation and climate change.
The most important ways in which human activity is interfering with the global ecosystem are: (a) fossil fuel burning which may double the atmospheric carbon dioxide concentration by the middle of the next century, as well as further increasing the emissions of sulphur and nitrogen very significantly; (b) expanding agriculture and forestry and the associated use of fertilizers (nitrogen and phosphorous) are significantly altering the natural circulation of these nutrients; (c) increased exploitation of the fresh water system both for irrigation in agriculture and industry and for waste disposal.
According to present understanding the most important impacts of these changes in the long-term are: (a) a gradual change towards a warmer climate of which very little is known; (b) a decrease in the concentration of ozone in the stratosphere, due to the increased release of nitric oxides and chlorine compounds and increase in the troposphere, due to increased release of hydrocarbons and nitrate compounds; (c) an increase of the areas affected by lake and stream acidification in mid-latitudes and possibly also in the tropics, associated with the possibility of significant disturbance in the ion balance of soils (as is now being found in the case of aluminium); (d) a decrease of the extend of tropical forests, which will enhance the rate of increase in atmospheric carbon dioxide concentration and release other minor constituents to the atmosphere, which may also contribute to soil degradation; (e) due to loss of organic matter and nutrients, soil deterioration will occur and this implies a reduced possibility for the vegetation to return to pristine conditions; (f) a trend toward the eutrophication of estuarine and coastal marine areas; (g) more frequent development of anoxic conditions in freshwater and marine systems and sediments.
Asia is the world's most polluted and environmentally degraded region and is facing serious environmental challenges. The region has only 30 per cent of the world's land area and supports 60 per cent of the world population. This is leading to land degradation, especially in marginal areas, and habitat fragmentation. High population densities are putting enormous stress on the environment. Continued rapid economic growth and industrialization is likely to cause further environmental damage, with the region becoming more degraded, less forested, more polluted and less ecologically diverse in the future. Habitat fragmentation has depleted the wide variety of forest products that used to be an important source of food, medicine and income for indigenous people. Forest fires caused extensive damage in 1997-98. Asia has lost half its forest cover in the short space of 30 years, and with it countless unique animal and plant species, causing the spread of deserts, erosion, silting of rivers, flooding and crop losses. A third of its agricultural land is degraded, and its rivers and lakes are among the world's most contaminated. Fish stocks have also fallen by half. No other area had as many heavily polluted cities. The WHO found that of the 15 cities with the worst air pollution, 13 were in Asia. Widespread coal burning in China and India are a major source of sulfur and nitrogen contamination.
The impact (I) of any group or nation on the environment is represented qualitatively by the relation I = PAT where P is the size of the population, A is the per capita affluence, measured by per capita rate of consumption, and T is a measure of the damage done by the technologies that are used in supplying the consumption (Hardin's Third Law of Human Ecology, attributed to Ehrlich and Holdren).
The suggestion may be made that the Third Law is too conservative. The Third Law suggests that I varies as p to the power n where n = 1. There are situations where the impact of humans increases more rapidly than linearly with the size of the population P so that n is greater 1.