Environmental Engineering Reference
In-Depth Information
Fig. 1.13
Predicted
increases in nitrogen
(N) and phosphorus (P)
fertilizers, irrigated
land, pesticide use and
global areas under
crops and pasture by
2020 (dark bars) and
2050 (light bars). (From
Laurance, 2001, based
on data in Tilman et al.,
2001a.)
150
100
50
0
Agricultural variable
Fig. 1.14
The concen-
tration of atmospheric
CO
2
measured at the
Mauna Loa Observa-
tory, Hawaii showing
the seasonal cycle
(peaking each northern
summer when
photosynthetic rates are
maximal in the
Northern Hemisphere)
and, more signifi cantly,
the long-term increase
that is due largely to
the burning of fossil
fuels. (Courtesy of the
Climate Monitoring and
Diagnostics Laboratory
(CMDL) of t he National
Oceanic and Atmos-
pheric Administration
(NOAA).)
380
360
340
320
1960
1970
1980
1990
2000
2006
Year
in sea level, and large changes to global patterns of precipitation, winds, ocean cur-
rents and the timing and scale of storm events.
The principal cause of increased greenhouse gases has been the combustion of
fossil fuels, but other factors also come into play. Adding the carbon dioxide released
when limestone is kilned to produce cement (about 0.1 Pg of carbon per year) to
fossil fuel use (5.6 Pg per year), a net increase of 5.7 (
0.5) Pg C per year was added
to the atmosphere during the period 1980-1995 (1 petagram
±
10
15
g) (Houghton,
2000). Landuse change is believed to have pumped a further 1.9 (
=
0.2) Pg C into the
atmosphere each year. In particular, the exploitation of tropical forest causes a sig-
nifi cant release of carbon dioxide, particularly if the forest is cleared and burnt to
make way for agriculture. Much of the carbon goes up in smoke, followed by further
carbon dioxide release as vast stores of soil organic matter decompose.
Where does the extra 7.6 Pg C per year of carbon end up? The observed increase
in atmospheric carbon dioxide accounts for 3.2 (
±
±
1.0) Pg C (i.e. 42% of the human
inputs), while much of the rest, 2.1 (
0.6) Pg C, dissolves in the oceans. This leaves
2.3 Pg C per year, which is generally attributed to a terrestrial 'sink' - probably
±
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