Pollution is an increase of incidence in the environment of substances considered undesireable, when brought about through the activity of mankind. A similar increase, when it occurs through causes not influenced by mankind, is not considered to be pollution.
There are a number of different types of pollution including air pollution, water pollution[?], light pollution and noise pollution.
Although carbon dioxide is not toxic -- and actually stimulates plant growth -- environmentalists labeled carbon dioxide a "pollutant" in the 1990s, because they believe that carbon dioxide emissions will lead to harmful global warming (see greenhouse gas, global warming hypothesis).
See also: petroleum, renewable energy.
