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The potential of agricultural land management to contribute to lower global surface temperatures

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Removal of atmospheric carbon dioxide (CO2) combined with emission reduction is necessary to keep climate warming below the internationally agreed upon 2°C target. Soil organic carbon sequestration through agricultural management has been proposed as a means to lower atmospheric CO2 concentration, but the magnitude needed to meaningfully lower temperature is unknown. We show that sequestration of 0.68 Pg C year⁻¹ for 85 years could lower global temperature by 0.1°C in 2100 when combined with a low emission trajectory [Representative Concentration Pathway (RCP) 2.6]. This value is potentially achievable using existing agricultural management approaches, without decreasing land area for food production. Existing agricultural mitigation approaches could lower global temperature by up to 0.26°C under RCP 2.6 or as much as 25% of remaining warming to 2°C. This declines to 0.14°C under RCP 8.5. Results were sensitive to assumptions regarding the duration of carbon sequestration rates, which is poorly constrained by data. Results provide a framework for the potential role of agricultural soil organic carbon sequestration in climate change mitigation.
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The potential of agricultural land management to
contribute to lower global surface temperatures
Allegra Mayer
1
*, Zeke Hausfather
2
, Andrew D. Jones
3
, Whendee L. Silver
1
Removal of atmospheric carbon dioxide (CO
2
) combined with emission reduction is necessary to keep climate warming
below the internationally agreed upon 2°C target. Soil organic carbon sequestration through agricultural management
has been proposed as a means to lower atmospheric CO
2
concentration, but the magnitude needed to meaningfully
lower temperature is unknown. We show that sequestration of 0.68 Pg C year
1
for 85 years could lower global tem-
perature by 0.1°C in 2100 when combined with a low emission trajectory [Representative Concentration Pathway (RCP)
2.6]. This value is potentially achievable using existing agricultural management approaches, without decreasing land
area for food production. Existing agricultural mitigation approaches could lower global temperature by up to 0.26°C
under RCP 2.6 or as much as 25% of remaining warming to 2°C. This declines to 0.14°C under RCP 8.5. Results were sen-
sitive to assumptions regarding the duration of carbon sequestration rates, which is poorly constrained by data. Results
provide a framework for the potential role of agricultural soil organic carbon sequestration in climate change mitigation.
INTRODUCTION
The uptake of atmospheric carbon (C) by plants and subsequent storage
in soils may be an effective means to lower atmospheric carbon dioxide
(CO
2
) concentrations and to help mitigate climate change. Integrated
assessment models (IAMs), which are used to explore future energy,
land-use, and greenhouse gas (GHG) emission scenarios, currently rely
on bioenergy with carbon capture and storage (BECCS) as a principal
negative emission technology to reach climate change mitigation targets,
butgenerallydonotconsiderthepossibility of C drawdown and soil
organic C (SOC) sequestration from improved land management (1,2).
Improved land management, without changing land use, may be an ad-
ditional C sequestration option that does not require more land con-
version. Land-use change and poor management practices have resulted
in the loss of more than 130 Pg C from agricultural soil (3), leaving
>1 billion hectares of degraded soil worldwide (4). Site-based studies
and ecosystem-scale models have shown that degraded and managed
agricultural lands have great potential to contribute to increased SOC
sequestration through improved management (57). We define soil C
sequestration as a net increase in SOC storage. Several agricultural
(cropland and grazing land) management practices have been shown
to increase soil C sequestration including organic amendments (810),
cover crops, reduced tillage, improved crop rotations (5,11,12), and im-
proved grazing management (13,14). Citing these proven practices and
others, France and 33 other countries recently instituted a challenge to
increase soil C by 4 per mil per year (15). However, the actual potential
of these practices to contribute to lowering global temperature over time
is poorly understood, despite recent efforts to quantify the amenable
global land area and near-term sequestration rates associated with various
practices (1618). This is primarily due to uncertainty regarding the
maintenance of soil C sequestration rates over time, the C sequestration
capacity of different soils under different managements, and the sen-
sitivity of global temperature changes to CO
2
emission and sequestration.
Here, we use a climate model emulator to translate SOC sequestra-
tion from agricultural management into a range of potential global
mean surface temperature changes over time, consistent with global-
scale outputs from the latest generation of Earth system models (ESMs;
see Materials and Methods and fig. S1). Much of the research to date on
the potential of land usebased SOC sequestration has focused on quan-
tifying current sequestration rates with the implicit assumption that
rates remain constant over time, often assuming a constrained time pe-
riod of 20 to 50 years (12,16). The potential for SOC sequestration to
contribute to a portfolio of mitigation strategies aimed at reducing cli-
mate change depends not only on the rates soon after C sequestering
practices are implemented but also on the time-integrated dynamics of
those rates, that is, how quickly land-use changes can be adopted, how
long they remain in effect, and how SOC stocks change over time (19).
This temporal dynamic is poorly understood but is critical to accurately
estimate the potential for land-based management to slow climate change.
In practice, rates of SOC sequestration are likely to decline over time
at any one site as soils reach new equilibria (20), but the time scale and
shape of these declines are not well constrained by data and are likely to
vary significantly among locations and management practices. To help
bound this uncertainty, we model the effects of SOC sequestration on
global surface temperature with and without consideration of effective
sequestration years, defined as the number of years it would take to
reach the maximum SOC stock (SOC max) at the current potential
sequestration rate (see fig. S3). The SOC max is a concept proposed
by Six et al.(21) and is poorly constrained by data at both site and global
scales. An SOC max provides a theoretical limit on the amount of SOC
storage in soils. As opposed to applying an arbitrary SOC max at a fixed
time period (for example, 20 or 50 years), we model effective sequestra-
tion years as a continuum of time periods required to reach an SOC max
(from 0 to 85 years) for a range of SOC sequestration rates. The current
potential sequestration rate was taken from values reported in the liter-
ature (table S1). Our analysis focuses specifically on the temperature re-
sponse to SOC sequestration. SOC storage is sensitive to a suite of global
change factors such as elevated atmospheric CO
2
concentration and
changes in climate, among others (22,23). These factors will likely have
additional, albeit poorly constrained, impacts on management-induced
SOC sequestration (24). Our goal here is not to quantify the ecological
controls on SOC storage and loss in agricultural ecosystems but to de-
termine the magnitude of SOC sequestration needed at a global scale to
meaningfully affect temperatures and to explore the sensitivity of atmo-
spheric temperature change to a range of possible temporal limits to soil
C sequestration (effective sequestration years).
1
Department of Environmental Science, Policy and Management, University of
California, Berkeley, Berkeley, CA 94720, USA.
2
Energy and Resources Group, Uni-
versity of California, Berkeley, Berkeley, CA 94720, USA.
3
Climate and Ecosystem
Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94705, USA.
*Corresponding author. Email: allegramayer@berkeley.edu
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RESULTS
The model shows that a global SOC sequestration rate of 0.68 Pg C year
1
from 2015 to 2100 would be required to yield a 0.1°C reduction in mean
surface temperature in target year 2100 when coupled with an aggressive
emission reduction scenario [Representative Concentration Pathway
(RCP)2.6;Fig.1].Theseresultsassumed a constant sequestration rate
tothetargetyear.The0.68PgCyear
1
global sequestration rate is at
the low end of the ranges of published estimates, which vary from a
low of 0.36 Pg C year
1
to a high of 1.56 Pg C year
1
(12,17,25,26). There
is considerable uncertainty in the actual time horizon of soil C sequestra-
tion rates within sites, which is likely to vary in response to social, econom-
ic, and biophysical factors (17,27). Few studies have measured long-term
(>20 years) patterns in soil C sequestration with agricultural management,
and those have shown a wide range of continued sequestration rates from
20 to over 150 years (11,2830).Forthisreason,weappliednoapriori
assumption on the time horizon required of soil C sequestration and, in-
stead, modeled a continuum of effective sequestration years at SOC
sequestration rates from 0 to 2.0 Pg C year
1
. It is important to note that,
while the model assumes constant annual rates of SOC sequestration at a
global scale, it does not require constant rates at individual sites.
Results were dependent on the underlying RCP scenario, assuming
3°C warming per doubling of CO
2
. In scenarios with greater emission
trajectories and thus higher atmospheric CO
2
concentrations (RCP 8.5
and RCP 6), greater SOC sequestration rates were required to reach the
same reduction in global surface temperatures due to the logarithmic
nature of CO
2
forcing (31). To achieve a 0.1°C reduction by the year
2100, the RCP 6.0 emission scenario would require a sequestration of
0.98 Pg C year
1
, while 1.25 Pg C year
1
would be required in the RCP
8.5 scenario. Management-based SOC sequestration had the highest
efficacy in the RCP 2.6 scenario, indicating the importance of simulta-
neous emission reductions and SOC sequestration activities resulting
from management. The sensitivity of climate to changes in atmospheric
CO
2
concentration is a key uncertainty in the model and had a large
influence on the temperature effect of C sequestration activities, as sce-
narios with lower climate sensitivity would require increased sequestra-
tion to result in the same temperature reduction (Fig. 1, black bars).
Estimates of climate sensitivity range from 1.5° to 4.5°C warming per
doubling CO
2
, with a median estimate of around 3°C (32).
A synthesis of the literature yielded a mean annual SOC sequestra-
tion potential from agriculture of 0.83 Pg C year
1
, with an upper value
of 1.78 Pg C year
1
(table S1). This value is greater than our estimate of
0.68 Pg C year
1
needed to reduce global temperatures by 0.1°C in 2100
under RCP 2.6 (Fig. 1), and results in a temperature reduction of 0.12°C
in 2100 if sustained for 85 years. Greater SOC sequestration and associated
temperature reduction may potentially be achieved with biochar amend-
ments (see the Supplementary Materials); this approach is less well constrained
than the other approaches and could require at least some utilization of
abandoned lands (10,33),andisthusnotconsideredfurtherhere.
Fig. 1. Impact of constant global rates of C sequestration (Pg C year
1
) on mean surface temperatures by target year (20162100) for a climate sensitivity of
3°C per doubling of atmospheric CO
2
.A 0.1°C reduction is highlighted by white lines. Different graphs indicate different RCP scenarios. Bars show the range of
continued C sequestration rates needed to achieve a 0.1°C reduction in 2050, 2075, and 2100, respectively, under a range of alternative climate sensitivities from 1.5°C
per doubling (upper bound) to 4.5°C per doubling (lower bound) (32). Upward arrows represent low CO
2
sensitivity upper bounds that are higher than the range of C
sequestration rates (0 to 2 Pg C year
1
) considered in this study; error bars are not symmetric around the 0.1°C reduction line due to nonlinearities in CO
2
forcing.
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Uncertainties in potential global rates of SOC sequestration with
improved land management can be partitioned into two primary
factors: the range of field-scale SOC sequestration rates reported for each
practice and the global land area over which the technique was considered
effective. Both area and rate assumptions affect the estimate of total SOC
sequestration potential. Area-dependent SOC sequestration rates varied from
0.02 to 1.15 Mg C ha
1
year
1
through improved cropland management
(12,34) and from 0.03 Mg C ha
1
year
1
(35)to0.62MgCha
1
year
1
through improved grazing land management (Table 1) (10,26). The
range of amenable land area varied from approximately 2900 Mha
for grazing land (36) to 400 Mha for cropland (16). We used the bio-
physical potential as the upper limit of SOC sequestration potential and
the minimum reported SOC sequestration estimate as the lower limit
(16,17,37). Nutrient availability at the field scale could theoretically limit
SOC sequestration rates (38,39), although the increase in soil organic
matter content can alleviate at least some of this limitation (18). We note
that agricultural management to increase SOC storage can interact
with soil inorganic C, by increasing storage or facilitating losses to the
atmosphere (40). However, the long-term impacts of SOC sequestration
on soil inorganic C dynamics are poorly understood. Economic con-
straints influenced the uncertainty regarding the amount of land
amenable to improved management (17,37), as well as whether man-
agement strategies could be implemented quickly and maintained over
multiple decades on the available and amenable land area. The manage-
ment practices explored here are likely to simultaneously provide the
co-benefit of improved soil fertility and water holding capacity, thus
increasing the financial desirability for implementation.
The results were sensitive to effective sequestration years (Fig. 2),
with the reduction in warming increasing roughly linearly with the
number of years that soils could continue to sequester C. If we assume
a limited effective sequestration period of 20 years (11,28), irrespective
of the mechanism limiting C storage, then the climate impact in the year
2100 associated with a sequestration rate of 0.83 Pg C year
1
decreased
from 0.12° to 0.03°C under RCP 2.6. If the effective sequestration period
is 50 years (12), then the climate impact in the year 2100 was 0.07°C
under RCP 2.6. These values highlight the potential negative impact
of short effective sequestration years. However, much of the worlds
soils are degraded with regard to SOC (4). Sanderman et al.(3)esti-
matedthat75and133PgChavebeenlostgloballyfromthetop1to
2 m of soil, respectively, due to human land use. If we assume that the
maximum soil C sequestration potential is equivalent to the amount of
C that has been lost from soils due to land use, then soils globally would
have the capacity to store an additional 0.9 Pg C year
1
until 2100 in the
top meter alone and 1.62 Pg C year
1
in the top 2 m. To determine the
impact of effective sequestration years on a given soil C sequestration
rate from any combination of management strategies, we assessed the
effect of the number of effective sequestration years (from 1 to 85) on
the year 2100 global mean surface temperatures for the range of SOC
sequestration rates (0 to 2.0 Pg C year
1
) previously considered (Fig. 2).
In practice, SOC sequestration rates would likely exhibit a gradual de-
clineovertime,andtheshapeofthisdeclinewouldlikelyvarybyland
use, climate, and soil type and is not well understood (41,42). Some
studies have found that SOC stocks reach an asymptote over time (28).
This can be indicative of the development of equilibrium conditions
under a given rate of inputs (11). It has also been hypothesized that
soils may become saturated with regard to SOC, with stocks ceasing
to increase even at increasing input rates (21,41,43,44). Understanding
of the long-term potential for soilsto sequester C is limited, and mech-
anisms such as C stabilization and protection are not consistently
represented in coupled climateC cycle models and major ESMs (45).
Our approach using effective sequestration years allows us to bound the
uncertainty arising from these poorly understood mechanisms.
DISCUSSION
Our results show that existing management strategies on current ag-
ricultural lands have the potential to reduce global temperatures by
the end of the century, sequestering as much as 1.78 Pg C year
1
.This
rate of sequestration could result in warming reductions of as much as
0.26°C in 2100 (assuming an effective sequestration period of at least
85 years). These model results are dependent on the effective seques-
tration years at a global scale and concurrent trends in emission reduc-
tion. The time horizon of SOC sequestration is poorly understood but
is critical for determining the long-term viability of these approaches.
In particular, we note that climate change is a millennial-scale phenom-
enon that stretches beyond the 2100 target. Therefore, the residence time
of organic C in soils, which can affect the long-term efficacy of SOC
sequestration (46), is an additional concern. SOC has the potential to
be stored for millennia [as evidenced by numerous radiocarbon studies
(47,48)], particularly when considering the entire soil depth profile (49),
but this may require a long-term commitment to maintaining soil C in
the future.
Management-based soil C sequestration strategies were significantly
more effective at reducing global warming under RCP 2.6 due to the
atmospheric saturation of CO
2
in high emission scenarios (for example,
in RCP 8.5). This result points to the value of combining aggressive
emission reduction with C removal strategies for climate change mitiga-
tion. The management strategies we evaluated here are different from
the measures assumed in the modeled RCP scenarios (50,51)andthere-
fore provide additional negative emissions if applied simultaneously
with emission reductions. The RCP scenarios can be realized through
many alternative energy, land-use, and land-cover pathways, but current
IAMs largely rely on land-cover change (for example, afforestation) and
C capture and storage technology combined with bioenergy (BECCS) to
reach goals of reduced radiative forcing (50). In contrast, this study
examined the effects of improving management practices on agricultural
Table 1. Published global estimates of management amenable agricultural land and the C sequestration potential of land management techniques.
Management Land type Range of published amenable
land area estimates (Mha)
Range of published potential C
sequestration rates (Mg C ha
1
year
1
)Sources
Improved cropland management Cropland 3801910 0.081.85 (16,17,26,34,36)
Improved grazing land management Grazing land 5002900 0.091.70 (16,17,26,35,36)
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land currently in production. We note that future changes in the overall
size of the agricultural land area will affect the area amenable to these
practices and that heavy reliance on bioenergy could compete with some
management activities on cropland or grazing land. This is one reason
that we emphasize consideration of a large range of possible sequestration
rates and time frames. Extensive adoption of land management strategies
could moderately reduce the need for BECCS, which is considered ex-
tensively in most 1.5° and 2°C target scenarios (52). Sequestering an
additional 1.78 Pg C year
1
through BECCS would require devoting
89 Mha of agricultural land to bioenergy production [equivalent to
roughly half of current global maize area harvested (53)]. Growing bio-
energy crops for BECCS on abandoned agricultural land could reduce
the impact on food prices and ecosystem carbon storage (33), although
lower crop yields and economic limitations on the use of abandoned
lands must be accounted for in this context (54).
Our analysis also points to the importance of the long-term potential
for SOC sequestration. The largely underappreciated scientific un-
certainty of effective sequestration years greatly affected the climate
change mitigation potential of land management strategies. A better
understanding of the long-term regional potential of specific man-
agement applications for C sequestration, as well as the controls and
limits on C sequestration, will facilitate better predictions of future land-
atmosphere C cycle feedbacks and also inform the potential for long-
term stabilization of C beyond the 2100 temperature target. As new
strategies are identified for sequestering C through land management
such as repurposing urban and rural nutrient and C waste streams
(7,55), our model provides a framework for translating these into
warming reductions.
MATERIALS AND METHODS
Climate model
We used a climate model that has been used previously in the literature
(5659) to evaluate the impact of emissions or emission reductions/C
sequestration on future transient climate responses (fig. S1). The model
takes a particular emission scenario for three major GHGs (CO
2
,CH
4
,
and N
2
O) and converts these emissions into atmospheric concentra-
tions, radiative forcing, and transient temperature response. This
emulator model has the benefit of enabling us to consider many possible
permutations of sequestration rates and effective sequestration years
while matching the global mean surface temperature response found
in more complex ESMs such as those included in the Coupled Model
Intercomparison Project 5 (CMIP5) featured in the Intergovernmental
Panel on Climate Change 5th Assessment Report (IPCC AR5; fig. S1).
Fig. 2. Impact of SOC sequestration rate (Pg C year
1
) and effective sequestration years on 2100 global mean surface temperature for a climate sensitivity of
3°C per doubling CO
2
with a 0.1°C reduction (highlighted by a white line). A range of potential C sequestration rates are shown in the center of the chart, as well as
their combined potential (black solid). The vertical dashed line shows the mean estimated potential of 0.83 Pg C year
1
for reference.
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As a single run of a coupled ESM would take 5 days, it would be pro-
hibitively difficult to perform the 6800 separate combinations of se-
questration rates and effective sequestration years examined in this paper.
To translate the rate of SOC sequestration into a transient global mean
surface temperature response, we perturbed the emission scenarios in the
RCPs by all possible sequestration rates between 0 and 3.0 Pg C year
1
from 2016 to 2100. We used simplified atmospheric lifetime functions for
each GHG (60) to calculate both perturbed and unperturbed atmospheric
CO
2
concentrations, translated these CO
2
concentrations into radiative
forcing (61), and used a continuous diffusion slab ocean model to
estimate transient temperature response (62). Reduction in warming
associated with sequestration rates was calculated from the difference
between the temperatures at a given point in time between the un-
perturbed and perturbed RCP scenario. We did not consider the
potential effects of temperature change on SOC dynamics as this was
beyond the scope of this study. These effects are poorly constrained,
and different studies find both increases and decreases of the SOC stock
with warming (24).
The model approximates the life cycle of each GHG using atmo-
spheric lifetime functions adapted from Joos et al.(60). These model
the percent of a discrete pulse remaining in the atmosphere after tyears
GCO2ðtÞ¼0:217 þ0:259et=172:9þ0:338et=18:51 þ0:186et=1:186
GCH4ðtÞ¼et=10
GN2OðtÞ¼et=114
CH
4
and N
2
O were assumed to have e-foldingtimesof10and114years
(for example, the time scale for a quantity to decrease to 1/eof its
initial value), respectively, while CO
2
reflects more complex C cycle
dynamics. These were converted into atmospheric concentrations
A
gas
(t) by treating each annual emission (or emission reduction) as
a discrete pulse and summing all pulse responses over the time pe-
riod of interest t
AgasðtÞ¼
n
i¼1EiGðttiÞ
where E
i
is the emissions in year iand G(tt
i
) is the fraction of the
gas remaining in the atmosphere after time tt
i
. The mass of each
gas in the atmosphere was converted into concentrations in parts per
million (ppm) [or parts per billion (ppb)] based on their respective
molar mass.
The resulting atmospheric GHG concentrations closely mirror the
results of CMIP5 runs (fig. S2) for the most part, although there is some
divergence in high emissions (RCP 6 and RCP 8.5) scenarios where
changes in ocean chemistry associated with acidification reduce the
airborne fraction in a manner not captured by our emulator model.
For this analysis, however, because we are looking at small perturbations
in the net CO
2
emissions of underlying RCP scenarios, the limitations of
the simple atmospheric carbon cycle model used should be minimal. We
did not explicitly consider feedbacks or interactions between carbon
sequestration and other GHG emissions (methane and nitrous oxide, in
particular). These fluxes were poorly constrained for most of the land uses
considered here, and thus, this was beyond the scope of the current analysis.
To convert atmospheric GHG concentrations into direct radiative
forcing, we used the simplified radiative forcing functions from the
IPCC AR5 (61). These are functional fits to more complicated absorp-
tion models derived from line-by-line radiative transfer functions that
have relatively small uncertainties: about 1% for CO
2
radiative forcing
and 10% for CH
4
radiative forcing calculations (31).
Forcing from a change in atmospheric concentration of CO
2
is
given by
DFCO2¼5:35ln ðPCO2þaCO2Þ
PCO2
Here, PCO2represents the initial concentration of CO
2
in the atmo-
sphere before the industrial era, while aCO2represents the additional
parts per million CO
2
added for any given scenario. For the purposes
of this analysis, PCO2was set to 277 ppm, the approximate value for the
preindustrial era (for example, 1765).
The direct radiative forcing of a given increase of CH
4
and/or
N
2
O in the atmosphere can be approximated by (61)
DFCH4¼0:036ðffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
PCH4þbCH4
pffiffiffiffiffiffiffiffiffi
PCH4
pÞ
fðPCH4þbCH4;PN2OÞþfðPCH4;PN2OÞ
DFN2O¼0:12ðffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
PN2OþbN2O
pffiffiffiffiffiffiffiffiffi
PN2O
pÞ
fðPCH4;PN2OþbN2OÞþfðPCH4;PN2OÞ
where
fðM;NÞ¼0:47 lnð1þ2:01105ðMNÞ0:75 þ
5:311015MðMNÞ1:52Þ
In this equation, PCH4is the initial concentration of atmospheric
CH
4
, while bCH4is the addition being evaluated. PN2Ois the initial
concentration of N
2
O, and bN2Ois the addition being evaluated. The
radiative forcing of both CH
4
and N
2
O is a function of the combination
of both, reflecting their interacting atmospheric chemistry. For this anal-
ysis, PCH4was set to 722 ppb and PN2Owas set to 272 ppm, reflecting
preindustrial atmospheric concentrations. f(M,N) is a function that
accounts for the interrelationship between CH
4
and N
2
Oforcing(61).
Radiative forcing was translated into a transient temperature re-
sponse by using a continuous diffusion slab ocean model adapted from
Caldeira and Myhrvold (62) and based on the study of Hansen et al.
(63). It is governed by the equations
DT
t¼kv
2DT
z2
DT
z
z¼0¼ðlDTDFðtÞÞ
pf cp;wkv
z¼0
DTt¼0¼0
j
DT
z
z¼zmax ¼0
where fis the fraction of the earth covered by ocean (0.71), pis the
density of water, c
p
is the heat capacity of water, z
max
is the maximum
ocean depth (4000 m), lis the feedback parameter (DT¼DF
lat equi-
librium, with l=1.25 chosen to reflect a climate sensitivity of 3 C per
doubling CO
2
), and k
v
is the ocean vertical thermal diffusivity (assumed
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to be 5.5 × 10
5
m
2
s
1
). The land fraction of the earth was assumed to
follow its equilibrium temperature response, with global surface tem-
peratures being the area-weighted average of the two.
Literature analysis
We used published global estimates of C sequestration potential in
grazing and croplands (table S1). Improved management approaches
included conversion to reduced or conservation till (12,17,64), crop
residue management (64,65), crop rotation and cover crop manage-
ment (12,17,66),optimizedirrigationandnutrient amendment strate-
gies (6,12,17), biochar amendments (10,16,26), increased productivity
of both cropland and grasslands (6,12,17), and improved grazing
management (17,25,26,35,67). To better determine the impact of soil
C sequestration on temperature, we used only estimates of soil C sinks,
and not addition or avoidance of CO
2
emissions due to management.
However, some global estimates account for nitrous oxide emissions
stimulated or avoided due to management, and report C estimates in
units of CO
2
eor C equivalents. We therefore compared global estimates
using the unit CO
2
e-C, which was converted using the ratio of atomic
mass: 1 Pg C = 12/44 × 1 Pg CO
2
e. We reported estimates for biochar
separately because of continuing interest in biochar as a means to se-
quester atmospheric CO
2
despite poorly constrained estimates of its
persistence in soil and notwithstanding its potential land conversion re-
quirements (10,25,33,68). Other management strategies, including
compost and other organic amendments, could also be applied over
large and diverse areas, but large-scale estimates for the potential of C
sequestration from these strategies are lacking.
We differentiated between total soil C sequestration potential and
the combined potential. Total C sequestration potential is an aggrega-
tion of literature estimates of the total global agricultural C sink potential
(12,17,25,26,37). For the combined potential, we summed recent land-
use and management-specific estimates for potential sequestration in
cropland (16,17,26,34,69) and grazing lands (16,17,26,35,69)together
with the available land area given in the same sources for these practices.
We report this combined potential with and without biochar contribu-
tions, as biochar application can be used alone or coupled with other
land-use practices for the same land area. Values given in the text are
means ± 1 SE when multiple estimates were available.
SUPPLEMENTARY MATERIALS
Supplementary material for this article is available at http://advances.sciencemag.org/cgi/
content/full/4/8/eaaq0932/DC1
Fig. S1. SimMod emulator climate model transient (solid red) temperature response compared
to CMIP5 multimodel mean (black line) and 2.5 to 97.5% spread (gray area) for each RCP
scenario.
Fig. S2. RCP (solid lines) and SimMod emulator climate model (dashed lines) atmospheric
concentrations of CO
2
,N
2
O, and CH
4
for each scenario (53).
Fig. S3. A schematic illustration of the concept of effective sequestration years (ESY).
Fig. S4. Same as Fig. 2 in the text but with the inclusion of biochar and for a range of
sequestration rates from 0 to 3 Pg C year
1
.
Table S1. Summary of global soil C sequestration potential (Pg C year
1
) by agricultural land
management.
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Acknowledgments: We thank P. Smith for advice, support, and help with data
interpretation. We also thank B. Collins for supporting the conception of the project, I. Fung
for her challenge and friendly review, and J. Wick for encouragement. Funding: We thank the
Rathmann Family Foundation for funding this project. This work was supported in part by the
U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research
under contract DE-AC02-05CH11231. Author contributions: A.M. contributed to conceptual
development, conducted literature review, made figures, and led the writing effort. Z.H.
contributed to conceptual development, updated and ran the carbon-climate model, made
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figures, and contributed to writing. A.D.J. and W.L.S. guided conceptual development and
contributed to writing. W.L.S. conceived the project. Competing interests: The authors declare
that they have no competing interests. Data and materials availability: The simple CMIP
emulator model used in this analysis along with the underlying RCP scenario emissions
are available on GitHub (https://github.com/hausfath/SimMod). All data needed to evaluate the
conclusions in the paper are present in the paper and/or the Supplementary Materials.
Additional data related to this paper may be requested from the authors.
Submitted 29 September 2017
Accepted 23 July 2018
Published 29 August 2018
10.1126/sciadv.aaq0932
Citation: A. Mayer, Z. Hausfather, A. D. Jones, W. L. Silver, The potential of agricultural land
management to contribute to lower global surface temperatures. Sci. Adv. 4, eaaq0932 (2018).
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temperatures
The potential of agricultural land management to contribute to lower global surface
Allegra Mayer, Zeke Hausfather, Andrew D. Jones and Whendee L. Silver
DOI: 10.1126/sciadv.aaq0932
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... Soils retain the water that plants and soil organisms use to survive and grow, and slow the rate of water movement and thus limit the rate of erosion and soil loss [3]. Soils also contribute to the composition of the atmosphere, and by association impact climate, and are both a significant source and sink of greenhouse gases [4,5]. At a societal level, one of the most obvious contributions of soil to people is the role that soils play in the provision of food for human populations and feed for livestock. ...
... Several soil management approaches have been proposed to address the increased need for food. These include shifts to more nutrient-efficient diets [121], strategic intensification and technological improvements [29], restoration and maintenance of soil fertility and stability [122] and enhancing resilience in the face of climate change [5,123]. Feed crops currently account for almost 40% of global agricultural production, including the use of some of the most fertile soils in the world. ...
... Enhancing soil organic matter content has also been proposed as a means to rehabilitate nutrient retention in soils. Increased soil organic matter stocks not only promotes higher yields and soil quality but also provides a co-benefit for climate change mitigation through increased soil C storage and decreased greenhouse gas emissions relative to other fertilizers [5,[135][136][137]. ...
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Soils play a critical role in the production of food and feed for a growing global population. Here, we review global patterns in soil characteristics, agricultural production and the fate of embedded soil nutrients. Nitrogen- and organic-rich soils supported the highest crop yields, yet the efficiency of nutrient utilization was concentrated in regions with lower crop productivity and lower rates of chemical fertilizer inputs. Globally, soil resources were concentrated in animal feed, resulting in large inefficiencies in nutrient utilization and losses from the food system. Intercontinental transport of soil-derived nutrients displaced millions of tonnes of nitrogen and phosphorus annually, much of which was ultimately concentrated in urban waste streams. Approximately 40% of the global agricultural land area was in small farms providing over 50% of the world's food and feed needs but yield gaps and economic constraints limit the ability to intensify production on these lands. To better use and protect soil resources in the global food system, policies and actions should encourage shifts to more nutrient-efficient diets, strategic intensification and technological improvement, restoration and maintenance of soil fertility and stability, and enhanced resilience in the face of global change. This article is part of the theme issue ‘The role of soils in delivering Nature's Contributions to People’.
... Several studies reported agricultural management practices that are found to be beneficial to sequester carbon from various regions in the world (see the literature review and listed sequestration rates in [8]. Addition of organic amendments to the soil is one of the more reported management practices to increase SOC, along with other agricultural practices [14][15][16][17][18] such us reduced tillage [19][20], crop residue incorporation [20][21][22], cover crops [23][24], crop rotation [20], [25] or land use changes [26][27][28]. Moreover, organic farming [4], [29][30][31] and conservation agriculture [32] are reported to effectively promote carbon sequestration when compared to conventional agriculture. ...
... Moreover, organic farming [4], [29][30][31] and conservation agriculture [32] are reported to effectively promote carbon sequestration when compared to conventional agriculture. Most of these recommended practices are supposed to increase SOC by themselves but some studies have highlighted the potential of combining practices to improve sequestration [16][17][18]. Moreover, there are studies on upscaling the effects of SOC on climate change, land use changes or the application of certain agricultural practices [15], [26], [33]. ...
... Moreover, there are studies on upscaling the effects of SOC on climate change, land use changes or the application of certain agricultural practices [15], [26], [33]. However, compost or organic amendments large scale estimates for the carbon sequestration potential of compost and organic amendments in agricultural soils are still scarce [18]. ...
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Soil organic carbon (SOC) plays an important role on improving soil conditions and soil functions. Increasing land use changes have induced an important decline of SOC content at global scale. Increasing SOC in agricultural soils has been proposed as a strategy to mitigate climate change. Animal manure has the characteristic of enriching SOC, when applied to crop fields, while, in parallel, it could constitute a natural fertilizer for the crops. In this paper, a simulation is performed using the area of Catalonia, Spain as a case study for the characteristic low SOC in the Mediterranean, to examine whether animal manure can improve substantially the SOC of agricultural fields, when applied as organic fertilizers. Our results show that the policy goals of the 4 × 1000 strategy can be achieved only partially by using manure transported to the fields. This implies that the proposed approach needs to be combined with other strategies.
... 9 t CO 2 eq) 、工业生产过程(17.18×10 9 t CO 2 eq) 、农业活动(8.30×10 9 t CO 2 eq) 、废弃物处理(1.95×10 9 t CO 2 eq) ,土地利用、土地利用变化和林业(-11.15×10 9 t CO 2 eq) ,其中农业活动占比为 7.42% [2] 。从全生命周期的视角来看,将种植、加工等环节 纳入核算体系,2007-2016 年间全球农业、林业和土地利用部门的 GHG 排放占到全球总 净排放的 21%~37% [3] 。2015 年全球食物系统的 GHG 排放达到 180×10 9 t CO 2 eq(中国 24 (1)水稻种植。淹水的条件下,稻田土壤中的腐烂植物体等有机物被产甲烷细菌分 解而产生 CH 4 。关于水稻种植 CH 4 减排措施已有较多研究,一是持续推进水稻生长季节稻 田排水 [6] ;二是开发高产低碳排放的水稻品种 [7] ;三是调节土壤中硫酸盐含量,通过硫酸 盐还原菌与产甲烷细菌竞争底物来实现 CH 4 减排 [8] ;四是采用覆膜技术减少水稻种植用水 [9] ;五是提高土壤的有机质含量并采用高产新品种 [10] 。另外,将稻草从被淹的稻田中移除 有助于 CH 4 的减排,但是这也将导致钾、硅等元素的流失,不利于土壤健康,但也有研究 发现通过有效的作物和土壤管理并不会降低土壤肥力,目前关于稻草从田间移除的利弊尚 不明确 [11,12] 。 (2)动物肠道发酵。动物肠道发酵排放 CH 4 ,其中反刍动物贡献最大。研究发现, 即使我国最高效的生产系统与发达国家相比,牛奶和牛肉生产的 GHG 排放强度仍分别高 27%和 59% [13] 。目前,减少动物性食物的消费被多数学者提出是降低食物来源碳排放的主 要措施之一 [14] 。除了降低动物性食物消费,其他减排途径主要有:一是添加有助于减排的 饲料添加剂 [15] 和甲烷抑制剂 [16] ;二是提高饲料利用率 [17] ;三是提高动物的生产力和健康, 包括通过提高优良性状遗传潜力和繁殖力缩小养殖规模,并进一步提高增重率来缩短养殖 周期 [15] ;四是集约化养殖,提高资源利用率和管理效率。 (3)动物粪便管理。动物粪便管理同时产生 CH 4 与 N 2 O。动物粪便产生量、储存温 度、储存时长以及厌氧分解是影响 CH 4 产生的主要因素 [14] ,因此在动物粪便管理过程中应 注重饲养空间、干湿分离并及时转运粪便。动物粪便 N 2 O 排放的主要途径是硝化作用和反 硝化作用 [18] 。N 2 O 直接排放取决于粪便的碳氮含量、储存时长和处理方式,并随着环境酸 度、硝酸盐浓度的增加与水分的减少而增加 [14] 。N 2 O 间接排放来源于粪便收集和储运过程 中的 NH 3 和 NO X 挥发性氮损失、因浸出和径流造成的氮损失以及粪尿在土壤中的沉积。 因此,一是通过适量储存粪便来减少因挥发和淋溶导致的氮损失 [19] ;二是压实和覆盖动物 粪便来避免养分流失到环境中 [20] ;第三,使用包括硝化反应抑制剂在内的抑制 N 2 O 排放 技术 [21] 。再者,不同的田间粪肥施用时间和管理方式可能导致 GHG 排放相差几倍 [15] 。另 外,施用粪肥部分替代无机肥料可以减少工业部门的生产投入,实现 GHG 的全生命周期 减排 [22,23] 。 (4)农用地管理。通过提升农用地管理有助于增加土壤碳固存、减少碳排放 [24] 。具 体措施有:一是,提高作物单位面积产量、减少农业用地面积、恢复节约土地的植被生境 [25] ;二是,提高化肥利用率,优化灌溉管理 [26] ;三是,系列农业管理措施,比如生物炭等 有机改良剂 [27,28] 、作物轮作 [29] 、秸秆还田 [30] 、放牧管理 [31] 等;四是,需要重视耕地弃耕 抛荒问题。 对于弃耕耕地, 一般可以经历次生演替使得生态系统恢复到农业前的植被状态, 并且能将碳固定在植被和土壤中 [32] 。然而,在某些情况下,弃耕耕地的生态系统恢复力很 弱或者根本不会恢复,这需要针对弃耕耕地的生态管理措施的介入,最大程度发挥耕地的 碳捕获和碳固存能力 [33,34] 水肥一体化 减排 35.15% 10%成效 20%成效 [27] 推广生物炭等有机改良剂 减排 23.33% 10%成效 20%成效 [28] 农业土 壤固碳 秸秆还田 固碳 225 kgCO 2 eq/1000 kg 秸秆 还田比例 80% 还田比例 90% [34] 图 7 齐齐哈尔市农业 GHG 排放与固碳历史变化趋势与情景模拟 ...
Article
碳达峰、碳中和目标对我国农业绿色发展提出了更高要求,实现农业减排固碳目标与农业绿色发展政策协同发展至关重要。本文综合运用文献归纳、政策文本分析等方法,全面分析梳理了农业温室气体排放核算框架、农业减排固碳措施研究进展,刻画了1978年以来我国与农业减排固碳相关的农业绿色发展政策的演进历程,定性评价了农业绿色发展政策与农业减排固碳目标之间的协同关系,并且以黑土区齐齐哈尔市为研究区模拟了不同农业减排固碳与农业绿色发展政策协同情景下的农业减排固碳演变趋势。结果显示,农业减排固碳目标与大部分现行农业绿色发展政策目标是协同推进的,但在水稻种植、畜禽养殖、秸秆利用、种植结构调整等方面也存在无作用、甚至负协同的目标;通过政策目标调整,在不同的农业减排固碳技术组合情景下,黑土区能够促进农业温室气体减排与固碳的脱耦,最终实现减排与固碳的双赢。基于此,提出了重视农业减排固碳在促进“双碳”目标中的基础性作用,统筹将农业减排固碳、促进“双碳”目标纳入政策目标,并理顺二者政策目标关系的对策建议,以期为“双碳”目标下的农业绿色发展政策制定提供参考借鉴。 Carbon peak and carbon neutral targets have put forward new objectives for the green development of agriculture in China; therefore, it is very important to achieve synergetic development between agricultural greenhouse gas (GHG) emission reduction, carbon sequestration, and policies for agricultural green development. This study omprehensively analyzed and compared the accounting framework of agricultural GHG emissions and the research progress of the measures of agricultural GHG emission reduction and carbon sequestration by means of literature summaries and policy analysis and described the evolution process of agricultural green development policies related to agricultural GHG emission reduction and carbon sequestration since 1978. The synergistic relationship between agricultural green development policies and agricultural GHG emission reduction and carbon sequestration targets was qualitatively evaluated, and the changing trend of agricultural GHG emission reduction and carbon sequestration under the coordination of different agricultural green development policies was simulated in a black soil area. The results showed that the targets of GHG emission reduction and carbon sequestration in agriculture were coordinated with most of the current targets of agricultural green development policies, but there were some targets that were not included or even negatively coordinated in rice planting, livestock and poultry breeding, straw utilization, and adjustment of planting structure. Through the adjustment of policy objectives, under different combinations of agricultural GHG emission reduction and carbon sequestration technologies in comparison with historical trends, it can promote the decoupling of gricultural GHG emission reduction and carbon sequestration in the black soil region, and finally achieve a win-win situation of agricultural GHG emission reduction and carbon sequestration. Based on these results, several suggestions are proposed, including paying attention to the fundamental role of agricultural GHG emission reduction and carbon sequestration in the carbon peak and carbon neutral targets, expanding the dimensions of agricultural policies, incorporating agricultural GHG emission reduction and carbon sequestration into the targets of agricultural policies, and coordinating the relationship between the two objectives. It is expected to provide a reference for the policy formulation of agricultural green development against the background of carbon peak and carbon neutrality.
... Meta-analysis by Poeplau and Don (2015) from 30 studies with 139 plots at 37 sites estimated that cover crops can globally sequester 0.12 ± 0.03 Pg C yr − 1 , which would offset 8% of the annual direct agricultural GHG emissions with ability to lower Earth's temperature by 0.1-0.26 • C (Mayer et al., 2018). ...
Article
Due to increased contribution from agriculture sector to total greenhouse gas emissions, there is need to study the ability of no-tilled diverse cropping systems including crop sequences and bio-covers to mitigate C equivalent emissions. Thus, C-footprint was calculated for a long-term experiment at the University of Tennessee's Research and Education Center in Milan with six-crop sequences: continuous cotton (Gossypium hirsutum L.), cotton-corn (Zea mays L.), continuous corn, corn-soybean (Glycine max L.), continuous soybean, and soybean-cotton interacted with four bio-covers: poultry litter, hairy vetch (Vicia villosa), winter wheat (Triticum aestivum), and fallow control with three replicates in a strip-plot design. During the experiment duration (2002-2017), field inputs (fertilizers, pesticides, and machinery used for planting, chemical applications, and harvesting) and outputs (crop yield, aboveground, and belowground residue) were assessed for each crop sequence/bio-cover combination to calculate total C equivalence of inputs and outputs, net C gain, C footprint per kg yield, sustainability index, and nitrous oxide emissions. For continuous corn, C-based input emissions were significantly higher by 0.28-0.62 Mg CO 2 eq. ha − 1 yr − 1 than all other sequences, however, a greater net C gain (5.4 Mg C eq. ha − 1 yr − 1) was also observed due to increased crop yield, aboveground and belowground residues. Poultry litter application resulted in lower C-footprint (1.59-2.09 kg CO 2 eq. kg − 1 yield) than hairy vetch, wheat, and fallow under all crop sequences. Hairy vetch also lowered C-footprint per kg yield (~2-14%) when compared with wheat under continuous systems of corn, soybean, and cotton, and cotton-corn rotation. Poultry litter application increased sustainability index (23-45) of all cropping sequences compared with other bio-covers. Hairy vetch improved sustainability index of corn including cropping sequences as compared with wheat and fallow. Inclusion of soybean and cotton with corn significantly decreased nitrous oxide emissions by 20-25%. The major factor contributing towards C-based input emissions was N fertilizer with 68% contribution to total emissions on average. It is concluded that application of poultry litter can reduce per yield C-footprint and enhance production system sustainability compared with hairy vetch, wheat, and fallow for monocultures or rotations of corn, soybean, cotton. Additionally, hairy vetch can outperform wheat in reducing the per yield C-footprint for continuous corn/soybean/cotton, and cotton-corn rotation. Especially for corn production systems, hairy vetch can enhance sustainability index compared with wheat and fallow. In order to increase per hectare net C gain, reduce per yield C-footprint and enhance sustainability index simultaneously, integration of continuous corn or corn-soybean/cotton rotation with bio-cover poultry litter or hairy vetch may perform better than the mono-cultures of soybean or cotton integrated with bio-cover wheat or fallow control in the Mid-south USA.
... Moreover, training and better agricultural facilities and technologies are also effective measures to enable adaptation to the adverse effects of climate change 28 . Improving cropland NUE and managing agricultural land sustainably would in turn slow down the rise in temperature rising reduction of greenhouse gas emission from agriculture 29,30 . Thus, early actions should be taken to ease the projected future impact of climate change on agriculture to achieve the global sustainable goals 31,32 . ...
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Maintaining food production while reducing agricultural pollution is a grand challenge under the threats of global climate change, which has exerted negative impacts on agricultural sustainability. How agricultural nitrogen use and loss respond to climate change is rarely understood. Here we show that climate change leads to inequality of cropland nitrogen use and loss across global regions based on historical data for the period 1961-2018 from 143 countries. Increases of yield, nitrogen surplus and nitrogen use efficiency (NUE) are identified in 30% of countries, while reductions are observed for the remaining 70% of countries, as a result of climate change. Farm size changes further intensify the inequality of nitrogen use and pollution in global croplands. Yet, enlarging farm size can facilitate climate change adaptation, by which global cropland NUE could be increased by one-third in 2100 compared to 2018 under future shared socioeconomic pathways. Our results would be of great significance to sustain global agriculture as well as eliminate national inequalities on food production and agricultural pollution control.
... Soils harbor more carbon worldwide than is stored in both the phytomass and the atmosphere (Scharlemann et al. 2014;Sulman et al. 2018). In particular, the potential of agricultural soils to sequester carbon has been recently discussed under the notion of climate change mitigation (Mayer et al. 2018;Loisel et al. 2019;Bossio et al. 2020). Interactions between soil organic carbon (OC) and mineral soil particles reduce the accessibility of OC for degraders, governing its susceptibility to mineralization and release into the atmosphere (Torn et al. 1997;Schmidt et al. 2011;Kleber et al. 2015Kleber et al. , 2021. ...
Article
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Correlations between organic carbon (OC) and fine mineral particles corroborate the important role of the abundance of soil minerals with reactive surfaces to bind and increase the persistence of organic matter (OM). The storage of OM broadly consists of particulate and mineral-associated forms. Correlative studies on the impact of fine mineral soil particles on OM storage mostly combined data from differing sites potentially confounded by other environmental factors. Here, we analyzed OM storage in a soil clay content gradient of 5–37% with similar farm management and mineral composition. Throughout the clay gradient, soils contained 14 mg OC g ⁻¹ on average in the bulk soil without showing any systematic increase. Density fractionation revealed that a greater proportion of OC was stored as occluded particulate OM in the high clay soils (18–37% clay). In low clay soils (5–18% clay), the fine mineral-associated fractions had up to two times higher OC contents than high clay soils. Specific surface area measurements revealed that more mineral-associated OM was related to higher OC loading. This suggests that there is a potentially thicker accrual of more OM at the same mineral surface area within fine fractions of the low clay soils. With increasing clay content, OM storage forms contained more particulate OC and mineral-associated OC with a lower surface loading. This implies that fine mineral-associated OC storage in the studied agricultural soils was driven by thicker accrual of OM and decoupled from clay content limitations.
... reservoir of SOC has undergone depletion due to land cover changes and unsustainable land management in the Anthropocene (Paustian et al. 1997, Amundson et al. 2015, Harden et al. 2017, Sanderman et al. 2017. The potential to reverse these trends via management practices is currently debated (Minasny et al. 2017, Amundson andBiardeau 2018), but evidence suggests that increased SOC storage in agricultural lands alone has the potential to detectably reduce the atmospheric CO 2 burden (Griscom et al. 2017, Mayer et al. 2018. Collectively, these observations and concerns underscore the importance of advancing our ability to identify the environmental conditions linked to SOC input, losses, and retention (Smith et al. 2019) and, ultimately, to understand the mechanisms driving patterns of SOC distributions within and among ecosystems. ...
Article
Soil organic carbon (SOC) regulates terrestrial ecosystem functioning, provides diverse energy sources for soil microorganisms, governs soil structure, and regulates the availability of organically‐bound nutrients. Investigators in increasingly diverse disciplines recognize how quantifying SOC attributes can provide insight about ecological states and processes. Today, multiple research networks collect and provide SOC data, and robust, new technologies are available for managing, sharing, and analyzing large data sets. We advocate that the scientific community capitalizes on these developments to augment SOC datasets via standardized protocols. We describe why such efforts are important and the breadth of disciplines for which it will be helpful, and outline a tiered approach for standardized sampling of SOC and ancillary variables that ranges from simple to more complex. We target scientists ranging from those with little to no background in soil science to those with more soil‐related expertise, and offer examples of the ways in which the resulting data can be organized, shared, and discoverable.
... Land-use and -cover change (LUCC) is a key variable in most of the decarbonization modeling scenarios for achieving this goal (e.g. biomass energy with carbon capture and storage, afforestation, reforestation) [2][3][4], as it can be both a large source [5][6][7] and sink [8][9][10] of carbon emissions. However, decarbonization is just one of several, sometimes competing, values derived from land use, which complicates both the estimation of achievable carbon benefits and the development of regional policies for realizing those potentials. ...
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Land-use and -cover change (LUCC) is globally important to climate change mitigation. However, using land-based strategies to support aggressive subnational greenhouse gas emissions reduction targets is challenging due to competing land use priorities and uncertainty in ecosystem carbon dynamics and climate change effects. We used the California natural and working lands carbon and greenhouse gas model to quantify the direct ecosystem carbon emissions (CO2 and CH4) impacts, trade-offs, and climate change interactions of two policy scenarios identified by the State of California for fulfilling multiple land use goals, including the competing goals of mitigating wildfire severity and landscape carbon emissions, among others. Here we show that emissions from desired forest management to reduce the amount of combustible biomass (fuel reduction) initially outweighed emissions reductions from other strategies (e.g. less intensive forest management, restoration, land conservation); however, avoided emissions and enhanced carbon sequestration from the other strategies gradually outweighed fuel reduction emissions. Thus, in jurisdictions with large-scale wildfire mitigation goals, practices that reduce emissions and/or increase carbon sequestration can simultaneously offset fuel reduction emissions. Our analysis highlights the complexities inherent in LUCC planning, underscoring the need for governments to begin the task now.
... Managing and conservating the soil C is more effective way towards climate change adaptation and mitigation strategies which reduces the concentration of atmospheric CO 2 (Mayer et al. 2018). Therefore, the information regarding the SOC and associated C sequestration potential in the soil ecosystem is essential step to determine the source and sink of C altered by various biotic influences. ...
Chapter
The land resource and other natural resources are degrading day by day due to human greed of development and unsustainable management. These will not only affect the ecosystem structure and related services but also disturb environmental sustainability and overall ecological stability at global scale. Today, climate change becomes most highlighted and burning issue among policy makers, stakeholders, scientists, and academicians across various national and international platforms. However, the climate change and other perturbation have altered the natural balance of different ecosystems resulting into poor ecosystem services. This will not only affect yield and productivity but also affect ecosystem health in many dimensions. In this context, capturing of carbon (C) through the process of C sequestration will increase C values in vegetation and soil as soil organic carbon (SOC) pools that directly or indirectly link with food-soil-climate security. Soil organic matter (SOM) and C are the key management strategies for managing land resources wisely. Updated and advance technologies of soil C-friendly management are the major mitigatory strategy for different ecosystems. Soil C management requires the practices which add C inputs in soil instead removing the soil C and nutrients reserve. The land-use systems must be eco-friendly and sustainable one to stop the land degradation and deterioration. Sustained research and developmental activities are needed to generate C dynamics knowledge base which subsequently helps to visualize the changes in soil C quantity and impact on the atmospheric C. Moreover, this information supports for terrestrial C management and climate change adaptation and mitigation. In the view of the above, a rigorous and comprehensive discussion has been made on soil C sequestrations in varying land use practices (forest, agroforestry, and fruits based land use system, etc.) and its role in climate change mitigation to achieve the goal of sustainable environment and maintaining overall ecological stability.
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Harnessing nature-based climate solutions (NbCS) to help simultaneously achieve climate and conservation goals is an attractive win-win. The contribution of NbCS to climate action relies on both biogeochemical potential and the ability to overcome environmental, economic and governance constraints for implementation. As such, estimates of additional NbCS-related terrestrial biosphere storage potential range from less than 100 GtCO2 to more than 800 GtCO2. In this Review, we assess the negative emissions contributions of NbCS — including reforestation, improved forest management and soil carbon sequestration — alongside their environmental, social and governance constraints. Given near-term implementation challenges and long-term biogeochemical constraints, a reasonable value for the expected impact of NbCS is up to 100–200 GtCO2 in negative emissions for the remainder of the twenty-first century. To sustainably reach this level, focus should be on projects with clear co-benefits, and must not come at the expense of a reduction in emissions from deforestation and forest degradation, rapid decarbonization and innovation from alternative negative emissions technologies.
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The role of soil organic carbon in global carbon cycles is receiving increasing attention both as a potentially large and uncertain source of CO2 emissions in response to predicted global temperature rises, and as a natural sink for carbon able to reduce atmospheric CO2. There is general agreement that the technical potential for sequestration of carbon in soil is significant, and some consensus on the magnitude of that potential. Croplands worldwide could sequester between 0.90 and 1.85 Pg C/yr, i.e. 26–53% of the target of the “4p1000 Initiative: Soils for Food Security and Climate”. The importance of intensively cultivated regions such as North America, Europe, India and intensively cultivated areas in Africa, such as Ethiopia, is highlighted. Soil carbon sequestration and the conservation of existing soil carbon stocks, given its multiple benefits including improved food production, is an important mitigation pathway to achieve the less than 2 °C global target of the Paris Climate Agreement.
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Better stewardship of land is needed to achieve the Paris Climate Agreement goal of holding warming to below 2 °C; however, confusion persists about the specific set of land stewardship options available and their mitigation potential. To address this, we identify and quantify "natural climate solutions" (NCS): 20 conservation, restoration , and improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands. We find that the maximum potential of NCS-when constrained by food security, fiber security, and biodiversity conservation-is 23.8 petagrams of CO 2 equivalent (PgCO 2 e) y −1 (95% CI 20.3-37.4). This is ≥30% higher than prior estimates, which did not include the full range of options and safeguards considered here. About half of this maximum (11.3 PgCO 2 e y −1) represents cost-effective climate mitigation, assuming the social cost of CO 2 pollution is ≥100 USD MgCO 2 e −1 by 2030. Natural climate solutions can provide 37% of cost-effective CO 2 mit-igation needed through 2030 for a >66% chance of holding warming to below 2 °C. One-third of this cost-effective NCS mitigation can be delivered at or below 10 USD MgCO 2 −1. Most NCS actions-if effectively implemented-also offer water filtration, flood buffer-ing, soil health, biodiversity habitat, and enhanced climate resilience. Work remains to better constrain uncertainty of NCS mitigation estimates. Nevertheless, existing knowledge reported here provides a robust basis for immediate global action to improve ecosystem stewardship as a major solution to climate change. climate mitigation | forests | agriculture | wetlands | ecosystems
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Human appropriation of land for agriculture has greatly altered the terrestrial carbon balance, creating a large but uncertain carbon debt in soils. Estimating the size and spatial distribution of soil organic carbon (SOC) loss due to land use and land cover change has been difficult but is a critical step in understanding whether SOC sequestration can be an effective climate mitigation strategy. In this study, a machine learning-based model was fitted using a global compilation of SOC data and the History Database of the Global Environment (HYDE) land use data in combination with climatic, landform and lithology covariates. Model results compared favorably with a global compilation of paired plot studies. Projection of this model onto a world without agriculture indicated a global carbon debt due to agriculture of 133 Pg C for the top 2 m of soil, with the rate of loss increasing dramatically in the past 200 years. The HYDE classes "grazing" and "cropland" contributed nearly equally to the loss of SOC. There were higher percent SOC losses on cropland but since more than twice as much land is grazed, slightly higher total losses were found from grazing land. Important spatial patterns of SOC loss were found: Hotspots of SOC loss coincided with some major cropping regions as well as semiarid grazing regions, while other major agricultural zones showed small losses and even net gains in SOC. This analysis has demonstrated that there are identifiable regions which can be targeted for SOC restoration efforts.
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The '4 per mille Soils for Food Security and Climate' was launched at the COP21 with an aspiration to increase global soil organic matter stocks by 4 per 1000 (or 0.4 %) per year as a compensation for the global emissions of greenhouse gases by anthropogenic sources. This paper surveyed the soil organic carbon (SOC) stock estimates and sequestration potentials from 20 regions in the world (New and Russia). We asked whether the 4 per mille initiative is feasible for the region. The outcomes highlight region specific efforts and scopes for soil carbon sequestration. Reported soil C sequestration rates globally show that under best management practices, 4 per mille or even higher sequestration rates can be accomplished. High C sequestration rates (up to 10 per mille) can be achieved for soils with low initial SOC stock (topsoil less than 30 t C ha −1), and at the first twenty years after implementation of best management practices. In addition, areas which have reached equilibrium will not be able to further increase their sequestration. We found that most studies on SOC sequestration only consider topsoil (up to 0.3 m depth), as it is considered to be most affected by management techniques. The 4 per mille number was based on a blanket calculation of the whole global soil profile C stock, however the potential to increase SOC is mostly on managed agricultural lands. If we consider 4 per mille in the top 1m of global agricultural soils, SOC sequestration is between 2-3 Gt C year −1 , which effectively offset 20–35% of global anthropogenic greenhouse gas emissions. As a strategy for climate change mitigation, soil carbon sequestration buys time over the next ten to twenty years while other effective sequestration and low carbon technologies become viable. The challenge for cropping Geoderma j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / g e o d e r m a farmers is to find disruptive technologies that will further improve soil condition and deliver increased soil carbon. Progress in 4 per mille requires collaboration and communication between scientists, farmers, policy makers, and marketeers.
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Rising levels of atmospheric CO2 frequently stimulate plant inputs to soil, but the consequences of these changes for soil carbon (C) dynamics are poorly understood. Plant-derived inputs can accumulate in the soil and become part of the soil C pool ("new soil C"), or accelerate losses of pre-existing ("old") soil C. The dynamics of the new and old pools will likely differ and alter the long-term fate of soil C, but these separate pools, which can be distinguished through isotopic labeling, have not been considered in past syntheses. Using meta-analysis, we found that while elevated CO2 (ranging from 550 to 800 parts per million by volume) stimulates the accumulation of new soil C in the short term (<1 year), these effects do not persist in the longer term (1-4 years). Elevated CO2 does not affect the decomposition or the size of the old soil C pool over either temporal scale. Our results are inconsistent with predictions of conventional soil C models and suggest that elevated CO2 might increase turnover rates of new soil C. Because increased turnover rates of new soil C limit the potential for additional soil C sequestration, the capacity of land ecosystems to slow the rise in atmospheric CO2 concentrations may be smaller than previously assumed.