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Acknowledgments: We thank all members of the Moritz lab
for their helpful comments and suggestions. C.M.’s research
relating to climate change effects has been supported by
the National Science Foundation (the Australian Research
Council) and the Gordon and Betty Moore Foundation. R.A.
is funded by a Spanish postdoctoral fellowship financed by
the Ramon Areces Foundation (www.fundacionareces.es/
fundacionareces/).
10.1126/science.1237190
REVIEW
Climate Change Impacts
on Global Food Security
Tim Wheeler1,2* and Joachim von Braun3
Climate change could potentially interrupt progress toward a world without hunger. A robust and
coherent global pattern is discernible of the impacts of climate change on crop productivity that could
have consequences for food availability. The stability of whole food systems may be at risk under
climate change because of short-term variability in supply. However, the potential impact is less clear at
regional scales, but it is likely that climate variability and change will exacerbate food insecurity in
areas currently vulnerable to hunger and undernutrition. Likewise, it can be anticipated that food access
and utilization will be affected indirectly via collateral effects on household and individual incomes, and
food utilization could be impaired by loss of access to drinking water and damage to health. The
evidence supports the need for considerable investment in adaptation and mitigation actions toward a
“climate-smart food system” that is more resilient to climate change influences on food security.
Tackling hunger is one of the greatest challenges
of our time (1). Hunger has multiple
dimensions and causes, ranging from
deficiencies in macro- and micro-nutrients, through
short-term shocks on food access, to chronic shortages.
Causes range from constraints on the supply
of food of sufficient quantity and quality and lack
of purchasing power to complex interactions of
nutrition with sanitation and infectious diseases
leading to poor health. Several of these causes
have been addressed in recent decades, and substantial
progress has been made in reducing the
proportion of the world’s undernourished population
from an estimated 980 million in 1990–92
to about 850 million in 2010–12 (2). However,
from other relevant indicators of nutrition, such
as child underweight and stunting and health surveys,
an estimated 2 billion people still suffer
from micro-nutrient deficiencies today.
The long-term reduction in the prevalence of
undernutrition worldwide has slowed since 2007,
as a result of pressures on food prices, economic
1
Walker Institute for Climate System Research, Department
of Agriculture, University of Reading, Reading RG6 6AR, UK.
2
Department for International Development, 22-26 Whitehall,
London SW1A 2EG, UK. 3
ZEF B: Center for Development Research,
Department of Economic and Technical Change, University
of Bonn, Walter-Flex-Strasse 3 53113 Bonn, Germany.
*Corresponding author. E-mail: t.r.wheeler@reading.ac.uk
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volatilities, extreme climatic events, and changes
in diet, among other factors. Furthermore, additional
pressures on the global food system are
expected to build in the future. For example, demand
for agricultural products is estimated to
increase by about 50% by 2030 as the global population
increases (3), which will require a shift
toward sustainable intensification of food systems
(4). The impacts of climate change will have many
effects on the global food equation, both for supply
and demand, and on food systems at local
levels where small farm communities often depend
on local and their own production (5). Thus, climate
change could potentially slow down or reverse
progress toward a world without hunger.
Here, we offer an overview of the evidence for
how climate change could affect global food security,
with particular emphasis on the poorer parts
of the world. We deliberately take a broad view of
the complex interactions between climate change
and global food security, stating what we do know
with some degree of confidence, as well as acknowledging
aspects where there is little or no evidence.
We end by proposing a number of precepts
for those making policy or practical decisions
on climate change impacts and food security.
Food Security
Together, climate change and food security have
multiple interrelated risks and uncertainties for
societies and ecologies. The complexity of global
food security is illustrated by the United Nations’
Food and Agricultural Organization (FAO) (6)
definition: (i) the availability of sufficient quantities
of food of appropriate quality, supplied through
domestic production or imports; (ii) access by individuals
to adequate resources (entitlements) for
acquiring appropriate foods for a nutritious diet;
(iii) utilization of food through adequate diet,
clean water, sanitation, and health care to reach a
state of nutritional well-being where all physiological
needs are met; and (iv) stability, because
to be food secure, a population, household or individual
must have access to adequate food at all
times.
It is extremely challenging to assess precisely
the current status of global food security from
such a broad concept. However, the big picture
is clear: About 2 billion of the global population
of over 7 billion are food insecure because they
fall short of one or several of FAO’s dimensions
of food security. Enormous geographic differences
in the prevalence of hunger exist within
this global estimate, with almost all countries in
the most extreme “alarming” category situated
in sub-Saharan Africa or South Asia (7) (Fig. 1).
Nevertheless, it is important to note that the
current numbers for undernourished people are
rough estimates at best and are seriously deficient
in capturing the access, utilization, and
stability dimensions of food security. First, the
methods used to make these estimates only capture
longer-term trends, not the short-term changes
that can be an important consequence of climate
variability. The most recent data are averages for
the period 2010–2012 (2), so they do not capture
a specific year, let alone shorter-term shocks,
be they climate-related or otherwise. Second, they
estimate calorie shortage only and do not cover
other dietary deficiencies and related health effects
that can impair physical and mental capacities.
Third, they are derived from aggregate data,
not actual household or individual-level food deficiencies,
which hinders analyses of distributional
effects of climate and other shocks. The
FAO methodology was recently improved (8), but
the above shortcomings could not be addressed
within the framework of the current method, and
thus, current analyses of climate change impacts
on food security are incomplete. An overhaul of
data-gathering methods that encompasses food
deficiencies at household levels, as well as nutritional
status, is needed.
Climate Change
There is a substantial body of evidence that
shows that Earth has warmed since the middle
of the 19th century (9–14). Global mean temperature
has risen by 0.8°C since the 1850s, with
the warming trend seen in three independent temperature
records taken over land and seas and in
ocean surface water (15). Climate change can
result from natural causes, from human activities
Fig. 1. Global distribution of hunger as quantified by the 2012 Global
Hunger Index. The Welthungerhilfe, IFPRI, and Concern Worldwide Hunger map 2012
calculated a Global Hunger Index (7) for 120 countries by using the proportion of
people who are undernourished, the proportion of children under 5 who are underweight,
and the mortality rate of children younger than age 5, weighted equally.
[Reproduced with permission from Welthungerhilfe, IFPRI, and Concern Worldwide (7)]
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through the emission of greenhouse gases such as
carbon dioxide and methane, and from changes
in land use. Carbon dioxide (CO2) levels in the
atmosphere have increased from about 284 ppm
in 1832 to 397 ppm in 2013 (16), and there is a
theoretical link between the levels of such “greenhouse”
gases in the atmosphere and global warming.
Three independent reviews have found strong
evidence for human causes for the observed temperature
warming mainly caused by the burning
of fossil fuels, with smaller contributions from
land-use changes (15–18).
Thus, climate change is expected to bring
warmer temperatures; changes to rainfall patterns;
and increased frequency, and perhaps severity,
of extreme weather. By the end of this
century, the global mean temperature could be
1.8° to 4.0°C warmer than at the end of the previous
century (15). Warming will not be even
across the globe and is likely to be greater over
land compared with oceans, toward the poles,
and in arid regions (15). Recent weather records
also show that land surface temperatures may be
increasing more slowly than expected from climate
models, potentially because of a higher
level of absorption of CO2 by deep oceans (19).
Sea-level rises will increase the risk of flooding
of agricultural land in coastal regions. Changes in
rainfall patterns, particularly over tropical land,
are less certain, partly because of the inability of
the current models to represent the global hydrological
cycle accurately (20). In general, it is
expected that the summer Asian monsoon rainfall
may increase, while parts of North and southern
Africa could become drier (15). How will these
regional changes in climate affect food security?
Research Biases
Agriculture is inherently sensitive to climate variability
and change, as a result of either natural
causes or human activities. Climate change caused
by emissions of greenhouse gases is expected to
directly influence crop production systems for food,
feed, or fodder; to affect livestock health; and to
alter the pattern and balance of trade of food and
food products. These impacts will vary with the
degree of warming and associated changes in rainfall
patterns, as well as from one location to another.
Climate change could have a range of direct and
indirect effects on all four dimensions of food security.
How is the evidence base distributed across the
dimensions of food security? We undertook a bibliographic
analysis of peer-reviewed journal papers
on food security and climate change since the publication
of the first Intergovernmental Panel on Climate
Change (IPCC) report in 1990 (21). That
report was ground-breaking for the climate science
that it reviewed, but agriculture was entirely absent.
Our analysis shows that a small peak of papers with
climate change and food security in the title or
abstract were published in the mid-1990s, followed
by a lull then a sharp increase in papers published
with these terms from 2008 onward.
The distribution of the evidence across the four
dimensions of food security is, however, heavily
skewed toward food availability within 70% of the
publications. Access, utilization, and stability dimensions
of food security are represented by only
11.9, 13.9, and 4.2% of the total publications on
food security and climate change, respectively.
Why is the evidence based on climate change
impacts so unevenly distributed across the four
dimensions of food security? There are several
possibilities. Research has largely concentrated
on the direct effects of climate change, such as
those on crop growth and on the distribution of
agricultural pests and diseases. Also, studies
have understandably focused on areas that can
be easily investigated, often through analyzing
single-factor changes, and have avoided the complex
and multilayered features of food security
that require integrations of biophysical, economic,
and social factors. Clearly, current knowledge
of food security impacts of climate change is dramatically
lacking in coverage across all dimensions
of food security. Nevertheless, where there
is good evidence, what are the broad conclusions?
Food Availability
Rosenzweig and Parry (22) produced the first
global assessment of the potential impacts of
climate change scenarios on crops. They used
numerical crop models of wheat, rice, maize,
and soybeans to simulate yields at 112 locations
in 18 countries, in the current climate and under
climate change using the output of three climate
models. These point-based estimates of change
Fig. 2. Global impacts of climate change on crop productivity from simulations published in
1994 and 2010. (Top) The 1994 study (22) used output from the GISS GCM (in this example) with twice
the baseline atmospheric CO2 equivalent concentrations as input to crop models for wheat, maize,
soybean, and rice that were run at 112 sites in 18 countries. Crop model outputs were aggregated to a
national level using production statistics. (Bottom) The 2010 study (27) simulated changes in yields of 11
crops for the year 2050, averaged across three greenhouse emission scenarios and five GCMs. [Reprinted
by permission from (top) Macmillan Publishers Ltd. (22); (bottom) World Bank Publishers (27)]
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were then scaled-up to country level by using
national crop production statistics. Future climate
simulations under both present-day and doubledCO2
concentrations were used. They found that
enhanced concentrations of atmospheric CO2 increase
the productivity of most crops through
increasing the rate of leaf photosynthesis and
improving the efficiency of water use. However,
more recent research has proposed that the CO2
yield enhancement in crop models is too large
compared with observations of crop experiments
under field conditions (23). If true, these revised
estimates will affect the magnitude of the previous
global crop yield changes but not the
spatial distribution of impacts. Even if there is
some debate on the magnitude of CO2 effects,
higher concentrations of CO2 in the atmosphere
are already having noticeable continental level
effects on plant growth in sub-Saharan Africa (24).
The simulations of Rosenzweig and Parry (22)
showed that there is a large degree of spatial variation
in crop yields across the globe. Both the sign
and magnitude of the projected changes in crop
yield vary with alternative climate models and from
one country to another. In general, yields increased
in Northern Europe, but decreased across Africa
and South America (22) (Fig. 2). Inevitably, there
were methodological weaknesses in this study,
including the use of only just over one hundred
points to represent global crop production, the
absence of any change in the areas suitable for
crop production in future climates, limitations on
how each of the model points is representative of
their surrounding regions, and assumptions about
varieties in the crop model parameters themselves.
Nevertheless, as the first example of global impacts
of climate change on crop production, these
simulations are remarkable.
Since 1994, knowledge of the effects of climate
on crop plant physiology has improved,
the skill of simulation methods for climate change
impact studies has increased, and better computing
power and data sets to run global simulations
have become available. Landmark studies
since 1994 include those by Parry and colleagues
(25), Cline (26), and, most recently, the World
Bank (27) (Fig. 2). Specific projections vary with
the climate model scenario used, the simulations
methods, and the time scale over which the projections
are done. However, the broad-scale pattern
of climate change impacts on crop productivity
and production has remained consistent across
all of these global studies spanning almost
20 years of research. Crop yields are more negatively
affected across most tropical areas than at
higher latitudes, and impacts become more severe
with an increasing degree of climate change.
Furthermore, large parts of the world where crop
productivity is expected to decline under climate
change (Fig. 2) coincide with countries that currently
have a high burden of hunger (Fig. 1). We
conclude that there is a robust and coherent pattern
on a global scale of the impacts of climate change
on crop productivity and, hence, on food availability
and that climate change will exacerbate food
insecurity in areas that already currently have a
high prevalence of hunger and undernutrition.
A recent systematic review of changes in the
yields of the major crops grown across Africa
and South Asia under climate change found that
average crop yields may decline across both
regions by 8% by the 2050s (28). Across Africa,
yields are predicted to change by –17% (wheat),
–5% (maize), –15% (sorghum), and –10% (millet)
and, across South Asia, by –16% (maize) and
–11% (sorghum) under climate change. No mean
change in yield was detected for rice. Knox et al.
(28) concluded that evidence for the impact of
climate change on crop productivity in Africa and
South Asia is robust for wheat, maize, sorghum,
and millet, and inconclusive, absent, or contradictory
for rice, cassava, and sugarcane.
Global-scale climate change impacts at a grid
scale of 200 to 250 km can provide useful information
on shifts in production zones and perhaps
guide the focus of global crop improvement programs
seeking to develop better-adapted crop
varieties. However, much of the adaptation of agricultural
practice to climate change will be driven
by decisions at the farm and farm-enterprise scale.
These decisions need much finer resolution information
than that shown in Fig. 2. At much finer
grid scales of 5 to 20 km there are even greater
limits to the skill of predictive crop science than
at the global scale. Additional uncertainties arise
from how the output of global-scale climate models
is down-scaled, whether input data (such as crop,
soil, topographic, and management information)
are available across the domain for crop simulation
at this scale, as well as questions as to how
skillful the simulation methods are across a finescale
domain. Recent attempts to harmonize modeling
approaches for wheat simulations under
climate change found considerable variation in
projected impacts among models owing to differences
in model structures and parameter values
(29). It is not surprising that the sheer complexity
of food production systems at a very fine scale is
difficult to reproduce in numerical models. However,
there is a real need for studies that test how
well fine-scale simulations compare with observations
in the current climate, as a necessary test of
their utility in future climates.
Although the evidence for direct climate change
effects on crop productivity is reasonable, important
limitations remain for impacts on food availability
more broadly. First, models that adequately
capture expected climate change effects on crops
are only available for the major cereals, groundnut,
and some roots and tubers. Impacts on other important
crops (such as vegetables, pulses, and locally
important, but globally minor, crops) are
often inferred based on similar plant characteristics,
rather than studied explicitly. Second, changes in
grassland productivity and grazing quality and the
quality of crops for livestock feed (30) have hardly
been captured, which limits the understanding of
climate change–livestock linkages. Last, many crop
studies capture the impacts of mean changes in
climate, but are less accurate for changes in weather
extremes, which can have even more important
consequences for crop yields (31).
Food Access
Food access (and utilization) connects to climate
change through indirect, but well-known, pathways.
Access to food is largely a matter of household and
individual-level income and of capabilities and
rights. Food access issues have been studied through
two types of approaches: top-down by models
that attempt to link macro-shocks to household
level responses and adaptation outcomes; and by
community- and household-level studies that try to
assess climate change effects from the bottom up.
The macro-modelsare often composed of
interlinked models—including climate, crop, and
economic models. In this approach, outcomes
from a climate model feed into the crop model
to simulate crop yields under different climate
scenarios. The simulated yields are then used to
make economic forecasts for the impact of climate
change on prices, incomes, trade, and such like.
The macro-models can either be constructed following
a partial equilibrium approach, i.e., studying
the impacts only in one specific sector, such as
agriculture, or as general equilibrium models seeking
to capture the impacts on the whole economy.
The weakness of this approach is that it barely
captures climate adaptations. In contrast, microlevel
studies are often based on detailed household
surveys and usually better account for adaptation
by households and communities to climate change.
An important example is the International
Food Policy Research Institute (IFPRI) International
Model for Policy Analysis of Agricultural
Commodities and Trade (IMPACT) model, which
connects climate change scenarios with food supply
effects and market and price outcomes, and
traces the economic consequences of food availability
drivers to access and utilization of food,
that is, food energy consumption and children’s
nutritional situation (32, 33). Specific findings
are heavily dependent on the assumptions made
about future income and population growth but,
in general, show clear linkages between economic
growth and resilience to climate change (32).
A host of studies is emerging that analyzes
what happens to communities and households
when they are exposed to climate shocks (34–37).
These approaches tend to capture more adaptation
capabilities than macro-models, such as asset
draw-down, job-switching, migration, social policy
responses, and collective action for adaptation
and assistance. But it is difficult to appropriately
capture with micro-level studies the covariate risks
of climate change that cut across broad regions.
Climate change could transform the ability to
produce certain products at regional and international
levels. If it turns out, for example, that the
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geography of biomass production shifts at a global
scale (38), this will have production implications
for all bio-based products—whether food, feed, fuels,
or fiber—and will impinge on food trade flows,
with implications for (farm) incomes and access to
food (39). Similar changes have been observed in
the geography and relative productivity of certain
ocean species, such as shifts between anchovy
and sardine regimes in the Pacific Ocean (40).
Thus, macro-modeling and micro-level analyses
of climate change linkages to food security are
complementary. The prices of the basic resources,
such as land and water, are formed by long-term
expectations (41, 42), and these prices encompass
expectations of climate change, such as revaluation
of land with access to water. Structural consequences
can emerge, particularly when property
rights are lacking and traditional land and water
rights are not protected, as is the case in many
developing countries with food security problems
(43–45); these structural problems lead to erosion
of the assets of the poor, as seen during “land
grabbing” by external and foreign interests (46).
Food Utilization
Food utilization, to attain nutritional well-being,
depends upon water and sanitation and will be
affected by any impact of climate change on the
health environment. Little research has been
done on this dimension of food and nutrition security.
Links with drinking water may be obvious,
when climate variability stresses clean drinking
water availability (47, 48). Hygiene may also be
affected by extreme weather events causing flooding
or drought in environments where sound sanitation
is absent (49–51). In addition, uptake of
micronutrients is adversely affected by the prevalence
of diarrheal diseases, which in turn is
strongly correlated with temperature (52).
Climate change can also impinge on diet quality,
and increased costs may result from measures
required to avoid food contamination stemming
from ecological shifts of pests and diseases of
stored crops or food (53, 54). Science and innovation
have a role to play here, and in recent
years there has been good progress made in improving
food utilization through fortification and
biofortification (55, 56). Vulnerability to food security
shocks needs further research, as do ways to
strengthen adaptive capacities under climate
change, (57) as public policy responses depend
on such insights. For example, appropriate design
of programs transferring income to the poor,
employment-related transfer programs, and early
childhood nutrition actions (58–60) may all need
expanding to respond to climate-related volatilities.
New nutritional stresses are emerging, and
the most striking example has been the recent
“nutrition transition,” i.e., the process by which
globalization, urbanization, and changes in lifestyle
are linked to excess caloric intake, poorquality
diets, and low physical activity. Together,
these factors have led to rapid rises in the incidence
of obesity and chronic diseases, even among
the poor, in developing countries (61). The nutrition
transition will unfold in parallel with climate
change in coming decades, but very little
research on the potentially reinforcing effects of
these phenomena has been done.
Stability of the Food System
The stability of whole food systems may be at
risk under climate change, as climate can be an
important determinant for future price trends
(32), as well as the short-term variability of prices.
Since 2007, the world food equation has been at
a precariously low level and, consequently, even
small shocks on the supply or demand side of
the equation will have large impacts on prices,
as experienced in 2008 (62). Food security of the
poor is strongly affected by staple food prices, as
a large part of an impoverished family’s income
has to be spent on staple foods.
Climate change is likely to increase food
market volatility for both production and supply
[see (63) for the supply side]. Food system stability
can also be endangered by demand shocks,
for instance, when aggressive bioenergy subsidies
and quota policies were applied by the political
economy (64). These sorts of policy shifts, made
in the past decade by the United States and the
European Union, have been motivated in part by
energy security concerns and partly by climate
mitigation objectives (65–67). The resulting destabilization
of food markets, which contributed
to major food security problems, was therefore
partly related to climate change (policy).
The 2008 food crisis stemmed from a combination
of a general reduction of agricultural
productivity and acute policy failures, exacerbated
by export restrictions applied by many
countries, a lack of transparency in markets, and
poor regulation of financial engagement in food
commodity markets (68, 69). A broad set of risks
needs to be considered, of which climate change
is an increasingly important one, that can ripple
out to destabilize food systems, resulting in high
and volatile food prices that temporarily limit
poor people’s food consumption (70–73), financial
and economic shocks that lead to job loss
and credit constraints (74), and risks that political
disruptions and failed political systems cause
food insecurity (75). This complex system of risks
can assume a variety of patterns that could potentially
collide in catastrophic combinations.
What We Need to Know—Research
and Evidence Gaps
Despite a burgeoning literature over the past
5 years or so, much remains unknown about
many food security impacts of climate change.
Getting better evidence will help to some extent.
For example, uncertainties in understanding the
underlying science, social science, and economics
of climate change impacts will reduce as the
evidence base expands with more research. However,
other uncertainties will always remain as they
arise from projections of climate change, sources
of natural variability in climate, and future pathways
of emissions of greenhouse gases.
Four broad priorities for future research emerge
from our review: (i) gathering evidence on the
effects of climate change impacts on the food access,
utilization, and stability dimensions in order
to achieve a more holistic understanding of food
security; (ii) understanding the indirect impacts
of climate change on food security requires more
comprehensive analytical approaches and sophisticated
modeling, including links to the political
economy; (iii) improving projections of regional
climate change effects on food security at country
level and on smaller scales that are crucial for
decision-making for adaptation of food systems;
(iv) better integrating of human dimensions of climate
change impacts into food security planning—
because food systems are ultimately driven by
people and their behavioural responses to real and
perceived changes in their local climate—that will
be central to the adaptation to climate change and
actions to address hunger.
What We Know We Know—Messages
for Decision-Makers
Decisions still need to be taken by policy-makers
and practitioners confronted with the prospect of
climate change impacts on food security, despite
very real uncertainties in current knowledge and
future trends. For those making decisions, we propose,
with a fair degree of confidence from the
existing evidence, six precepts for the impacts of
climate change on food security:
1) Climate change impacts on food security
will be worst in countries already suffering high
levels of hunger and will worsen over time.
2) The consequences for global undernutrition
and malnutrition of doing nothing in response
to climate change are potentially large and will
increase over time.
3) Food inequalities will increase, from local
to global levels, because the degree of climate
change and the extent of its effects on people will
differ from one part of the world to another, from
one community to the next, and between rural
and urban areas.
4) People and communities who are vulnerable
to the effects of extreme weather now will
become more vulnerable in the future and less
resilient to climate shocks.
5) There is a commitment to climate change
of 20 to 30 years into the future as a result of
past emissions of greenhouse gases that necessitates
immediate adaptation actions to address
global food insecurity over the next two to three
decades.
6 ) Extreme weather events are likely to become
more frequent in the future and will increase risks
and uncertainties within the global food system.
All of these precepts support the need for
considerable investment in adaptation and mit512
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igation actions to prevent the impacts of climate
change from slowing progress in eradicating
global hunger and undernutrition. A wide range
of potential adaptation and resilience options
exist and more are being developed. These need
to address food security in its broadest sense and
to be integrated into the development of agriculture
worldwide. Building agricultural resilience,
or “climate-smart agriculture,” through improvements
in technology and management systems
is a key part of this, but will not be sufficient on
its own to achieve global food security. The whole
food system needs to adjust to climate change,
with strong attention also to trade, stocks, and to
nutrition and social policy options. We need to
work toward what could be termed a climatesmart
food system that addresses climate change
impacts on all dimensions of food security.
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Acknowledgments: We thank H. Li, Q. Zhang, and F. Zhang
of CABI for conducting the bibliographic analysis. T.W. was
partly supported by the UK-China Sustainable Agriculture
Innovation Network programme of the UK Department for
Environment, Food and Rural Affairs, International Sustainable
Development Fund (DC09-07).
10.1126/science.1239402
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Climate Change Impacts on Global Food Security
Tim Wheeler and Joachim von Braun
DOI: 10.1126/science.1239402
Science 341 (6145), 508-513.
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