Agriculture Reference
In-Depth Information
land transition (Stage I) means that methods
to eliminate, or at least strongly mitigate,
soil carbon loss is a critical challenge to be
addressed as marginal lands are brought
into production. The key synergies are: (i)
gaining local benefits by increasing the in-
come potential from agriculture while miti-
gating external costs to the environment (re-
duced water quality, loss of biodiversity,
soil erosion); and (ii) contributing to the glo-
bal benefits of meeting the growing demand
for food and avoiding further losses of car-
bon to the atmosphere. In some cases, these
synergies will include carbon sequestration
to mitigate climate change (Box 3.2).
Although it would certainly help to
gain influence with relevant policy makers
if quantitative targets for ecosystem func-
tions could be formulated on the basis of
thresholds (Chapter 29, this volume), at this
stage there is probably not sufficient science
evidence to define such thresholds beyond
specific case studies and locations. Plate 4
sketches an outline of how thresholds rela-
tive to the carbon levels under native vege-
tation, supposedly aligned with climate and
soil properties, might differ between func-
tions (cf. Chapter 2, this volume). Local ex-
pertise and expert opinion will be needed to
estimate threshold values, as formal science
cannot yet be brought to this level of synthe-
sis in the face of existing variation.
For a number of special soil types, the
quantities of soil carbon that can be released
to or sequestered from the atmosphere are of
the magnitude (or beyond in the case of peat)
of changes in aboveground carbon stock in
forests. Global carbon mitigation efforts and
their potential financial incentives are likely
to focus on these areas where measurement
and monitoring costs might be justified by
the types of changes in carbon stock that are
feasible. For the 80% of soils outside of
these special categories, economic incentives
Critical thresholds?
At the local level, some measure of carbon
stock over time is needed in order to track
progress along the transition curve. A min-
imum level of carbon is critical for soils to be
able to deliver multiple benefits ( Table 3.1 ) .
Minimum carbon threshold values have been
established at the local level; for example, for
semi-arid Pampas arable lands (Box 3.3). The
question is whether such a measure could
also be identified for the global level.
Box 3.2. Increasing biofuels and food
The potential for land management to harness carbon storage in the soil for climate change mitiga-
tion, while supporting increased biofuel production to partially replace fossil fuels, has been explored
through scenario analysis using computational simulation (Reilly et al ., 2013). The results suggest that
specific policy approaches can help to maintain global warming within a 2°C limit during the coming
decades - a target that is considered to keep warming within safe planetary limits (Rockström et al .,
2009; UNEP, 2011b). The policy scenario allows biofuel production to compete with food production
within a carbon market that provides incentives to store carbon in the soil and in vegetation and offset
CO 2 emissions from oil and gas. One result projected by this specific policy scenario simulation is to re-
duce marginally the share of land supporting food production, with the consequence of increasing food
prices. The scenario analysis assumed a 1% year - 1 increase in land productivity.
The thought experiment presented in the text above indicates that even if the yield gap can be
closed through improved agricultural technology and land management, there may well be additional
requirements for the conversion of marginal lands into agricultural production, with special reference
to more populous parts of the globe to feed more people. The potential competition of land within a
highly valued biofuel market, as illustrated by the experiment of Reilly et al . (2013), presents a further
constraint on food production. The co-benefits of maintaining and enhancing soil organic matter content
during the conversion of marginal lands for either food or biofuel production are likely to be significant.
In addition to mitigating soil carbon loss as greenhouse gas emissions during land conversion, the
co-benefits can contribute to closing the yield gap and to reducing external environmental costs by pro-
tecting water quality and biodiversity and minimizing soil erosion.
 
 
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