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V I E W P O I N T
Soil Carbon Sequestration Impacts on Global
Climate Change and Food Security
R. Lal
The carbon sink capacity of the world’s agricultural and degraded soils is 50 to
66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil
organic carbon sequestration with adoption of recommended technologies de-
pends on soil texture and structure, rainfall, temperature, farming system, and
soil management. Strategies to increase the soil carbon pool include soil resto-
ration and woodland regeneration, no-till farming, cover crops, nutrient manage-
ment, manuring and sludge application, improved grazing, water conservation
and harvesting, efficient irrigation, agroforestry practices, and growing energy
crops on spare lands. An increase of 1 ton of soil carbon pool of degraded
cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha)
for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as
enhancing food security, carbon sequestration has the potential to offset fossil-
fuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global
fossil-fuel emissions.
The global soil carbon (C) pool of 2500
gigatons (Gt) includes about 1550 Gt of
soil organic carbon (SOC) and 950 Gt of
soil inorganic carbon (SIC). The soil C pool
is 3.3 times the size of the atmospheric pool
(760 Gt) and 4.5 times the
size of the biotic pool (560
Gt, fig. S1). The SOC pool
to 1-m depth ranges from
30 tons/ha in arid climates
to 800 tons/ha in organic
soils in cold regions, and a
predominant range of 50
to 150 tons/ha. The SOC
pool represents a dynamic
equilibrium of gains and
losses (Fig. 1). Conversion
of natural to agricultural
ecosystems causes deple-
tion of the SOC pool by as
much as 60% in soils of
temperate
regions
and
75% or more in cultivated
soils of the tropics. The
depletion is exacerbated
when the output of C ex-
ceeds the input and when
soil degradation is severe.
Some soils have lost as
much as 20 to 80 tons
C/ha, mostly emitted into the atmosphere.
Severe depletion of the SOC pool degrades
soil quality, reduces biomass productivity,
and adversely impacts water quality, and
the depletion may be exacerbated by pro-
jected global warming.
Terrestrial ecosystems contributed to at-
mospheric CO
2
enrichment during both the
preindustrial and industrial eras (Table 1).
During the preindustrial era, the total C
emission from terrestrial ecosystems was
supposedly about twice (320 Gt or 0.04 Gt
C/year for 7800 years) that of the industrial
era (160 Gt or 0.8 Gt C/year for 200 years)
(
1
). Between 1850 and 1998, the emission
from fossil-fuel combustion (270
⫾
30 Gt)
was about twice that from the terrestrial
ecosystems (136
⫾
55 Gt) (
2
). The latter
includes 78
⫾
12 Gt from soil, of which
about one-third is attributed to soil degra-
dation and accelerated erosion and two-
thirds to mineralization (Table 1). The es-
timates of historic SOC loss range widely,
from 44 to 537 Gt, with a common range of
55 to 78 Gt (
3
).
Soil Carbon Sequestration
Carbon sequestration implies transferring
atmospheric CO
2
into long-lived pools and
storing it securely so it is not immediately
reemitted. Thus, soil C sequestration means
increasing SOC and SIC stocks through
judicious land use and recommended man-
agement practices (RMPs). The potential
soil C sink capacity of managed ecosystems
approximately equals the cumulative his-
toric C loss estimated at 55 to 78 Gt. The
attainable soil C sink capacity is only 50 to
66% of the potential capacity. The strategy
of soil C sequestration is cost-effective and
environmentally friendly (table S1).
The rate of increase in
the SOC stock, through
land-use
change
and
adoption of RMPs, fol-
lows a sigmoid curve, at-
tains the maximum 5 to
20 years after adoption
of RMPs, and continues
until SOC attains another
equilibrium.
Observed
rates of SOC sequestra-
tion in agricultural and
restored ecosystems de-
pend on soil texture, pro-
file characteristics, and
climate, and range from
0 to 150 kg C/ha per year
in dry and warm regions
(
4
), and 100 to 1000 kg
C/ha per year in humid
and cool climates (
5
–
8
)
(fig. S2). With continu-
ous use of RMPs, these
rates can be sustained for
20 to 50 years or until the
soil sink capacity is filled (
8
,
9
). The SOC
sequestration is caused by those manage-
ment systems that add high amounts of
biomass to the soil, cause minimal soil
disturbance, conserve soil and water, im-
prove soil structure, enhance activity and
species
diversity
of
soil
fauna,
and
strengthen mechanisms of elemental cy-
cling (Fig. 2, table S2). Common RMPs
that lead to SOC sequestration are mulch
Carbon Management and Sequestration Center, The
Ohio State University Columbus, OH 43210, USA.
E-mail: lal.1@osu.edu
SOC
Pool
1550 Pg
Humification
Particle
detach-
ment
Oxidation
Trans-
location
CO
2
CO
2
CO
2
CO
2
CO
2
CO
2
(2-20% of
the C added)
Leaching
of DOC
0.4-0.6 Gt
0.8-1.2 Gt
Deposition
in aquatic
ecosystems
and burial in
depressional sites
Redistribution
over the
landscape
C added in
above-
ground
residues,
and root
biomass
Aquatic systems
Erosion
Fig. 1.
Processes affecting soil organic carbon (SOC) dynamics. Arrows pointed upward
indicate emissions of CO
2
into the atmosphere. There may also be emission of CH
4
under anaerobic conditions, although most well-drained soils are a sink of CH
4
. DOC,
dissolved organic carbon.
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farming, conservation tillage, agroforestry
and diverse cropping systems, cover crops
(Fig. 3), and integrated nutrient manage-
ment, including the use of manure, com-
post, biosolids, improved grazing, and
forest management. The potential of SOC
sequestration also lies in restoration of de-
graded soils and ecosystems (
10
) whose
resilience capacity is intact. The rate of SIC
sequestration as secondary carbonates is
low (5 to 150 kg C/ha per year) and is
accentuated by biogenic processes and
leaching of carbonates into the ground-
water (
11
,
12
), especially in soils irrigated
with water containing low carbonates.
Soil Carbon Sequestration for
Mitigating Climate Change
Estimates of the total potential of C seques-
tration in world soils vary widely from a
low of 0.4 to 0.6 Gt C/year (
9
) to a high
of 0.6 to 1.2 Gt C/year (
13
). Thus, the
potential is finite in capacity and time.
Nonetheless, soil C sequestration buys us
time until the alternatives to fossil fuel take
effect. Some issues related to this strategy
are as follows:
1) Agricultural chemicals. Most RMPs
involve C-based input. It takes 0.86 kg
C/kg N, 0.17 kg C/kg P
2
O
5
, 0.12 kg C/kg
K
2
O, 0.36 kg C/kg lime, 4.7 kg C/kg of
herbicides, 5.2 kg C/kg of fungicides, 4.9
kg C/kg of insecticides (
14
), and 150 kg
C/ha for pumping groundwater for irriga-
tion (
15
). Tillage operations emit 15 kg
C/ha for moldboard plowing, 8 kg C/ha for
chisel plowing and heavy tandem disking, 6
kg C/ha for light tandem disking, 11 kg
C/ha for subsoiling, 4 kg C/ha for cultiva-
tion, and 2 kg/ha for rotary hoeing (
16
).
Therefore, conversion from
conventional till to no-till
farming reduces emission by
30 to 35 kg C/ha per season
(
16
). Similarly, a judicious
use of C-based inputs is es-
sential to enhancing use ef-
ficiency and minimizing
losses. However, inputs are
needed not for soil C seques-
tration per se, but for increas-
ing food production and en-
suring sustainable use of soil
and water resources.
2) Nutrients required. Car-
bon is only one of the ele-
mental constituents of humus.
It is estimated that sequestra-
tion of 1 Gt of C in world
soils would require 80 mil-
lion tons (Mt) of N, 20 Mt of
P, and 15 Mt of K. In com-
parison, the global fertilizer
use in 2000 was 136 Mt (
17
).
However, there are several
sources of nutrients for C se-
questration, including biolog-
ical nitrogen fixation, recy-
cling
from
subsoil,
aerial
deposition, use of biosolids,
and crop residues. One ton of
cereal residue contains 12 to
20 kg N, 1 to 4 kg P, 7 to 30
kg K, 4 to 8 kg Ca, and 2 to 4
kg Mg. Annually, 3 Gt of res-
idues of grain crops are pro-
duced globally (table S3),
which if recycled rather than
removed for fuel and other
uses,
would
improve
soil
quality and sequester C. Crop
residue is also a potential
source of energy by direct
combustion, or for production
of ethanol or H
2
. It can be
used either for biofuel production or to
sequester C and improve soil quality. The
economics of these two competing uses
need to be assessed.
3) Soil erosion and deposition. The SOC
is preferentially removed by wind- and
water-borne sediments through erosional
processes. Some of the SOC-enriched sed-
iments are redistributed over the landscape,
others are deposited in depressional sites,
and some are carried into the aquatic eco-
systems (Fig. 1). Although a part of the C
translocated by erosion may be buried and
redistributed (
18
), the rest is emitted into
the atmosphere either as CO
2
by mineral-
ization or as CH
4
by methanogenesis.
Erosion-induced deposition and burial may
be 0.4 to 0.6 Gt C/year compared with
perhaps 0.8 to 1.2 Gt C/year emitted into
the atmosphere (Fig. 1) (
19
). Quantification
Cropland Soils: 1350 Mha
[0.4 to 0.8 Gt C/yr]
Restoration of Degraded and
Desertified Soils: 1.1 billion ha
[0.2 to 0.4 Gt C/yr]
• Conservation tillage (100-1000)
• Cover crops (50-250)
• Manuring and INM (50-150)
• Diverse cropping systems (50-250)
• Mixed farming (50-200)
• Agroforestry (100-200)
Acid savanna soils, 250 Mha in South
America, have a high potential
• Erosion control by water
(100-200)
• Erosion control by wind (50-100)
• Afforestation on marginal lands
(50-300)
• Water conservation/harvesting
(100-200)
3.7 billion ha in semi-arid and sub-
humid regions
• Grazing management (50-150)
• Improved species (50-100)
• Fire management (50-100)
• Nutrient management
*Both SOC and SIC are sequestered
• Using drip/sub-irrigation
• Providing drainage (100-200)
• Controlling salinity (60-200)
• Enhancing water use efficiency/water
conservation (100-200)
*Both SOC and SIC are sequestered
Potential of Carbon
Sequestration in
World Soils
[0.4 - 1.2 Gt C/yr]
Irrigated Soils: 275 Mha
[0.01 to 0.03 Gt C/yr]*
Range Lands and Grass Lands:
[0.01 to 0.3 Gt C/yr?]*
Fig. 2.
Ecosystems with a high and attainable soil C sequestration potential are cropland, grazing/range land,
degraded/desertified lands, and irrigated soils. Forest soils are included under afforestation of agriculturally
marginal and otherwise degraded/desertified soils. Reforestation of previously forested sites have small additional
soil C sequestration. The potential of C sequestration of range lands/grassland is not included in the global total
because part of it is covered under other ecosystems, and there are large uncertainties. Rates of C sequestration
given in parentheses are in kg C/ha per year, are not additive, and are low under on-farm conditions. [Rates are
cited from (
2
–
9
,
15
,
25
,
37
–
39
) and other references cited in the supporting material.]
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of emission versus burial of C is a high
priority. Yet, an effective soil erosion con-
trol is essential to sustainable use of agri-
cultural soils and improving environment
quality.
4) Extractive farming practices. The an-
nual depletion rate of nutrients for sub-
Saharan Africa (SSA) caused by low-input/
subsistence farming is estimated to be 40 kg
of NPK/ha of cultivated land since the mid-
1960s (
20
). Mining SOC from soil for nutri-
ents through organic-matter decomposition
has an effect on the atmosphere similar to that
of fossil-fuel combustion. Therefore, RMPs
must enhance rather than deplete SOC pool
and soil fertility, increase rather than main-
tain or decrease crop yield per unit use of
fertilizer and other inputs, and improve rather
than degrade soil quality.
5) Societal value and hidden benefits.
Commodification of soil C is important for
trading C credits. Carbon trading markets
have existed since 2002, especially in Euro-
pean Union countries (
21
). The low current
price ($1/ton CO
2
) of SOC may increase with
emission cap and regulation. For the concept
of SOC credits trading to become routine as
a part of the solution to mitigate climate
change, the ability to measure short-term (3-
to 5-year) changes in SOC pool exists (
22
),
but the price of soil C must be based on both
on-site and off-site societal benefits (table
S4). Undervaluing soil C can lead to a
“tragedy of the commons.”
6) Hydrologic and carbon cycles. Because
renewable freshwater is scarce, a projected
increase in cereal production by 56% be-
tween 1997 and 2050 (
23
) must occur on the
same or smaller land area and with the same
or less water. Thus, linking the hydrologic
and C cycles through conser-
vation of water resources is
crucial to improving agronom-
ic yields and to soil C seques-
tration in dryland. The low
SOC stock in rainfed agriculture
can be enhanced through water
conservation, water harvesting,
and water-efficient farming sys-
tems. Enhancing SOC stock in
dryland ecosystems through no-
till farming is important to
drought management: a truly
win-win option (
24
).
7) Soil C sequestration and
global warming. Global warm-
ing is a “century-scale” prob-
lem and a “global commons”
issue. Soil C sequestration is a
related but separate issue with
its own merits of increasing
productivity, improving water
quality, and restoring degraded
soils and ecosystems, irrespec-
tive of the global-warming
debate. Offsetting fossil-fuel emissions by
achievable SOC potential provides multiple
biophysical and societal benefits (table S3).
Furthermore, soil C sequestration is a bridge
across three global issues— climate change,
desertification, and biodiversity—and a natural
link among three UN conventions.
8) Other greenhouse gases. Enhancing
SOC stock increases the soil’s capacity to
oxidize CH
4
, especially under no-till farm-
ing (
25
), but may also exacerbate emission
of N
2
O (
26
). Fluxes of CH
4
and N
2
O may
change the CO
2
-mitigation potential of soil
management practices and must be consid-
ered along with SOC sequestration.
9) Soils of the tropics. Because of its
severe depletion and degradation, the C
sink capacity of soils of the tropics may be
high, but the rate of sequestration can be
low. The need for enhancing soil quality is
also more urgent in soils of the tropics than
in soils of high latitudes because of low
crop yields. Yet, the challenge is greater
because of weak institutions, limited infra-
structure, and predominantly resource-poor
agriculture systems. Soil-restorative farm
policies must be implemented to mitigate
soil-degradative trends.
10) Permanence. Soil C sequestration is
a natural, cost-effective, and environment-
friendly process. Once sequestered, C re-
mains in the soil as long as restorative land
use, no-till farming, and other RMPs are
followed. Soil sink capacity and perma-
nence are related to clay content and min-
eralogy, structural stability, landscape po-
sition, moisture and temperature regimes,
and ability to form and retain stable micro-
aggregates.
Soil Carbon Sequestration and Global
Food Security
Global hotspots of soil degradation with a
high priority for soil restoration and C se-
questration include SSA, central and south
Asia, China, the Andean region, the Carib-
bean, and the acid savannas of South Amer-
ica. Complete residue removal for fodder
and fuel is a norm in south Asia and Africa.
Thus, depletion of SOC stock from the root
zone has adversely affected the soil produc-
tivity and environmental quality of these
regions. Simply put, poor farmers have
passed on their suffering to the land
through extractive practices. They cultivate
Fig. 3.
Important recommended management practices are no-till farming, cover crops, manuring and
agroforestry. (
A
) Long-term no-till plots were established at the International Institute of Tropical Agriculture,
Ibadan, in 1971 and continued through 1987. The adoption of no-till by small landholders in Africa and
Asia has been constrained by removal of crop residue mulch for fodder and fuel, nonavailability of a proper
seed drill that can cut through the residue, and prohibitively expensive herbicides. (
B
) Agroforestry,
sowing wheat under the canopy of poplar, is widely practiced in Punjab, India. Other combinations of trees
and crops and forages may be beneficial to sustainable use of soil-water resources and C sequestration in
site-specific situations.
Table 1.
Estimates of pre- and postindustrial
losses of carbon from soil and emission from
fossil-fuel combustion. Data were compiled
from diverse sources (
1
–
3
). Ruddiman (
1
)
estimated the emission from land-use con-
version during the postindustrial era at 0.8
Gt C/year for 200 years at 160 Gt C.
Source
Historic carbon
emission (Gt)
Preindustrial era
Fossil-fuel
combustion
0
Land-use
conversion at
0.04 Gt C/year
for 7800 years
320
Postindustrial era
Fossil-fuel
combustion
(since 1850)
270
⫾
30
Land-use conversion
136
⫾
5
Soil cultivation
78
⫾
12
Erosion
26
⫾
9
Mineralization
52
⫾
8
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marginal soils with margin-
al inputs, produce marginal
yields, and perpetuate mar-
ginal living and poverty.
As a source of nutrients for
growing crops, the SOC
pool is a mean of produc-
tion in subsistence farming
systems of SSA, which ac-
counts for only 2.5% of the
fertilizer consumption and
2% of the world’s irrigated
land area, both essential to
SOC sequestration. Bene-
fits of RMPs cannot be re-
alized in severely degraded
soils depleted of their SOC
stock—soil’s life support
system. An optimum level
of SOC stock is needed to
hold water and nutrients,
decrease risks of erosion
and degradation, improve
soil structure and tilth, and
provide energy to soil mi-
croorganisms. The SOC is
a biomembrane that filters
pollutants,
reduces
sedi-
ment load in rivers, de-
creases hypoxia in coastal
ecosystems, degrades con-
taminants, and is a major
sink for atmospheric CO
2
and CH
4
. Fertilizer applica-
tion is an important strate-
gy of increasing crop yield
in SSA (
27
), but its effec-
tiveness is enhanced when used in conjunc-
tion with crop residue mulch (
28
) or trees
(
20
). Increase in SOC stock increases crop
yield even in high-input commercial agri-
culture (
29
), but especially in soils where it
has been depleted (
30
). An increase of 1 ton
of SOC increased wheat grain yield by 27
kg/ha in North Dakota, United States (
29
),
and by 40 kg/ha in semi-arid pampas of
Argentina (
31
), 6 kg/ha of wheat and 3
kg/ha of maize in alluvial soils of northern
India (
32
), 17 kg/ha of maize in Thailand
(
33
), and 10 kg/ha of maize and 1 kg/ha of
cowpea in western Nigeria (
34
). High SOC
stock is also needed to maintain consistent
yields through improvements in water and
nutrient holding capacity, soil structure,
and biotic activity. The critical limit of
SOC concentration for most soils of the
tropics is 1.1% (
35
). Increasing SOC con-
centration from a low of 0.1 to 0.2% to a
critical level of 1.1% is a major challenge
for tropical ecosystems. Yet, a drastic re-
duction in the SOC pool in SSA and else-
where must be reversed in order to advance
food security. An 18-year experiment in
Kenya showed that the yield of maize and
beans was 1.4 tons/ha per year without
external input and 6.0 tons/ha per year
when stover was retained and fertilizer and
manure were applied. The corresponding
SOC stocks to 15-cm depth were 23.6 tons/
ha and 28.7 tons/ha, respectively (
36
). This
is the type of quantum jump in crop yields
needed at the continental scale to ensure
food security in SSA. The vicious cycle of
declining
productivity– depleting
SOC
stock–lower yields will have to be broken
(Fig. 4) by improving soil quality through
SOC sequestration in order to free much of
humanity from perpetual poverty, malnutri-
tion, hunger, and substandard living.
Conclusions
Soil C sequestration is a strategy to achieve
food security through improvement in soil
quality. It is a by-product of the inevitable
necessity of adopting RMPs for enhancing
crop yields on a global scale. While reduc-
ing the rate of enrichment of atmospheric
concentration of CO
2
, soil C sequestration
improves and sustains biomass/agronomic
productivity. It has the potential to offset
fossil-fuel emissions by 0.4 to 1.2 Gt C/year,
or 5 to 15% of the global emissions.
Soil organic carbon is an extremely valua-
ble natural resource. Irrespec-
tive of the climate debate, the
SOC stock must be restored,
enhanced, and improved. A
C-management policy that in-
cludes regulation-based trad-
ing soil C must be developed.
Likewise, a widespread adop-
tion of RMPs by resource-
poor farmers of the tropics is
urgently warranted. The soil
C sequestration potential of
this win-win strategy is finite
and realizable over a short
period of 20 to 50 years. Yet,
the close link between soil C
sequestration and world food
security on the one hand and
climate change on the other
can neither be overempha-
sized nor ignored.
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Soil
degradation
and
nutrient
depletion
Decline in
environmental
quality (emission
of CO
2
& other
gases, hypoxia,
siltation of
reservoirs)
Depletion of soil
organic matter
Decline in
agronomic and
biomass
productivity
Food
insecurity,
malnutrition,
and
hunger
Fig. 4.
Cereal yields in Africa have been stagnant since early 1970s and stand
at a meager 1 ton/ha. The vicious cycle of deletion in soil organic matter–
decline in crop yield–food insecurity–soil and environmental degradation can be
broken by improving soil fertility through enhancement of the soil organic
matter pool, which requires use of sustainable agricultural technologies for
water and nutrients management, including no-till farming, composts and
mulching, leguminous cover crops, water harvesting, agroforestry, and integrat-
ed farming systems, along with judicious use of chemicals. This strategy can
break the tyranny of hunger.
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University, Columbus, OH.
Supporting Online Material
www.sciencemag.org/cgi/content/full/304/5677/1623/DC1
SOM Text
Figs. S1 to S3
Tables S1 to S4
References
V I E W P O I N T
Breaking the Sod: Humankind, History, and Soil
J. R. McNeill
1
* andVerena Winiwarter
2,3
For most of history, few things have mattered more to human communities than
their relations with soil, because soil provided most of their food and nutrients.
Accordingly, some of the earliest written documents were agricultural manuals
intended to organize, preserve, and impart soil knowledge. Indeed, ancient civiliza-
tions often worshipped the soil as the foundry of life itself. For the past century or
two, nothing has mattered more for soils than their relations with human commu-
nities, because human action inadvertently ratcheted up rates of soil erosion and,
both intentionally and unintentionally, rerouted nutrient flows.
Our distant ancestors found their food by
hunting and foraging. They depended indi-
rectly on soils to support plant growth, but
they did not much alter soils by their ac-
tions, except where they routinely burned
vegetation. With the transitions to agricul-
ture (which probably happened indepen-
dently at least seven times, beginning about
10,000 years ago), human dependence
upon, and impact upon, soils became more
direct and more obvious. Neolithic farmers,
in southwest Asia and elsewhere, depleted
soils of their nutrients by cultivating fields
repeatedly, but they simultaneously en-
riched their soils once they learned to keep
cattle, sheep, and goats, pasture them on
nonarable land, and collect them (or merely
their dung) upon croplands. They also wor-
shipped deities that they connected not only
to fertility in livestock and women, but also
to soil productivity.
When a population lived amid the fields
that sustained them, the net transfer of nu-
trients into or out of the fields remained
minor, as after shorter or longer stays in
human alimentary canals and tissues, nutri-
ents returned to the soils whence they had
come. Urban life changed that, systemati-
cally drawing nutrients from fields to cities,
from whence wastes left via streams or
rivers, en route to the sea. So civilization,
with its systemic links between cities and
hinterlands, over the past 5000 years has
posed an ongoing challenge for farmers
trying to maintain soil fertility.
Soil Erosion
In most settings, agriculture promoted soil
erosion, although to highly varying de-
grees. On a global scale, soil erosion oc-
curred in three main waves. The first arose
as a consequence of the expansion of
early river-basin civilizations, mainly in
the second millennium B.C.E. Farmers
left the valleys and alluvial soils of the
Yellow River, Indus, Tigris-Euphrates, and
lesser rivers (or from the Maya lowlands)
and ascended forested slopes, where they
exposed virgin soils to seasonal rains. The
loess plateau of north China, for example, began
to erode more quickly during this period, earning
the Yellow River its name (
1
). Over the next
3000 years, farmers in Eurasia, Africa, and the
Americas gradually converted a modest
proportion of the world’s forests into farmland
or pasture and thereby increased rates of soil
erosion, but the fertile soils of the world’s grass-
lands were little affected.
That changed in the 16th to 19th centuries
when, in a second great wave of soil erosion,
stronger and sharper plowshares helped break
the sod of the Eurasian steppe, the North Amer-
ican prairies, and the South American pampas.
The exodus of Europeans to the Americas,
Australia, New Zealand, Siberia, South Africa,
Algeria, and elsewhere brought new lands un-
1
Edmund A. Walsh School of Foreign Service, Inter-
cultural Center 600, Box 571035, Georgetown Uni-
versity, 3700 O Street, N.W., Washington, DC
20057–1035, USA.
2
Institute for Soil Research, Uni-
versity of Natural Resources and Applied Life Sci-
ences, A-1-80, Vienna, Austria.
3
Institute for Inter-
disciplinary Studies, A-1070, Vienna, Austria.
*To whom correspondence should be addressed. E-
mail: mcneillj@georgetown.edu
Fig. 1.
A16th-century Italian fresco of a cultivated field.
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Soil Carbon Sequestration Impacts on Global Climate Change and Food Security
R. Lal
Science 304 (5677), . DOI: 10.1126/science.1097396
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