Despite growing awareness and increasing investments in environmental protection, pressures on the world’s natural resources and ecosystems continue to increase rapidly. Theimpacts of human activities reach into every corner of the natural world. For instance, between one third and one half of the Earth’s land surface has been substantially transformed by agriculture, urbanization, and commercial activities of various kinds; about one quarter of all bird species have been driven to extinction; and more than one half of all accessible surface water, as well as an enormous quantity of groundwater, is diverted for human uses. These uses have brought unquestionable benefits to human welfare. But the upshot of this growing human domination of the planet is that no ecosystem on Earth is free from pervasive human influence.
This section considers some of the more widespread and pressing threats to the planet’s physical and biological resources. Global forest cover, for example, faces enormous pressure in both tropical and temperate regions from conversion to agricultural and urban uses, as well as from logging. Deforestation rates in many developing countries continue to increase, even as the condition of many forests in developed countries is degraded by air pollution. Risks to the world’s rich array of living species are also climbing. These threats to biodiversity are particularly intense in aquatic systems such as coral reefs and freshwater habitats in rivers, lakes, and wetlands. Bioinvasions from exotic species introduced accidentally through global trade and tourism or by deliberate import for agriculture comprise a kind of “biological pollution” that also poses a growing threat to the world’s biodiversity, both aquatic and terrestrial.
Other resources face critical depletion in the near future. In the absence of strict management schemes to reduce fishing pressure, many marine fish stocks continue to decline, endangering an important source of food and employment. Meanwhile, water availability is set to become one of the prime constraints on development in many regions in the near future. This section also reports on recent efforts to put a price tag on the services that natural ecosystems such as forests and wetlands supply the world without charge. This preliminary effort to assign economic values to these essential services is a powerful way to demonstrate the costs of continuing to degrade the world’s vital systems.