Climate Change Mitigation - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 120

Full participation of the agricultural sector in GHG mitigation still faces some challenges and bar-
riers related to measurement, monitoring and reporting requirements in C offset markets. Further im-
provements are needed in methodologies and approaches that would help project designers and policy
makers to integrate significant mitigation effects in agriculture development projects.

Introduction and Background

in 2005, 68% for Benin in 2000, 81% for
Ethiopia in 1995 and even 91% for Chad in
1993) (UNFCCC, 2012). For all Annex I
countries together, the agricultural sector
(excluding LUCF) contributes about 9% of
total emissions.
This huge uncertainty applies also to
soil C sinks at national and regional levels.
In most cases, there is no agreement on the
regional net contribution of SOC from agri-
cultural soils. For instance, in Europe, some
authors reported a recent net sink (Ciais et al .,
2011a), whereas others reported net emis-
sions (Bellamy et al ., 2005; Ceschia et al .,
2010). Most regions have even less available
information (e.g. Africa; see Ciais et al ., 2011b)
and thus uncertainties are large and it is dif-
ficult to draw clear conclusions.
Agricultural activities are also directly or
indirectly responsible for the largest part of
the emissions, due to deforestation worldwide
(Hosonuma et al ., 2012). Collectively, agricul-
ture, forestry and other land use (AFOLU) is
recognized to contribute about one-third of
global anthropogenic emissions (Baumert et al .,
2005; IPCC, 2007), and thus agriculture should
be strongly considered in policies and actions
concerning GHG mitigation.
Although the AFOLU sector is a GHG
source, it can also act as a sink for CO 2 ,
through improved land use and management
practices. Smith et al . (2007) estimated that
the global potential for all mitigation options
in agriculture, considering all gases and ex-
cluding fossil fuel replacement from bio-
energy, were c .5500-6000 Tg CO 2 -eq year − 1
by 2030, with an associated 95% confidence
interval from 3000 to 8700 Tg CO 2 -eq year − 1 .
Moreover, the authors also estimated that
about 90% of total mitigation potential was
from soil carbon sequestration (SCS) includ-
ing cropland and grassland management and
the restoration of organic cultivated soil and
degraded land. As with emissions, the miti-
gation potential and measures vary among
regions; however, developing countries, which

At global level, agriculture and forestry are
major contributors to increased greenhouse
gas (GHG) concentrations, from emissions of
nitrous oxide (N 2 O), methane (CH 4 ) and car-
bon dioxide (CO 2 ). Agricultural emissions of
N 2 O and CH 4 amount to c .10-12% of total glo-
bal anthropogenic emissions of GHGs (IPCC,
2007), with emissions in 2005 estimated at
3.3 Pg CO 2 -equivalent for CH 4 and 2.8 Pg
CO 2 -equivalent for N 2 O. Soil represents the
main C stock in agricultural systems, and de-
creases or increases of soil organic C (SOC)
stocks, due to changes in land use and man-
agement, climate or other drivers, result in net
emissions or removals of CO 2 . Global esti-
mates for the net CO 2 contribution from agri-
cultural soils are difficult to quantify and
have large uncertainty, but recent IPCC (2007)
estimates are for a net emission of 40 Tg CO 2 -
eq year − 1 . This relatively small net contribu-
tion is in contrast to a much larger historical
loss of C from soils, and also potential losses
induced by global warming, which could be
in the order of several Pg CO 2 year - 1 (Amund-
son, 2001). In a recent study, Shevliakova
et al . (2009) estimated a net annual terrestrial
carbon source due to all land-use activities
ranging from 1.1 to 1.3 Pg C during the 1990s.
Those authors also estimated separately, but
with higher uncertainties, the contributions
from grasslands (ranging from an emission of
0.37 Pg C year − 1 to a sink of 0.15 Pg C year −1 )
and for croplands (net emissions in the range
0.6-0.9 Pg C year −1 ).
In any case, the contribution of agricul-
ture to GHG emissions varies from country
to country, depending mainly on the struc-
ture of the economy. Excluding land-use
change and forestry (LUCF), agricultural
emissions vary from a few per cent (e.g. 1%
for Jordan in 2000, 6% for the USA, 10% for
the 27 members of the European Union in
2010, 14% for China in 1994) to one-half or
more of total emissions (e.g. 48% for Brazil