When humans or natural forces release chemicals or other substances into the environment, the process is known as emission.

Emissions often cause pollution.  Air pollution, for example, is caused when chemicals are released into the air.  However, because natural sources as well as humans cause pollution, it is difficult to define that term exactly.

Many natural processes cause emissions.  When a volcano erupts, it lets out acid, ash, and many toxic gases.  When fires break out in forests, they release smoke, soot, carcinogenic hydrocarbons, dioxins, and carbon dioxide.

Of course, human processes generate tremendous emissions as well.  Driving a car, operating a factory, or using a fireplace all cause emissions to be put out into the air.

It would be unfair to say that all pollution comes from human beings, because nature itself produces much of it.

As a result, some people think it is either unfair or not worthwhile to restrict human pollution production.  These people argue that there will be large natural emissions anyway.

It is important to discover how much pollution nature can handle.  If restricting human pollution will reduce aggregate pollution to a level at which favorable results occur, it may be desirable to restrict pollution.  However, if many of the bad effects of pollution are going to occur anyway, then perhaps pollution should not be restricted as much.