Agriculture Reference
In-Depth Information
to the climate change debate. The only op-
tion to achieve permanence is in the con-
tinuity and integrity of national accounts
and international commitments and ac-
countability - the track record of the latter is
not very good, with the failure of the UN-
FCCC parties to agree on full implementa-
tion and a seamless sequel to the Kyoto
Agreement (2008-2012).
Peatland soils as hotspots
of soil C emissions
Peat soils store more than half of the
world's soil carbon on less than 10% of
the area, and land conversion on peat con-
tributes a disproportionately large fraction
of total soil-based emissions (van Noord-
wijk
et al
., 2014). Peat soils, however, are
more frequent in cool and subarctic cli-
mates, and in the tropics the equivalence
of peat and mineral soils in terms of car-
bon stock is only true in the South-east
Asia region, with Indonesia and Malaysia
holding about 80% of global tropical peat-
land carbon. The high fluxes due to land
use and land-use change on peat are asso-
ciated with high uncertainty; a recent effort
to establish emission factors for tropical
peatlands in the IPCC has failed to reach
consensus. Peatlands are hotspots of con-
flict over access rights as well (Galudra
et al
., 2011).
Land-use change as part
of total anthropogenic emissions
In terms of quantity, the current changes in
terrestrial C stocks are dwarfed by fossil fuel
emissions of CO
2
. Historically, anthropo-
genic land cover change is estimated to
have released
156
petagrams (Pg) of C to
the atmosphere in the period 1850-2000,
equivalent to 57% of fossil fuel emissions over
the period (DeFries
et al
., 1999; Houghton,
2003). Despite shifts in geographic focus
('hotspots'), the net terrestrial C emissions
have not changed much between the 1960s
and now, at about 1.1 Pg C year
-
1
;
in the
1960s, this represented about 30% of total
anthropogenic emissions, in the 1990s, 18%
and in 2010, 9% of the total, due to the large
increase of fossil fuel emission (Canadell
et al
., 2007; Le Quéré
et al
., 2009; Peters
et al
., 2012).
Changing above- plus belowground
terrestrial C stocks from a net source to be-
come a net sink of atmospheric CO
2
is an
essential element of strategies to keep glo-
bal temperature rise below the +2°C thresh-
old, which is considered a boundary of the
safe planetary operating space (Rockström
et al
., 2009), alongside shifts in energy use.
Estimates of emissions from soil due to
land-use change are, however, lacking or
highly uncertain, while subnational and
project-based emission reduction efforts
face substantive measurement costs if they
want to include soil C in the consider-
ations at required precision levels; costs of
measurement that are generally not justi-
fied by the economic compensation for en-
hanced C storage (Cacho
et al
., 2008),
except for the special cases where high
emission rates can be avoided.
Erosion and sedimentation
as fractal dimension
The net contribution of belowground car-
bon losses to the total of terrestrial C losses
is uncertain, as part of the on-site loss
measured in agricultural lands has been
due to erosion and lateral transport fol-
lowed by deposition elsewhere in the
landscape, rather than direct release to the
atmosphere (Paustian
et al
., 1997). Due to
the lateral flow interactions, the net loss of
soil + organic matter from any area has a
fractal dimension, with deposition taking
a larger and larger share of the plot-level
erosion values, the larger the area con-
sidered (van Noordwijk
et al
., 1998a; Ver-
bist
et al
., 2010). Incorporating the fate of
deposited materials, van Oost
et al
. (2012)
concluded that historical erosion in the
landscape they studied had been at least
neutral in terms of atmospheric CO
2
emis-
sions. These insights are yet to become
mainstream in accounting, as critical data
for deposition sites are not normally col-
lected.
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