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O R I G I N A L P A P E R
Adaptation and mitigation strategies in agriculture:
an analysis of potential synergies
Cynthia Rosenzweig Æ Francesco Nicola Tubiello
Received: 8 May 2006 / Accepted: 23 May 2006 / Published online: 19 April 2007
! Springer Science+Business Media B.V. 2007
Abstract As climate changes due to rising concentrations of greenhouse gases in the
atmosphere, agriculture will be one of the key human activities affected. Projections show
that while overall global food production in the coming decades may keep pace with the
food requirements of a growing world population, climate change might worsen existing
regional disparities because it will reduce crop yields mostly in lands located at lower
latitudes where many developing countries are situated. Strategies to enhance local
adaptation capacity are therefore needed to minimize climatic impacts and to maintain
regional stability of food production. At the same time, agriculture as a sector offers
several opportunities to mitigate the portion of global greenhouse gas emissions that are
directly dependent upon land use, land-use change, and land-management techniques. This
paper reviews issues of agriculture and climate change, with special attention to adaptation
and mitigation. Specifically, as adaptation and mitigation strategies in agriculture are
implemented to alleviate the potential negative effects of climate change, key synergies
need to be identified, as mitigation practices may compete with modifications to local
agricultural practices aimed at maintaining production and income. Under future climate
and socio-economic pressures, land managers and farmers will be faced with challenges in
regard to selecting those mitigation and adaptation strategies that together meet food, fiber
and climate policy requirements.
Keywords Adaptation ! Agriculture ! Climate change impacts ! Mitigation !
Regional disparities ! Synergies ! Tradeoffs
C. Rosenzweig (&)
NASA Goddard Institute for Space Studies, New York, NY, USA
e-mail: crosenzweig@giss.nasa.gov
C. Rosenzweig ! F. N. Tubiello
Columbia University, New York, NY, USA
123
Mitig Adapt Strat Glob Change (2007) 12:855–873
DOI 10.1007/s11027-007-9103-8
1 Introduction
Climate change will affect the productivity of crop species and their geographic distri-
bution. Major contributing factors will include increasing atmospheric carbon dioxide,
rising temperature and a modified frequency of extreme events, possibly leading to more
drought and floods. These changes will in turn alter the availability of water resources,
productivity of grazing lands and livestock, and the distribution of agricultural pests and
diseases. Overall effects on cropping systems and farm activities will vary regionally.
Importantly, they will also depend on the specific management systems in use and their
adaptive capacities. Several studies suggest that recent warming trends in some regions
may already have discernible effects on agricultural systems (e.g., Nicholls 1997; Peng
et al. 2004).
The Intergovernmental Panel on Climate Change (IPCC 2000; 2001a) has attributed the
observed warming over the last century to anthropogenic forcing, i.e., the human-driven
emissions of greenhouse gases, chiefly carbon dioxide (CO
2
), methane (CH
4
), and nitrous
oxide (N
2
O) (IPCC 2001a ). Currently, the magnitude of observed warming is about 0.68C
over the last century, and mean global temperatures in the Northern hemisphere are higher
this century than they have been in the last 1,000 years (IPCC 2001a).
The ultimate significance of the climate change issue is related to its global reach,
affecting sectors and regions throughout the world in complex and interactive ways. In this
paper, we summarize recent studies projecting how climate change will affect agriculture
in the future, and focus on the potential roles of adaptation and mitigation strategies, and
their interactions, in responding to climate change.
2 Climate change and agriculture
A changing climate will affect agro-ecosystems in heterogeneous ways, with either benefits
or negative consequences dominating in different agricultural regions (Fig. 1). However,
the factors that prevail regionally may change over time, as gradual and possibly abrupt
climate changes develop in this century. Rising atmospheric CO
2
concentration, higher
temperature, changing patterns of precipitation, and altered frequencies of extreme events
will have significant effects on crop production, with associated consequences for water
resources and pest/disease distributions.
Fig. 1 Agro-ecosystem processes and a changing climate (from: Bongaarts 1994)
856 Mitig Adapt Strat Glob Change (2007) 12:855–873
123
2.1 Atmospheric carbon dioxide concentration
Many experiments show that crop yields increase on average by *30% for a doubling of
CO
2
concentration (Acock and Allen 1985; Cure and Acock 1986 ; Kimball 1983; Poorter
1993; Hsiao and Jackson 1999). Recent free-air CO
2
enrichment (FACE) experiments in
well-managed fields confirm these positive results (Hendrey et al. 1993; Kimball et al.
2002). Importantly, crop responses to elevated CO
2
have been shown to be modulated by
environmental and management factors. For instance, relative crop yield response to
elevated CO
2
, compared to ambient CO
2
levels, is greater in rain-fed than in irrigated
crops, due to a combination of increased water-use efficiency and root water-uptake
capacity (Tubiello and Ewert 2002). High-temperature and salinity stress may also increase
relative crop response, at least in the short term. Conversely, low fertilizer N applications
tend to depress crop responses to elevated CO
2
(Kimball and Idso 1983; Kimball et al.
2002).
It remains uncertain whether many of the effects of CO
2
enrichment observed in con-
trolled and FACE environments will prevail in farmers’ fields in the future. Under these
more typical conditions, many existing limiting factors––such as soil and water quality,
weed-crop competition, weed and pest interactions––as well as their unknown evolution
under elevated CO
2
and a changing climate might suppress the yield gains seen in current
experiments (e.g., Rosenzweig and Hillel 1998; Tubiello and Ewert 2002).
2.2 Temperature
Agricultural production may already have been affected by rising temperatures in recent
decades. For instance, Nicholls (1997) suggested that temperature trends in Australia were
responsible for 30–50% of observed recent gains in wheat yields, with increases in min-
imum temperatures and a related decrease in frost frequency the dominant influence.
Recently observed temperature increases may be extending crop-growing seasons in other
regions. Chmielewski et al. (2004) found that in Germany, for the period 1961–1990, the
beginning of the growing season advanced by 2.3 days per decade, following increases in
mean annual air temperature of 0.368C per decade. Over the same period, warmer tem-
peratures advanced the beginning of stem elongation in rye by 2.9 days per decade; the
beginning of cherry tree blossom by 2 days per decade; and the beginning of apple tree
blossom by 2.2 days per decade.
Rising temperatures may also be affecting yields in tropical regions. Peng et al. (2004),
analyzing 1979–2002 data from The Philippines, conclude that rice grain yields have
declined by about 15% for each 18C increase in growing-season mean temperature.
2.3 Climate variability, extreme events, and sea-level rise
Climate change may be characterized by an increase in climate variability (IPCC 2001a).
This may heighten the risks of crop failures, often connected to specific extreme events
during critical crop phases, such as heat waves or late frosts during flowering. In addition,
increases in temperature and precipitation variability will put pressure on crops grown on
their marginal climate ranges: for instance, increases in temperature variability in southern
wheat-growing areas may limit yields through lack of cold hardening and increased
winterkill.
Mitig Adapt Strat Glob Change (2007) 12:855–873 857
123
Precipitation extremes (i.e., droughts or floods) are also detrimental to crop produc-
tivity. Higher heavy precipitation and flooding regimes could increase crop damage in
some areas, due to soil water-logging, physical plant damage, and pest infestation (Ro-
senzweig et al. 2002a, b). At the opposite extreme, greater drought frequency and increased
evaporative demands may increase the need for irrigation in specific regions, further
straining competition for water with other sectors (Rosenzweig et al. 2004). In regions
lacking additional water resources, entire cropping systems may go out of production.
In coastal agricultural regions, sea-level rise and associated saltwater intrusion and
storm-surge flooding can harm crops through diminished soil aeration, salinization, and
direct damage. This is likely to be most serious in countries such as Egypt and Bangladesh,
with major crop-growing areas in low-lying coastal regions.
2.4 Agricultural pests
Under climate change, pests associated with specific crops may become more active
(Coakley et al. 1999; IPCC 1996). Increased use of agricultural chemicals might become
necessary, with consequent health, ecological, and economic costs (Rosenzweig et al.
2002a, b; Chen and McCarl 2001).
Higher temperatures may increase the growth of some weed species and extend their
geographic range towards higher latitudes (Dahlsten and Garcia 1989; Sutherst 1990). In
addition, warmer temperatures may speed development rates of some insect species;
resulting in shortened times between generations and improved capacity for over-wintering
at northern latitudes. Some insects populations may further become established and thrive
earlier in the growing season, during more vulnerable crop stages.
Current crop-pest interactions may change in response to elevated CO
2
. For instance,
due to differential responses of weeds and crops to CO
2
, some C
3
weeds may become more
invasive (Patterson 1993 ). Elevated CO
2
may also indirectly modify insect-crop relations,
via an increase in the C:N ratio in crop leaves, which renders them less nutritious per unit
mass. This would stimulate increased feeding by insects, leading to more plant damage
(Lincoln et al. 1984; Salt et al. 1995).
3 Global and regional predictions
Despite uncertainties about the rate and magnitude of climate change, recent assessment
studies have consistently shown that agricultural production systems in the mid and high
latitudes are likely to benefit in the near term (approximately to mid-century), while
production systems in the low-latitudes may decline over the coming few decades. Since
most of the developing countries are located in lower-latitude regions, increased diver-
gence in climate vulnerability between these groups of nations is expected (IPCC WG II
2001b). The combination of greater climate vulnerability and lower adaptive capacity may
create critical, additional challenges to developing countries as they confront global
warming in the coming decades. As shown in Table 1, these projections are confirmed by
simulation studies analyzing the consequences of global and regional climate impacts on
world food supply, in the context of concomitant socio-economic development over this
century (Parry et al. 2004; Rosenzweig and Parry 1994; IPCC 2001a, b, c).
If greenhouse gas emissions are not abated, crop production in more developed mid-
and high-latitude regions is also likely to decline towards the end of this century (Fig. 2).
858 Mitig Adapt Strat Glob Change (2007) 12:855–873
123
This is because the detrimental effects of increased heat and water stress on crop growth
will continue to progress as temperatures rise, while the beneficial effects of CO
2
on crop
yield will likely level out as CO
2
increases.
4 Response strategies
4.1 Adaptation strategies
Regardless of what local, regional and global actions are taken and which policy instru-
ments are adopted to slow anthropogenic emissions of greenhouse gases and thus to reduce
the magnitude of climate change, cumulative past emissions have already committed the
planet to a certain degree of climate change and associated impacts over the coming
decades. Climate actions taken today will determine how such changes will further evolve
in the second half of this century. Recent observations of increased frequency of climate
extremes worldwide, as well as shifts in eco-zones, might be an indication of global-
warming-related changes already under way (e.g., IPCC 2001a, b, c; Milly et al. 2002;
Root et al. 2003). Sectoral adaptation is thus very likely in the future and integral to the
study of climate change impacts on agriculture (IPCC 2001a, b, c; Smit and Skinner 2002;
Smith et al. 2003).
Table 1 Aggregated developing-developed country differences (per cent) in average crop yield changes
from baseline for the Hadley HadCM2 and HadCM3 climate change scenarios (Parry et al. 2004)
Scenario HadCM3—2080s HadCM2—2080s
A1F A2a A2b A2c B1a B2a B2b S550 S750
CO
2
(ppm) 810 709 709 709 527 561 561 498 577
World "500"1 "3 "1 "2 "11
Developed 3 8 6 7 3 6 5 5 7
Developing "7 "2 "2 "3 "4 "3 "5 "2 "1
Difference (%)
Developed-developing 10.4 9.8 8.4 10.2 7.0 8.7 9.3 6.6 7.7
Fig. 2 Generalized projection of world cereal production potential and areal extent under low and high CO
2
responses for increasing severity of climate change (data from Fischer et al. 2001)
Mitig Adapt Strat Glob Change (2007) 12:855–873 859
123
The key task at hand is to integrate findings and insights from the physical and social
sciences with local knowledge from farmers and land managers, in order to provide
guidance to decision-makers so as to promote robust sectoral strategies and appropriate
international cooperation. The aim is one of selecting strategies that, over a range of likely
future climate and socio-economic scenarios, minimize the potential negative impacts of
climate change while maximizing opportunities for adjustment.
Adaptation in agriculture is the norm rather than the exception. In addition to changes
driven by several socio-economic factors (chiefly market conditions and policy frame-
works), farmers always had to adapt to the vagaries of weather, on weekly, seasonal,
annual and longer timescales. The real issue in the coming decades will be the rate and
nature of climate change compared to the adaptation capacity of farmers. If future changes
are relatively smooth, farmers may successfully adapt to changing climates in the coming
decades by applying a variety of agronomic techniques that already work well under
current climates, such as adjusting the timing of planting and harvesting operations,
substituting cultivars, and––where necessary––modifying or changing altogether their
cropping systems.
Adaptation strategies will vary with agricultural systems, location, and scenarios of
climate change considered. For cereals, different adaptation strategies are needed for fall-
sown crops, such as winter wheat and barley, compared to spring crops, such as maize and
spring wheat. For example, a crop simulation study done as part of the U.S. National
Assessment (Tubiello et al. 2002) considered simple farm-level techniques, available to-
day, such as early planting––a realistic adaptation to climate change at many northern
agricultural sites––and the use of cultivars better adapted to warmer climates compared to
those currently grown at specific locations.
Early planting was simulated for spring crops to take advantage of changes in planting
windows caused by advances of last-frost dates, as well as to provide for heat and drought
stress avoidance in the late summer months. Growth and yield of better heat-adapted
cultivars were simulated for winter crops, such as winter wheat and barley, by testing
performance of cultivars with increased length of the grain-filling period. Under warmer
climates, crops would tend to mature faster, resulting in less time available for carbohy-
drate accumulation and grain production. By substituting current cultivars with ones
requiring longer time to mature, yield potential under climate change may be restored to
levels typical of current conditions. An additional adaptation strategy for winter-sown
cereals is the planting of cultivars having a reduced need for vernalization, i.e., the
requirements for set periods of cold temperatures during the vegetative stage of the crop to
induce bud formation in spring.
Responses to specific adaptation strategies for given cropping systems can still vary
considerably, as a function of location and climate scenario (Fig. 3). For instance, adapting
winter cereal production by using longer-maturing cultivars requires enough precipitation
over the extended growing season to sustain grain filling. If the particular climate scenario
considered consists of both warmer and drier conditions, such an adaptation strategy will
likely not work. Additionally, such a strategy might not work at southern sites, regardless
of the climate scenario considered, because farmers there already plant cultivars having
low vernalization requirements and maturity times in the upper range of those available. In
such cases, effective adaptation might not be possible without further breeding programs, a
process that typically takes a decade or longer before newly adapted cultivars can be
distributed to farmers. By the same token, Reilly et al. (2003) projected that early planting
could be a successful strategy for maize and spring wheat in the US Midwest, but not for
potato.
860 Mitig Adapt Strat Glob Change (2007) 12:855–873
123
In addition to changing planting strategies and cultivar type, land management systems
could be adapted to new climate conditions. Shifts from rainfed to irrigated agriculture is
the simplest such solution, although issues of water availability, cost, and competition from
other sectors need to be considered (i.e., Reilly et al. 2003; Tubiello et al. 2002; Rosen-
zweig et al. 2004). At higher levels of adaptation, cropping systems and crop types could
be changed altogether in addition to field management adjustments (i.e., Reilly et al. 2003),
or cultivation areas could shift geographically, following the creation of new agricultural
zonations determined by a changing climate (e.g., Fischer et al. 2001).
We note that our discussion on modeling adaptation is based primarily on agronomic
techniques that are either readily implemented by farmers today, or are likely to be readily
available in the coming decades, based on current knowledge. One advantage of this
approach is its specificity, since it can be easily communicated to and discussed with
stakeholders. The efficacy of such agronomic adaptation strategies under climate change in
a variety of production systems for given regions is easily tested within dynamic crop
models (e.g., Rosenzweig et al. 1995; Tubiello et al. 2002).
On the other hand, such an approach may be too farm-specific for assessment of more
aggregated levels of adaptation, involving, for example, regional planning for large-scale
changes in management and cropping systems that include sectoral competition for land
and water use or other market pressures. For these kinds of analyses, several authors have
used more economic-based approaches, allowing for qualitative-quantitative assessments
of higher levels of adaptation potentials, albeit with less agronomic detail (e.g., Polsky
2004; Adams et al. 1999; Easterling et al. 1993; Mendelsohn et al. 1994). These studies
tend to indicate small overall positive impacts for global agricultural economic indicators
across scenarios and models in the first half of this century, for climate changes at the
global scale of up to about 38C, and negative impacts above that degree of warming (see
e.g., Hitz and Smith 2004).
So far we have discussed adaptation strategies that might provide responses to climate
changes associated with smooth changes in mean variables, such as temperature and
precipitation regimes. What about climate variability? There are strong indications that
climate change will also bring about pronounced changes in climate variability (IPCC
2001a, b, c). Several studies have indicated that specific scenarios with mean warmer and
wetter conditions might be associated with increased frequency of heavy precipitation
events (i.e., Milly et al. 2002), with potential implications for increased crop losses. For
Fig. 3 Percent yield changes with and without adaptation under the Canadian. Climate Centre climate
change scenario in the 2030s: (left) spring wheat, with change of planting date; (right) winter wheat with
change of cultivar (Tubiello et al. 2002)
Mitig Adapt Strat Glob Change (2007) 12:855–873 861
123
example, Rosenzweig et al. (2002a, b) computed that agricultural losses in the U.S. due to
heavy precipitation and excess soil moisture could double by 2030.
As opposed to adaptation to changes in mean conditions, which require adjustments in
agronomic techniques (e.g., planting calendars, cultivar types, input amounts), adaptation
to future changes––likely an increase—in climate variability may require an attention to
stability and resilience of production, rather than to improving its absolute levels. Crop
management and cropping systems have evolved to provide farmers with stability of
production and thus steady income in the face of uncertain weather. The coefficient of
variation (CV) of yield in given areas may be used as a measure of system stability,
providing insight into superior cropping techniques at given sites. For example, continuous
winter wheat in Nebraska can have high CVs, over 50%, with high risk of complete crop
failure (as high as one in 5–10 years). Fallow practices that leave agricultural fields to rest
and accumulate moisture every other year, produce lower CVs (around 15%) and higher
long-term yields because of reductions in crop-failure probabilities. Cropping rotations,
integrated pest management, soil conservation and fallow techniques are all examples of
management practices that contribute to stability of farm production and income.
It is important to note that farming systems better adapted to local conditions are not
fully immune to risk, even under current conditions (witness the recurrent effects of
droughts and floods on various agricultural regions around the world). Hence it seems
unreasonable to expect perfect adaptation in the future to changing climate conditions.
Some adaptations will likely be successful (e.g., change in planting dates to avoid heat
stress), while other attempted adaptations (e.g., changing varieties and breeds, altered crop
rotations, development of new agricultural areas) may not always be effective in avoiding
the negative effects of droughts or floods on crop and livestock production. Importantly,
there are additional dimensions to adaptation, related to social and cultural aspects, that
might either favor or hinder adoption of new techniques by farmers, depending on com-
munity dynamics (Smith et al. 2003; Smit and Skinner 2002).
4.2 Mitigation strategies
While agriculture stands to be greatly affected by projected climate change, it also is, and
has been historically, a major source of greenhouse gases to the atmosphere, thus itself
contributing to climate change, possibly even from its inception. Clearing and management
of land for food and livestock production over the past century was responsible for
cumulative carbon emissions of about 150 GT C, compared to 300 GT C from fossil fuels
(LULUCF 2000). At present, agriculture and associated land use changes emit about a
quarter of the carbon dioxide (through deforestation and soil organic carbon depletion,
machine and fertilizer use), half of the methane (via livestock and rice cultivation), and
three-fourths of the nitrous oxide (through fertilizer applications and manure management)
annually released into the atmosphere by human activities.
Modifying current management of agricultural systems could therefore greatly help to
mitigate global anthropogenic emissions. Many see such activities in the coming decades
as new forms of environmental services to be provided to society by farmers, who in turn
could additionally increase their income by selling carbon-emission credits to other car-
bon-emitting sectors.
We focus this discussion on the agricultural carbon cycle, offering several entry points
for mitigation of greenhouse gas accumulation in the atmosphere. To this end, possible
mitigation approaches in agriculture concentrate on either (or both) of two key
862 Mitig Adapt Strat Glob Change (2007) 12:855–873
123
components: (1) Sequestration of atmospheric C in agricultural soils, resulting in increased
soil organic carbon (SOC) pools; and (2) Reduction of greenhouse gas emissions to the
atmosphere from agricultural operations. An important difference among the two options
above is that soil carbon sequestration is ultimately finite (Lal et al. 1999): positive
manipulations in soil management will tend to increase the equilibrium soil carbon pool by
increasing C inputs into the soil or by slowing decay rates of soil organic matter, but SOC
accumulation will not proceed above the resulting new storage point. By contrast, man-
agement changes that reduce carbon fluxes from agricultural operations can last indefi-
nitely, as long as the new management system is sustainable in both energy and ecological
terms (Schlesinger 1999).
4.2.1 Carbon sequestration
Of the 150 GT C that were lost in the last century due to land conversion to agriculture and
subsequent production, about two thirds were lost due to deforestation and one-third,
roughly 50 GTC, due to cultivation of current agricultural soils and exports as food
products (LULUCF 2000). The latter figure thus represents the maximum theoretical
amount of carbon that could be restored in agricultural soils. In practice, as long as 40–50%
of total above-ground grain or fruit production is exported as food to non-agricultural
areas, the actual carbon amount that can be restored in agricultural soils is much lower.
Efforts to improve soil quality and raise SOC levels can be grouped into two sets of
practices: crop management and conservation tillage. Both practices evolved as means to
enhance sustainability and resilience of agricultural systems, rather than with SOC
sequestration in mind. They include so-called ‘‘best practice’’ agricultural techniques, such
as use of cover crops and/or nitrogen fixers in rotation cycles; judicious use of fertilizers
and organic amendments; soil water management improvements to irrigation and drainage;
and improved varieties with high biomass production. Tables 2 and 3 summarize potentials
for C-sequestration for a variety of agronomic field techniques.
By combining this information with current and future agricultural land use, including
levels of technology projected by IPCC and FAO (LULUCF 2000; Fischer et al. 2001), we
can make a first-order estimate of total future contributions to soil carbon storage from
agricultural practices over existing agricultural and marginal lands. Table 4 shows that,
Table 2 Estimated carbon sequestration rates for different ‘‘good practice’’ management practices
Practice Country/region C gain (T C ha
"1
yr
"1
) Time (years)
Improved crop production and erosion control Global 0.05–0.76 25
Partial elimination of bare fallow Canada 0.17–0.76 15–25
USA 0.25–0.37 8
Irrigation USA 0.1–0.3
Fertilization USA 0.1–0.3
Yield increase, reduced bare fallow China 0.02 10
Amendments Europe 0.2–1.0 50–100
Forages in rotation Norway 0.3 37
Ley-arable farming Europe 0.54 100
Source: LULUCF (2000), IPCC ( 2000a)
Mitig Adapt Strat Glob Change (2007) 12:855–873 863
123
over the next 40 years, best practice and conservation tillage alone could store about
8 GT C in agricultural soils. Larger amounts could be sequestered over the same period by
increasing C inputs into land, for instance by establishing agro-forestry practices in mar-
ginal lands (20 GT C), or by reducing disturbance, such as by conversion of excess
agricultural land to grassland (3 GT C). The total gain from multiple mitigation approaches
over existing agricultural land would thus be roughly 10 GT C (and up to 30 GT C with the
inclusion of marginal land conversion for agro-forestry), an amount lower than the
50 GT C lost historically.
An important caveat to the implementation of best practice and reduced tillage agri-
culture as a means to enhance SOC sequestration is that C emitted from the manufacture
and use of additional agricultural inputs may negate all or part of the increased C
sequestered by soils (Schlesinger 1999). Under current practices, the fossil fuel that powers
the machinery to sow, irrigate, harvest, and dry crops worldwide, and including fertilizer
manufacture, is already responsible for atmospheric emissions of about 150–
200 MT C yr
"1
. Given that total cropland covers about 1.5 G ha of global ice-free land, this
figure corresponds to a world average emission rate of 100–130 kg C ha
"1
yr
"1
.
In order to assess fully the net C effects of a mitigation practice, it is necessary to
analyze the full C cycle of a given agricultural system. For example, a recent study (West
and Marland 2002) analyzed the full C cycle for intensive agriculture in the US Midwest
(corn, wheat, and soybean rotation systems) and found that reduced-tillage agriculture was
superior to conventional tillage (CT), not only in terms of its direct benefits (C stored in
soil of 330 kg C ha
"1
yr
"1
compared to zero in CT), but also in terms of indirect effects,
resulting in reduced C emissions from reduced requirements for field operations and inputs
(137 kg C ha
"1
yr
"1
in reduced tillage versus 178 kg C ha
"1
yr
"1
in CT). The latter
indirect reductions were accomplished in spite of increased input use (mainly pesticides
and herbicides), because machinery and labor for soil preparation were much lower in the
reduced-tillage systems.
Table 3 Estimated carbon
sequestration rates under reduced
or no tillage practices, as reported
in various countries
Source: LULUCF (2000), IPCC
(2000a)
Country/region C gain (T C ha
"1
yr
"1
) Time (years)
Global 0.1–1.3 25
UK 0.15 5–10
Australia 0.3 10–13
USA 0.3 6–20
Canada 0.2 8–12
USA and Canada 0.2–0.4 20
Europe 0.34 50–100
Southern USA 0.5 10
Table 4 Estimated carbon
sequestration over the next
40 years, as a function of land use
management of existing cultivated
and marginal land. Data
elaborated from regional and
temporal data in LULUCF (2000),
IPCC (2000)
Sector Total Gt C sequestered
‘‘Best Practice’’ Crop management 8
Agroforesty improvements 1.6
Cropland conversion to agroforesty 19.5
Cropland conversion to grassland 2.4
Total arable land 31.5
864 Mitig Adapt Strat Glob Change (2007) 12:855–873
123
4.2.2 On-farm reduction of greenhouse gas emissions
In general, the direct benefits of carbon sequestration in reduced tillage systems are limited
in time, typically 20–40 years, while those arising from reduced C emissions will last as
long as the relative management changes are maintained. Therefore, even when such flux
reductions appear small compared to total anthropogenic emissions, they may contribute
substantially to mitigate sectoral emissions. In the case of US agriculture for example, the
estimates by West and Marland (2002) suggest that reduced tillage practices could con-
tribute to making US agriculture ‘carbon neutral’ over the next 40 years. If they were
extended to the 200 M ha of total US cropland, they could sequester and/or reduce overall
carbon emissions in agriculture by about 40–50 MT C yr
"1
. These estimates, in agreement
with previous studies (i.e., Lal et al. 1999; Sperow et al. 2003), are of the same order of
magnitude of estimated C emissions from US agriculture (see e.g., CAST 2004).
In another entry point to the carbon cycle, agriculture may help to mitigate anthropo-
genic greenhouse emissions through the production of bio-fuels. If available marginal land
were used for energy crops, the IPCC projects significant displacement of fossil fuels,
globally up to 3–4 GT C yr
"1
by mid century through conversion of *200 M ha of
marginal land to bio-fuel production (IPCC 2001c). However, issues of input availability,
especially water, have not been considered in previous studies and need to be further
investigated.
Because of the greater global warming potential (GWP) of CH
4
(21) and N
2
O (310)
compared to CO
2
(1), mitigation of non-CO
2
greenhouse gases in agriculture, can be quite
significant and achieved via the development of more efficient rice (for methane) and
livestock production systems (for both methane and nitrous-dioxide). In intensive agri-
cultural systems with crops and livestock production, direct CO
2
emissions are predomi-
nantly connected to field crop production and are typically in the range of 150–
200 kg C kg C ha
"1
yr
"1
(e.g., West and Marland 2002; Flessa et al. 2002). Recent full
greenhouse gas analyses of different farm systems in Europe showed that such CO
2
emissions represent only 10–15% of the farm total, with methane contributing 25–30% and
N
2
O, by far the largest emitter, contributing roughly 60% of total greenhouse gas emissions
from farm activities. The N
2
O contribution arises from substantial N volatilization from
fertilized fields and animal waste, but it is also a consequence of its very high GWP.
In Europe, methane emissions are mostly linked to cattle digestive pathways; its con-
tribution also dominates that of CO
2
, due in part to methane’s high GWP. Mitigation
measures for methane production in livestock include improved feed and nutrition regimes,
as well as recovery of bio-gas for on-farm energy production. Strategies for effective
mitigation of N
2
O emissions are far more difficult, given the largely heterogeneous nature
of emissions in space and time and thus the difficulty of timing fertilizer applications and/
or manure management. Large uncertainties in emission factors also complicate the
assessment of efficient N
2
O-reduction strategies. Current techniques focus on reduction of
absolute amounts of fertilizer N applied to fields, as well as on livestock feeding regimes
that reduce animal excreta.
By analyzing all components of farm activities, Flessa et al. (2002) suggested that
overall emissions of the non-CO
2
gases could be reduced by about 25% by shifting to less
intensive, organic production systems. Given the higher GWP of both CH
4
and N
2
O
compared to that of CO
2
however, overall farm emissions could still be significant even in
organic systems. A possibly viable strategy to mitigating non-CO
2
gases in intensive mixed
crop-livestock farming systems, such as those in place in both Europe and North America,
Mitig Adapt Strat Glob Change (2007) 12:855–873 865
123
might be a change in human diet towards less meat consumption, thus reducing livestock
numbers, as well as grain production for feed (Flessa et al. 2002).
4.3 Interactions of adaptation and mitigation strategies
Agriculture plays a fundamental, dual role in human-driven climate change. On the one
hand, it is one the key human sectors that will be affected by climate change over the
coming decades, thus requiring adaptation measures. On the other, agriculture is also a
major source of greenhouse gases to the atmosphere. As climate changes as well as socio-
economic pressures shape future demands for food, fiber and energy, synergies need to be
identified between adaptation and mitigation strategies, so that robust options that meet
both climate and societal challenges of the coming decades can be developed. Ultimately,
farmers and others in the agricultural sector will be faced with the dual task of contributing
to global reductions of carbon dioxide and other greenhouse gas emissions, while having to
cope with an already changing climate.
First, one should consider interactions between adaptation strategies, which will cer-
tainly be implemented by farmers as climate changes, and the mitigation potential of the
adapted system. Some very specific adaptation practices might not be conducive to miti-
gation at all. If, for example, agricultural zonation shifts the earth’s potential agricultural
limits polewards, increased cultivation in those previously marginal areas––certainly seen
as a boon by certain countries, might on the other hand lead to substantial losses of SOC in
previously undisturbed lands. The same might be true under major shifts in rotation sys-
tems with very different production levels, occurring across regions over large areas.
In terms of livestock production in intensive systems, warmer conditions in the coming
decades might trigger the implementation of enhanced cooling and ventilation systems, or
alternatively it may render necessary a reduction in stocking densities (Turnpenny et al.
2001). The former of such strategies would clearly counter on-farms mitigation efforts due
to the associated increase in energy use, while the latter would greatly contribute to
mitigation of non-CO
2
greenhouse gases.
On the other hand, on the majority of current agricultural areas several adaptation
practices may positively reinforce land mitigation potentials under specific conditions. For
example, increased irrigation and fertilization necessary to maintain production in mar-
ginal semi-arid regions under climate change conditions, may also greatly enhance the
ability of soils in those areas to sequester carbon. This would be especially true in sub-
Saharan Africa, where small improvements in efficiency of irrigation can have very large
effects on biomass production of crops (Solomon et al. 2000), and hence on their soil
inputs. Under wet scenarios especially at mid-latitudes, a shift from fallow systems to
continuous cultivation––an adaptation maximizing production under the new precipitation
conditions––would also increase soil carbon sequestration potentials.
The interactions of mitigation potential with climate change itself need to be consid-
ered. Climate change impacts on agriculture will affect not only yields, but also SOC levels
in agricultural soils. Such impacts can be either positive or negative, depending on the
particular effect considered. Elevated CO
2
alone will have positive effects on soil carbon
storage, because increased above and belowground biomass production in the agro-eco-
system. Likewise, the lengthening of the growing season under warmer climates will allow
for increased carbon inputs into soils. Warmer temperatures may also have negative effects
on SOC however, by increasing decomposition rates as well as by reducing inputs by
shortening crop life cycles.
866 Mitig Adapt Strat Glob Change (2007) 12:855–873
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Increased variability and higher frequency of extreme events will negatively impact soil
carbon storage, by both decreasing locally mean production levels, as well as by worsening
soil quality in the areas affected. Paustian et al. (1998) simulated several cropping systems
in the US Midwest under current and future projected climate, showing ––in agreement
with crop production assessment studies––both positive and negative results, varying
regionally and as a function of climate scenarios used.
If changing climate is not taken into consideration, calculations of soil carbon
sequestration potentials may be in serious error because of the interactions between climate
and soil dynamics, As a result, mitigation strategies chosen today at given sites, without
attention to likely changes in climate, may not produce the expected results.
For example, consider how climate change might modify the potential impacts of
enhanced field input management for water and fertilizer N. By using a dynamic crop
modeling system coupled to a soil carbon module (DSSAT; see for example Gijsman et al.
2002), we computed differences in SOC sequestration at a US Midwest site, following
increased N and water application As shown in Fig. 4, while such mitigation strategies are
projected to produce numbers that are consistent with those discussed in our section on
mitigation, results may change substantially once climate change is taken into consider-
ation. In our example, increased fertilization and/or irrigation management is projected to
lead to additional SOC sequestration of about 0.1 T C ha
"1
yr
"1
under current climate, in
agreement with published estimates of mitigation potentials in agriculture. However,
compared to the same baseline, climate change might entirely negate or sharply reduce
such gains in the future. In addition, different climate scenarios will have different effects
on final accumulation rates.
Interactions between mitigation strategies and adaptation measures may be important,
although they are often overlooked. If the main avenue chosen for mitigation options
related to soil carbon sequestration would be conversion of marginal agricultural lands to
forestry, agro-forestry, grasslands, or bio-energy crops, competition for land and food
would need to be considered as a function of specific socio-economic scenarios. Fischer
et al. (2001) projected future extent of agricultural land as a function of SRES scenarios
(IPCC 2000), showing a need for additional agricultural land on the order of 200–
400 M ha, mostly in Latin America and sub-Saharan Africa, under the scenario with the
highest projected population and lower economic growth. Under the latter circumstances,
very little additional marginal land would be available for mitigation purposes.
On current agricultural land however, interactions between mitigation and adaptation
can be mutually re-enforcing, especially in view of increased climate variability under
Fig. 4 Change in soil carbon in corn production under nitrogen fertilization and irrigation under current
climate and under the Canadian Climate Centre, (CCCM) and Hadley Center (HAD) climate change
scenarios. Simulated data provided by NASA-GISS climate impacts group
Mitig Adapt Strat Glob Change (2007) 12:855–873 867
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climate change. This is because, most mitigation techniques currently considered in
agriculture, including reduced tillage, were originally designed as ‘‘best practice’’ man-
agement strategies, aimed at enhancing the long-term stability and resilience of cropping
systems in the face of climate variability or of increased cultivation intensity. By
increasing the ability of soils to hold soil moisture and to better withstand erosion, and by
enriching ecosystem biodiversity through the establishment of more diversified cropping
systems, many mitigation techniques implemented locally for soil carbon sequestration
may also help cropping systems to better withstand droughts and/or floods, both of which
are projected to increase in frequency and severity in future warmer climates.
5 Research directions
In order to better address the interactions between climate change, adaptation, mitigation,
and sustainability of food and fiber production, we suggest the following areas for future
research.
5.1 Climate variability and change
A bifurcation in the field of climate impacts has occurred between research on responses to
major systems of climate variability, such the El Nin
˜
o-Southern Oscillation, and responses
to long-term global warming. The insights gained with regard to adaptation and mitigation
on these two timescales––seasonal-to-interannual versus decadal-to-century––need to be
reconciled. The work on seasonal-to-interannual climate forecasts has tended to focus on
short-term decision-making following probabilistic predictions of climate extremes in
connection with El Nin
˜
o and La Nin
˜
a events (Fig. 5). The role of local stakeholders is
crucial at these shorter timescales, and responses are focused on adaptation. The work on
the decadal-to-century timescale, on the other hand, has focused primarily on responses to
mean changes and long-term decisions. The stakeholders for climate change impact studies
have often been national policy-makers. The goal here has usually been to provide
Fig. 5 Normalized vegetative index (NDVI) for Uruguay, showing wet periods during El Nino events (e.g.,
February 1998) and droughts during La Nina events (e.g., February 2000)
868 Mitig Adapt Strat Glob Change (2007) 12:855–873
123
information needed to help these decision-makers to devise long-term strategies in regard
to the climate change issue, in terms of both mitigation and adaptation.
New theoretical constructs are needed to link climate-agriculture interactions on the two
timescales, as well as new ways to utilize analytic tools such as dynamic crop growth
models and statistical analyses. One need is to move beyond the readily tractable pro-
jections of crop responses to mean changes, towards the more difficult yet highly relevant
issue of how crops may respond to altered climate variability, such as changes in the
frequency and intensity of extreme events.
5.2 Observed effects of warming trends
Analyses of temperature records from around the world show that many regions are
experiencing a warming trend, especially from the 1970s to the present. On average,
warmer-than-normal springs have been documented in western North America since the
late 1970s (Cayan et al. 2001). In some areas of the world, there have also been recent
episodic increases in floods (e.g., North America) and droughts (e.g., the Sahel) (IPCC
2001a, b, c), with likely but as yet mostly undocumented effects on food production. The
responses of agricultural systems to such changes need to be monitored and documented in
regard to impacts and adaptation. Have farmers indeed switched to earlier planting dates?
Have they changed cultivars? And are there any trends in yields that can be discerned in
conjunction with the climate trends?
Such questions are difficult to answer because many other processes besides climate,
including land-use change and agro-ecosystem degradation, have been occurring simul-
taneously. But such questions are important for furthering our understanding of agricultural
adaptation to climate, and for validating the many simulation studies performed to date on
potential climate change impacts over the coming decades. These analyses will contribute
to the IPCC Fourth Assessment Report, now underway.
5.3 Global and local scales
An important bifurcation that needs to be resolved is the one between global and local/
regional scales. Recent work has emphasized the importance of scale in estimating the
impacts of climate variability and change on agriculture (Mearns 2003). In order to
understand how a changing climate will affect agriculture, we must find new ways to bring
detailed knowledge on impacts and adaptation at local and regional scales to bear on global
analyses.
Agriculture in any one region is linked to other agricultural regions, and indeed to the
world food system, both through trade and through the food-donor system. As a changing
climate shifts the comparative advantage of one region over another, additional regions
will inevitably be affected. Thus, in research on agriculture and climate change, regional
‘place-based’ studies of vulnerability and adaptation, as well as mitigation, can contribute
to a global synthesis.
5.4 Mitigation and agriculture-forestry competition
An emerging research area is related to the potential for competition between agriculture
and forestry in regard to carbon-saving solutions. What are optimal strategies for land
Mitig Adapt Strat Glob Change (2007) 12:855–873 869
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management leading to climate mitigation? For example, might carbon sequestration on
agricultural land used for food production be ‘out-competed’ by biomass production for
energy on the same fields? Might agro-forestry storage for carbon become more lucrative
than cereal production? Several studies have started to analyze such interactions (e.g.,
Hyman et al. 2003; McCarl et al. 2001), including quantification of C-sequestration,
secondary effects on impacts and the environment, and other pollutants such as tropo-
spheric ozone (e.g., Rosenzweig et al. 1999; Feltzer et al. 2004). If a main avenue chosen
for agricultural mitigation of greenhouse gas concentrations is conversion of marginal
agricultural lands to forestry, agro-forestry, grasslands, or bio-energy crops, competition
between these different carbon-sequestration techniques may ensue. Projections of land
resources required for GHG mitigation and for food production need to be made as a
function of specific socio-economic scenarios. These will be part of interdisciplinary
studies that entrain agronomists, forestry scientists, and economists in order to develop full
carbon and food accounting for agricultural systems over sufficiently long time periods in
the future to capture the complex interactions among these processes.
6 Conclusions
Climate change and variability will affect agricultural systems substantially, requiring
farmers to adapt at the same time that they are called on to reduce emissions at the farm
level. Choosing effective adaptation and mitigation strategies will represent a key chal-
lenge for farmers over the coming decades. Optimal strategies are those that, via careful
management of land, maintain or increase the resilience and stability of production sys-
tems, while also sequestering soil carbon and/or reducing fluxes from farm activities.
Although many positive interactions have been identified in this essay, it is important to
note that synergies will not be possible under all climate and socio-economic scenarios,
and across regions. Adaptation strategies will likely often take precedence over mitigation,
as climate changes are already under way and farmers will adapt (as they have always
done), in order to maintain production systems and thus their own incomes and livelihoods.
Certainly, over the coming decades, the global and regional challenges connected to
anthropogenic climate forcing call for the need to maximize collaboration among scien-
tists, farmers and land managers, politicians, and citizens, in order to ensure efficient
responses to a global problem that is in essence interconnected across years, regions, and
societal sectors.
Finally, improving responses to climate variability and change is a crucial requirement
for future agricultural sustainability. The challenge for the field of climate change impacts
on agriculture, including the design of appropriate adaptation and mitigation solutions, is to
integrate insights from the physical, biophysical, and social sciences into a comprehensive
understanding of climate-agriculture interactions at seasonal-to-interannual and decadal-to-
century timescales, as well as at regional and global spatial scales. The ultimate challenge
is to apply this knowledge to ‘real-world’ agricultural practices and planning worldwide, so
that long-term sustainability may be effectively enhanced under climate change, by finding
the optimal synergies between the necessary adaptation and mitigation strategies.
Acknowledgements We wish to thank three anonymous reviewers for their constructive comments, which
helped us to improve the overall structure and clarity of the manuscript. The research was supported in part
by a grant of the Italian Ministry of the Environmentadministered by INGV Bologna. F. N. Tubiello was
supported in part by NOAA grant GC02–333.
870 Mitig Adapt Strat Glob Change (2007) 12:855–873
123
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