Well, heat energy is considered a form of pollution only in some
contexts. Heat energy is just the energy of molecules jiggling around
(it has kinetic and potential components). Heat energy and pollution
are associated in many ways but only in some cases does the heat energy
"cause" the pollution.
Heat energy itself, when released into the environment in a system
which is not equipped to handle it, is called "thermal pollution".
Examples of this are the use of rivers and lakes to take up extra heat
generated by industrial processes. Factories and electric power plants
are often located by rivers and lakes so they can pump cold water in
and release hot water back. The river or lake is then made warmer, and
this can result in distress to plants and animals living in the rivers
and lakes -- the balance of fish, algae, bacteria, and other organisms
may be upset by the change in temperature.
The production of heat energy usually involves burning fuels, and
this process creates pollution in various forms, depending on which
fuels are used and how they are burned. Burning wood makes smoke,
burning gasoline makes carbon and nitrogen oxides (and other
compounds). Burning coal makes these and often sulfur oxides as well.
Nuclear power plants generate heat for production of electricity, and
they also produce wastes. Animals make heat energy and also wastes. The
use of animal waste as fertilizer means that the definition of
"pollution" also depends on context. Some animal waste very definitely
qualifies as pollution.
Generation of heat energy by solar, wind, and hydroelectric means
generates quite a lot less pollution (although the initial construction
of the equipment may involve generating some pollution). Your toaster
converts electrical energy into heat energy with practically no
pollution, but the generation of the electrical energy in the first
place probably involved some pollution somewhere.
(republished on 07/27/06)