The Global Challenge for Soil Carbon - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 2

This ' 4 × 40' challenge for global soils is
to meet the anticipated demands of human-
ity (Godfray et al ., 2010) to:
1. Double the food supply worldwide;
2. Double the fuel supply, including renew-
able biomass;
3. Increase by more than 50% the supply of
clean water, all while acting to
4. Mitigate and adapt to climate change and
biodiversity decline regionally and world-
wide.

The build-up of organic matter and car-
bon is one of the key factors in the develop-
ment of ecosystem functions as soil forms
and evolves. Thus, carbon loss is one of the
most important contributions to soil degrad-
ation. Furthermore, this central role of carbon
across the range of soil functions establishes
a buffer function for soil organic matter
whereby loss of soil carbon results in a de-
cline in the soil functions, and maintaining
or enhancing soil carbon confers resilience to
these under pressure from environmental
changes (van Noordwijk et al ., Chapter 3, this
volume). In the ensuing chapters of this vol-
ume, significant detail is provided to illus-
trate and quantify the uniquely central role of
soil carbon in the delivery of ecosystem ser-
vices and the opportunity that this presents
in managing soil and land use positively to
enhance the multiple benefits that soil car-
bon provides. Set against these opportunities
to reverse, conserve and even enhance soil
functions is the operational cost implied in
the proactive management of soil carbon.
The global soil resource is already
showing signs of serious degradation from
human use and management. Soil degrad-
ation has escalated in the past 200 years
with the expansion of cultivated land and
urban dwelling, along with an increasing
human population. Degradation continues,
with soil and soil carbon being lost through
water and wind erosion, land conversion
that is associated with accelerated emis-
sions of greenhouse gases and the burning
of organic matter for fuel or other purposes.
Significant degradation has taken place
since the industrial revolution; recent and
ongoing degradation is substantial; bulk soil
loss from erosion remains severe in many
locations, with the accompanying loss of
soil functions; and the release of carbon and
nitrogen from soil as the greenhouse gases
CO 2 , CH 4 and N 2 O continues to contribute to
global warming ( Table 1.1 ) .
The capacity of soils to deliver ecosystem
goods and services which lead to human bene-
fits, and the degree to which these benefits are
lost due to soil degradation, varies signifi-
cantly with geographical location (Plate 1).
The global results in Plate 1 provide a first

The demographic drivers of environ-
mental change and the demand for biomass
production are already putting unprecedented
pressure on Earth's soils (Banwart, 2011).
Dramatic intensification of agricultural pro-
duction is central among proposed meas-
ures to potentially double the global food
supply by 2050. An urgent priority for ac-
tion is to ensure that soils will cope world-
wide with these multiple and increasing de-
mands (Victoria et al ., 2012).
Soils have many different essential
life-supporting functions, of which growing
biomass for food, fuel and fibre is but one
(Blum, 1993; European Commission, 2006;
Victoria et al ., 2012). Soils store carbon
from the atmosphere as a way to mediate at-
mospheric greenhouse gas levels; they filter
contaminants from infiltrating recharge to
deliver clean drinking water to aquifers;
they provide habitat and maintain a micro-
bial community and gene pool that decom-
poses and recycles dead organic matter and
transforms nutrients into available forms for
plants; they release mineral nutrients from
parent rock; and they store and transmit
water in ways that help prevent floods. These
functions underpin many of the goods and
services that can lead to social, economic
and environmental benefit to humankind.
Specific land uses can create trade-offs by
focusing on the delivery of one or a few of
these functions at the expense of others.
Under the pressures of increasingly inten-
sive land use, when decisions are made on
land and soil management, it is essential to
protect and to enhance the full range of the
essential life-sustaining benefits that soils
provide.