Environmental Engineering Reference
In-Depth Information
3.3 Anthropogenic Sources of Atmospheric GHGs
Anthropogenic sources are primarily responsible for the greenhouse gases (GHGs)
inputs to the atmosphere. CO
2
is mostly produced anthropogenically from the
burning of fossil fuels and plant litter and from oil flaring, cement manufactur-
ing and other industrial activities (IPCC
2007a
; Sabine et al.
2004
; Smith
2004
;
Archer
2005
; Canadell et al.
2007
; Hofmann et al.
2009
; Subak et al.
1993
;
Marland and Rotty
1984
; Crutzen and Andreae
1990
; Keeling et al.
1996
). It has
recently been shown that the annual emissions because of fossil fuel burning have
grown by about 80 %, from 21 to 38 gigatonnes (Gt), between 1970 and 2004. The
rate of growth of CO
2
-eq emissions was much higher during the more recent dec-
ade 1995-2004 (0.92 GtCO
2
-eq per year) than during the previous period 1970-
1994 (0.43 GtCO
2
-eq per year) (IPCC
2007a
). CH
4
is produced from fossil fuel
production and consumption including oil and gas field activities, coal mining,
plant litter/wood processing, domestic sewage treatment, enteric fermentation and
other biomass burning (Mosier et al.
2004
; Smith
2004
; Kreileman and Bouwman
1994
; IPCC
2001
; Subak et al.
1993
; Crutzen
1991
; Flessa et al.
2002
). The major
sources of anthropogenic aerosols are sulfur-containing fossil fuels, biomass burn-
ing and explosive volcanic eruptions (IPCC
2001
,
2007a
).
3.4 Deforestation
Deforestation or changes in land-surface cover can significantly affect atmospheric
CO
2
, CH
4
and N
2
O (IPCC
2001
,
2007a
; Kreileman and Bouwman
1994
; van der
Werf et al.
2009
; Raich and Schlesinger
1992
; Subak et al.
1993
; Bouwman
1990
;
Crutzen and Andreae
1990
; Keller et al.
1986
; Sitch et al.
2005
; Detwiler and Hall
1988
; Myers
1989
; Houghton
1991
). The above-cited processes can contribute
in three ways to global warming: First, deforestation i.e. the decline of terrestrial
plants can significantly reduce the uptake of CO
2
from the atmosphere by photo-
synthesis, which is vital for plants growth. Such a phenomenon would thus give
indirect contribution to the increase of atmospheric CO
2
. Second, deforestation
can reduce evaporation and increases surface temperature. Third, changes in land-
surface cover can enhance the degradation of soil DOM and OM by both photoin-
duced and microbial processes, thus uncovered land surfaces can release GHGs
directly to atmosphere (Schiettecatte et al.
2006
,
2007
; Borges et al.
2008
; Omar
et al.
2010
; Brandt et al.
2009
; Rutledge et al.
2010
; Thomas et al.
2004
,
2005
,
2007
; Raich and Schlesinger
1992
; Xie et al.
2004
). Soil respiration rates are very
high in the first year after the clear-cutting of plants, apparently due to the higher
soil temperatures and to the decomposition of the debris that the soil incorporated
during the deforestation (Raich and Schlesinger
1992
). Deforestation is the second
largest anthropogenic source of CO
2
to the atmosphere after fossil fuel burning. It
accounted for 17.3 % of anthropogenic GHGs in the 2004 total emissions to the
