One of the shared concerns of all types of environmentalism is opposing pollution. In this sense, most people in the world are "environmentalists" since hardly anyone wants to breathe air choked with fumes or swim in dirty water. For people in underdeveloped countries, the problem is often finding clean drinking water.
In another sense, the meaning of the term "pollution" has been extended to include industrial emission of carbon dioxide, which is beneficial to plant growth and harmless to human beings in ordinary concentrations. Proponents of the global warming hypothesis and supporters of the Kyoto Protocol classify carbon dioxide as a "pollutant" due to their belief that it contributes to harmful global warming (see climate change issues).
In psychology, environmentalism is the theory that environment (in the general and social sense) plays a greater role than heredity in determining an individual's development.
The term in both senses was first used in the early 20th century. They are related by the observation that if one's surroundings play a great role in individual development, and those surroundings are either green, beautiful, healthy and thriving, or gray, ugly, degraded, unhealthy and unable to sustain themselves, two different attitudes to life develop. This is reflected in the modern controversy over measuring well-being which often places importance on aesthetics and experience of a healthy natural environment, e.g. gardens.
As human population and industrial activity have increased, the growth of (political, nature-promoting) environmentalism reflects considerable controversy, with those who place high importance on environmentalism (environmentalists) coming into conflict with those who accord it lesser importance or who otherwise disagree with various elements of the environmentalist's current agenda.
Environmentalists can conserve resources in many ways. Driving a fuel-efficient car, taking short showers, and eating vegan food are among these. Fuel-efficient cars have lower emissions and consume less oil, which is a limited resource. Short showers consume less fresh water. Vegan food (soybeans, rice, green vegetables) takes less land, water, and oil to grow and eat directly than to grow soybeans, feed the soybeans to a pig, and then eat the pig.
Environmentalists often clash with others over issues of the management of natural resources, e.g. the atmosphere as a "carbon dump", the focus of climate change and global warming controversy. They usually seek to protect commonly owned, or unowned, resources for future generations.
Those who take issue with new untested technologies are more precisely known, especially in Europe, as political ecologists. They usually seek, in contrast, to preserve the integrity of existing ecologies and ecoregions, and in general are more pessimistic about human 'management'.
Various extreme ideologies of radical environmentalism, and several ecology-based theories of anarchy (known as (small-g) green anarchism) are often cited to justify equipment sabotage, logging or fishing blockades, and even burning of houses impinging on a natural ecology. Environmentalists differ in their views of these ideologies and groups, but almost all condemn violent actions that can harm humans. They are somewhat more tolerant of the destruction of property not essential to sustaining or saving human life. The most extreme, sometimes called terrists, often claim to view themselves as part of nature, simply acting to protect itself from man.
Environmentalism in fiction
See also