Environmental Engineering Reference
In-Depth Information
greenhouse gases that humankind has added to the atmos-
phere as of the year
. Carbon dioxide has a removal
time of more than
years. However, only about two-thirds come out in one
removal time. The elapse of each removal time reduces
the amount remaining by roughly two-thirds of what was
there at the start of the period.
Carbon dioxide in the atmosphere has increased by
about
years, perhaps as long as
% since the start of the industrial age. Today it
is nearly
parts per million (ppm), compared with
ppm in the eighteenth century. Sometimes you will
see mention of something called carbon dioxide equiva-
lent (CO
e). This is the amount of CO
that would mimic
the effect of all of the greenhouse gases taken together.
Today
'
sCO
e is about
ppm. (
Technical Note
.
discusses the sources of the other greenhouse gases.)
.
The Global Carbon Cycle
The global carbon cycle as sketched in
Figure
tracks
where all the carbon comes from and where it goes. The
ocean is the largest CO
reservoir, holding about
.
gigatonnes. (A gigatonne
is the inter-
national term for one billion metric tonnes. Each metric
tonne is
-
abbreviated Gt
-
kilograms or about
pounds.) Next is
the land at about
Gt. The smallest of the reservoirs
is the atmosphere with about
Gt. The land and the
oceans take carbon out of the atmosphere with one mech-
anism and put it back into the atmosphere with another.
Global carbon emissions into the atmosphere in the
year
Gt per year, but only half of that
stays there and becomes the main concern for the
were about
