This article is from the Fusion FAQ, by Robert F. Heeter firstname.lastname@example.org with numerous contributions by others.
Fusion, like fission, creates no greenhouse gases, no smog,
and no acid rain. The major source of "air pollution" from
fusion would be, well, helium, which is completely inert and
is already a significant constituent of the earth's atmosphere.
Fusion isn't chemical energy, so it doesn't create chemical
byproducts that would cause air pollution.
Fusion consumes less fuel mass per unit of energy produced
than any other fuel-consuming energy source. There is also
far more fusion fuel than for any other fuel-consuming
energy source. Fusion gives you the most energy "bang
for your buck" and therefore minimizes the environmental
burdens of searching for and producing energy.
Fusion fuel is also much more widely distributed, since
all likely fuel elements are found abundantly in seawater.
There would be no Persian Gulf-type wars over access to
fusion fuel. Given the destructive nature of wars, this
is good for the environment as well as good for people.
With fusion, you don't need to rip up the ground like
coal mines do, or worry about oil spills, or devote
miles and miles of land to wind or solar farms. Fusion creates
more energy with less resource investment than any other
form of energy known to man.