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Chapter 1.1
Climate Change, Population Growth, and Crop
Production: An Overview
Hermann Lotze-Campen
Introduction
The publication of the Stern Review on the
Economics of Climate Change in 2006 and the
Fourth Assessment Report by the Intergovernmental
Panel on Climate Change (IPCC) in 2007
have pushed the scientific and public debate on
climate change a decisive step forward. It is now
beyond doubt that anthropogenic greenhouse gas
(GHG) emissions are the main cause for recently
observed climate change and that early
and bold mitigation measures will eventually be
much cheaper than later adaptation to potentially
drastic climate impacts. The agricultural sector is
directly affected by changes in temperature, precipitation,
and CO2 concentrations in the atmosphere,
but it is also contributing about one-third
to total GHG emissions, mainly through livestock
and rice production, nitrogen fertilization,
and tropical deforestation. Agriculture currently
accounts for 5% of world economic output, employs
22% of the global workforce, and occupies
40% of the total land area. In the developing
countries, about 70% of the population lives in
rural areas, where agriculture is the largest supporter
of livelihoods. In many developing countries,
the economy is heavily depending on agriculture.
The sector accounts for 40% of gross
domestic product (GDP) in Africa and 28% in
South Asia. However, in the future, agriculture
will have to compete for scarce land and water resources
with growing urban areas and industrial
production.
A large share of the world’s poor population
lives in arid or semiarid regions, which are already
characterized by highly volatile climate
conditions. Under conditions of future climate
change, a worldwide increase in climate variability
and extreme weather events is very likely.
The connections between agricultural development
and climate change reveal some fundamental
issues of global justice. The industrialized
countries, mostly located in medium to high latitudes,
are responsible for the major share of
accumulated GHG emissions. They are economically
less dependent on agriculture, they will be
less affected by climate impacts, and they have
on average a higher adaptive capacity. Most developing
countries are located in the lower latitudes,
they are dependent on agriculture, they
will be strongly affected by climate impacts, and
they have lower (or nonexistent) adaptive capacity.
Creating more options for climate change
adaptation and improving the adaptive capacity
in the agricultural sector will be crucial for improving
food security and preventing an increase
Crop Adaptation to Climate Change, First Edition. Edited by Shyam S. Yadav, Robert J. Redden, Jerry L. Hatfield,
Hermann Lotze-Campen and Anthony E. Hall.
c 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd.
1
COPYRIGHTED
MATERIAL
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2 CROP ADAPTATION TO CLIMATE CHANGE
in global inequality in living standards in the future.
However, in the developing world, this is
often prevented by the lack of information, financial
resources, and good governance.
Global scenarios on future
greenhouse gas emissions and
population growth
Future emissions of anthropogenic GHG mainly
depend on population growth, socioeconomic
development, and technological change. Future
trends in these driving forces are highly uncertain,
especially over the course of the next
decades until the end of the century. For a systematic
description of the range of possible futures,
the IPCC has developed a set of long-term
emission scenarios that were published in the
Special Report on Emission Scenarios (SRES;
Nakicenovic et al. 2000). Four different narrative
storylines were developed to represent different
demographic, social, economic, technological,
and environmental conditions and trends, thus
covering a wide range of possible GHG emission
outcomes. For each storyline, several emission
scenarios were developed using different
integrated assessment modeling approaches.
Table 1.1.1 summarizes the main driving
forces for the four emission scenarios by the end
of the century.
The A1 storyline describes a future world of
very rapid economic growth, global population
that peaks at about 9 billion in mid-century and
declines thereafter, and the rapid introduction of
new and more efficient technologies. The underlying
theme is that regions will converge and
cultural and social interactions will increase with
a substantial reduction in regional differences in
per capita income. The scenario groups are determined
by different directions of technological
change in the energy system. A1FI is fossil intensive,
A1T heavily uses nonfossil energy sources,
and the A1B is a scenario with a balance across
all energy sources.
The A2 storyline describes a very heterogeneous
world. The underlying theme is selfreliance
and preservation of local identities. Population
will continuously increase, up to 15 billion
in 2100, and economic development is primarily
regionally oriented. Per capita economic
growth and technological change are more fragmented
and slower than in other storylines. The
B1 storyline describes a convergent world with
the same global population as in A1 that peaks
at mid-century and declines thereafter. However,
major differences come from rapid changes in
economic structures toward a service and information
economy, with reductions in material
intensity and the introduction of clean and
resource-efficient technologies. The main feature
is a global solution to economic, social, and
environmental sustainability with improved equity
but without additional climate initiatives.
The B2 storyline describes a world of local solutions
to economic, social, and environmental
sustainability. It is a world with continuously increasing
global population at a rate lower than
A2 (about 10 billion in 2100), intermediate levels
of economic development, and less rapid and
more diverse technological change than in the
B1 and A1 storylines.
Figure 1.1.1 shows the projected temperature
increases for the four SRES scenario groups,
including the different energy technology options
of A1. Each emission scenario was analyzed
with several global climate models, to take
uncertainties about the climate sensitivity of different
models into account. Highest temperature
increases are projected for A1FI due to very high
emissions. The mean model results for global
temperature increase across all climate models
range between 2.4◦
C (B1) and 4.6◦
C (A1FI),
compared to the preindustrial level. Several models
show a wider range of outcomes, possibly as
low as 1.6◦
C for the B1 scenario but also as
high as 6.4◦
C for the fossil-fuel-intensive A1FI
scenario.
Climate impacts on crop
productivity
Plant growth and yield will be both positively and
negatively affected by climate change. Diverging
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CLIMATE CHANGE, POPULATION GROWTH, AND CROP PRODUCTION 3
Table 1.1.1. Overview of main driving forces for the four SRES storylines in 2100.
Peoplea
billion (B)
Economic
growthb % p.a.
Incomec
GDP/capita
Primary energy
use
Hydrocarbon
resource used
Land use
changeb
A1 Low
∼7 B.
1.4 IND
5.6 DEV
Very high
1990-20: 3.3
1990-50: 3.6
1990-100: 2.9
Very high
IND 107,300
DEV 66,500
Very high
2.226 EJ
Low intensity
4.2 MJ/US$
Scenario:
Oil low—VH
20.8 ZJ
Gas high—VH
42.2 ZJ
Coal med—VH
15.9 ZJ
Low
1990-100:
cropland +3%
grassland +6%
forests +2%
A2 High
15 B.
2.2 IND
12.9 DEV
Medium
1990-20: 2.2
1990-50: 2.3
1990-100: 2.3
Low in DEV
Medium in
IND
IND 46,200
DEV 11,000
High
1,717 EJ
High intensity
7.1 MJ/US$
Scenario:
Oil VL—med
17.3 ZJ
Gas low—high
24.6 ZJ
Coal Med - VH
46.8 ZJ
Medium
n.a.
B1 Low
∼7 B.
1.4 IND
5.7 DEV
High
1990-20: 3.1
1990-50: 3.1
1990-100: 2.5
High
IND 72,800
DEV 40,200
Low
514 EJ
Very low
intensity 1.6
EJ/US$
Scenario:
Oil VL—high
19.6 ZJ
Gas med—high
14.7 ZJ
Coal Vl—high
13.2 ZJ
High
1990-100:
cropland −28%
grassland −45%
forests +30%
B2 Median
∼10 B.
1.3 IND
9.1 DEV
Medium
1990-20: 3.0
1990-2050: 2.8
1990-100: 2.2
Medium
IND 54,400
DEV 18,000
Medium
1,357 EJ
Medium
intensity 5.8
MJ/US$
Scenario:
Oil low—med
19.5 ZJ
Gas low—med
26.9 ZJ
Coal low—VH
12.6 ZJ
Medium
1990-100:
cropland +22%
grassland +9%
forests +5%
Source: Nakicenovic et al. (2000), Table 4.4a, http://www.grida.no/climate/ipcc/emission/097.htm.
aIND, industrialized countries; DEV, developing countries.
b1990 > 2000.
cUS$.
dVL, very low; med, medium; VH, very high.
effects are caused by rising CO2 concentrations,
higher temperatures, changing precipitation patterns,
changing water availability, increased frequency
of weather extremes (i.e., floods, heavy
storms and droughts), climate-induced soil erosion,
and sea-level rise. While some of these
impacts have been studied in isolation, complex
interactions between different factors and
especially extreme events are still not well
understood.
CO2 fertilization
Yields of most agricultural crops increase under
elevated CO2 concentration. Free air carbon
enrichment (FACE) experiments indicate productivity
increases in the range of 15–25% for
C3 crops (like wheat, rice, and soybeans) and
5–10% for C4 crops (like maize, sorghum, and
sugarcane). Higher levels of CO2 also improve
water-use efficiency of both C3 and C4 plants.
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4 CROP ADAPTATION TO CLIMATE CHANGE
Fig. 1.1.1. Projected temperature increases for the four SRES emission scenario groups.
(Source: IPCC 2007, p. 14.)
However, the experiments do not address important
colimitations because of water and nutrient
availability. Some studies expect much
less favorable crop response to elevated CO2
in practice than that asserted on experimental
sites (e.g., Long et al. 2006), while others agree
with findings from FACE experiments (Tubiello
et al. 2007). Thus, the magnitude of the positive
yield effect due to enhanced CO2 concentration
is still uncertain (Parry et al. 2004; Easterling
et al. 2007).
Higher temperatures
Warming is observed over the entire globe, but
with significant regional and seasonal variations.
Highest rates can be found at Northern latitudes
and during winter and spring (Solomon et al.
2007). In the Northern Hemisphere, in higher
latitudes, rising temperatures imply lengthening
of the growing season by 1.2–3.6 days per decade
(Gitay et al. 2001). This allows earlier planting
of crops in spring, earlier maturing and harvest,
and the possibility for two or more cropping cycles.
An expansion of suitable crop area may become
possible in the Russian Federation, North
America, Northern Europe, and Northeast Asia.
In contrast, significant losses are predicted for
Africa due to heat and water stress and an expansion
of arid and semiarid regions (Fischer
et al. 2005). Temperature increases are likely to
support positive effects of enhanced CO2 until
temperature thresholds are reached. Beyond
these thresholds, crop yields will be negatively
affected. Increased water supply can help to balance
high temperatures. In the tropics, additional
warming of less than 2◦
C will lead to crop yield
losses, while crops in temperate regions will
broadly benefit from temperature increases of
up to 2◦
C. Further warming will negatively affect
plant health in temperate regions (Easterling
et al. 2007).
Water availability
Agriculture highly depends on water availability.
More than 80% of global cropland is rainfed,
but irrigated cropland with an area share of
16% produces about 40% of the world’s food.
Agricultural irrigation accounts for around 70%
of global freshwater withdrawals (Gitay et al.
2001). Because of growing global food demand
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CLIMATE CHANGE, POPULATION GROWTH, AND CROP PRODUCTION 5
and rising temperatures, even more water will
be required in the future. Climate impacts on
crop productivity will fundamentally depend on
precipitation changes. Precipitation projections
show large variability of quantity and distribution.
This is also due to the fact that historical climate
records as an input for modeling are scarce
in many poor countries. Annual mean runoff
largely follows projected changes in precipitation
with an increase in high latitudes and the
wet tropics, and with a decrease in mid-latitudes
and some parts of the dry tropics (Solomon et al.
2007). The decline in water availability will affect
areas currently suitable for rainfed crops,
like the Mediterranean basin, Central America,
and subtropical regions of Africa and Australia
(Easterling et al. 2007). Moreover, in warmer and
dryer regions, agricultural water demand will increase.
Global irrigation requirements are estimated
to increase by 5–8% by 2070 with regional
differences of up to +15% in South Asia
(D¨oll 2002). While irrigated agriculture is expected
to become more important, water supply
may be insufficient. In regions that are depending
on steady water supplies from glaciers
(e.g., Andes and Himalaya), water availability
may increase in the near to medium term due
to accelerating glacier retreat, whereas it may
break down later, once glaciers are completely
melted. In some regions (e.g., northern India and
Midwest United States) groundwater is depleted
at fast rates, which could clearly lead to water
shortages in the future. In addition to decreasing
water supply, agriculture in many fast-growing
regions will also face increasing competition for
water due to rising demand from households and
industry.
Climate variability, extreme events,
and sea-level rise
Extreme climate events such as heat waves,
heavy storms, floods, or droughts may damage
crops in specific development stages. A substantial
and widespread increase in the number of
heavy rainfall events is expected, even in regions
where total precipitation amount decreases
(Solomon et al. 2007). Heavy rainfalls are very
likely in Southern and Eastern Asia and in Northern
Europe, which are major agricultural production
areas. On the other hand, observations show
an increase in frequency and duration of warm
weather extremes. In many regions, especially
in the tropics and subtropics, droughts have been
longer and more intensive since the 1970s because
of higher temperatures and reduced precipitation
(Solomon et al. 2007). Climate change
will deepen these trends. In arid and semiarid regions,
higher rainfall intensity will increase risks
of soil erosion and salinization. Rice yield is already
close to the limit of maximum temperature
tolerance in South Asia. Thus, even higher
temperatures will negatively affect yields. Additionally,
increasing flood frequency will damage
crop production in countries like Bangladesh.
In the United States, heavy precipitation events
are expected to cause severe production losses
already by 2030 (Rosenzweig and Hillel 1995;
Easterling et al. 2007). The European heat wave
in the summer of 2003 with temperatures of 6◦
C
above long-term averages and severe precipitation
shortfalls caused severe economic losses for
the agricultural sector across Europe. In Northern
Italy, a record yield drop of 36% was observed,
while in France maize yield was reduced
by 30% when compared to 2002 (Easterling
et al. 2007).
In low-lying countries with long coastlines,
sea-level rise will threaten large areas of fertile
land. This is a special problem, e.g., in
Bangladesh and many Pacific Islands. Another
problem related to rising sea levels is saltwater
intrusion, which may negatively affect soil fertility
and quality of irrigation water in coastal
areas.
Soil degradation
Climate change affects soils by increasing the
rate of nutrient leaching and soil erosion. Nutrient
conservation is affected by warmer temperatures
because higher temperatures are likely
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6 CROP ADAPTATION TO CLIMATE CHANGE
to increase the natural decomposition of organic
matter because of a stimulation of microbial activity.
If mineralization exceeds plant uptake, nutrient
leaching will be the consequence. It primarily
occurs when plant demand is low and
rising soil temperature increases nitrogen mineralization
rates. This process is enforced by increased
precipitation and loss of snow cover as
predicted for many temperate regions (Niklaus
2007). Soil erosion is increased by intensive rainfall,
which is likely to increase under climate
change. One percent increase in precipitation is
expected to lead to 1.5–2% increase in erosion
rates (Nearing et al. 2004). Extreme rainfall and
shifting from snow to rain will also increase the
rate of erosion. Changes of plant biomass can
further increase these effects: plant canopies reduce
soil erosion by weakening the power of
rain, roots stabilize soils, and crop residues reduce
sediment transportation. In arid and semiarid
regions, dry soils are sensitive to soil erosion
through wind and rain. Increased frequency
of droughts further intensifies erosive losses as
plant biomass and its positive effects on soils are
reduced (Nearing et al. 2004; Niklaus 2007).
Weeds, pests, and pathogens
In current agriculture, preharvest losses to
pests in major food and cash crops are estimated
to be 42% of global potential production
(Gitay et al. 2001). Temperature rise and elevated
CO2 concentration could increase plant
damage from pests in future decades, although
only a few quantitative analyses exist to date
(Easterling et al. 2007; Ziska and Runion 2007).
Weeds, like crops, show positive response to
elevated CO2. Moreover, weeds show a larger
range of responses, including larger growth, to
elevated CO2 because of their greater genetic
diversity (Ziska and Runion 2007). Several important
crop weeds in the United States have
expanded since the 1970s, which is consistent
with climate trends (Gitay et al. 2001). However,
future weed distribution and the accompanied
changes in weed–crop competition remain
highly uncertain. Temperature rise will boost insect
growth and development by increasing geographical
distribution and increasing overwintering
(Ziska and Runion 2007). Pathogens are
recognized as a significant limitation on agronomic
productivity. While elevated CO2 will not
directly affect the pathogens, it will alter plant
defense mechanisms. Especially, higher winter
temperatures will lead to an increasing occurrence
of plant diseases in cooler regions (Ziska
and Runion 2007).
Climate impacts on agricultural markets
According to currently available studies, aggregated
global impacts of climate change on world
food production are likely to be small. Parry
et al. (2004) predict negative impacts on world
crop production by −5% by the end of the century.
According to Fischer et al. (2005), production
losses in developing countries in the range
of 5–15% will be compensated by similar increases
of production in the developed countries,
in particular North America and Russia.
Thus, climate change will result in larger trade
flows from mid- and high-latitudes to the low
latitudes (Easterling et al. 2007). However, most
of the studies available to date only cover gradual
scenarios of climate change and related impacts.
If tipping points in the climate system
are transgressed, the picture is likely to become
much bleaker (Battisti and Naylor 2009). Even
without climate change, there will be a growing
dependency of developing countries on net
cereal imports. Climate change will further increase
this dependency by 10–40% (Fischer et al.
2005). In the past, the average rate of productivity
growth in agriculture and food production
exceeded population growth. Supply exceeded
demand, which resulted in a long-term decline
of real food prices until the turn of the millennium.
Even if the strong food price increases
in 2007/2008 may have been an exception, it
can be expected that world food prices will
gradually increase in the future. Besides climate
change, the dynamics of population, income, and
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CLIMATE CHANGE, POPULATION GROWTH, AND CROP PRODUCTION 7
technology will continue to play an important
role. Furthermore, depending on technological
and policy changes in the energy sector, an increasing
demand for bioenergy will have an impact
on agricultural markets. In poor, net food
importing countries, food security could deteriorate
as a result. For countries with a strong production
potential, bioenergy demand could also
become an engine for agricultural and economic
growth.
Climate impacts on food security
Food security has four major components: Food
availability through production and trade; stability
of food supplies; access to food; and
actual food utilization. They all can be affected
by climate change (Gregory et al. 2005;
Easterling et al. 2007). Assessments of crop production
can therefore only provide a partial assessment
of climate change impacts on food security.
In addition, climate change is not the only
factor that may cause food security problems.
Regional conflicts, changes in international trade
agreements and policies, infectious diseases, and
other societal factors may exacerbate the impacts
(Easterling et al. 2007). The capacity to cope
with environmental stress is as important as the
degree of exposure to climate-related stresses.
Thus, projections of undernourishment depend
on climate impacts and also on economic development,
technical conditions, and population
growth (Gregory et al. 2005). At the beginning
of the millennium, between 800 and 900 million
people were at risk of hunger. Most of them
lived in Asia and sub-Saharan Africa (FAO 2006,
p. 8). In the future, many factors including climate
change and socioeconomic development
will influence the number of people at risk, and
there are still a lot of uncertainties about regional
climate impacts on food supply and demand.
However, it is very likely that sub-Saharan
Africa will surpass South Asia as the most
food-insecure world region (Tubiello and Fischer
2007). Few studies have tried to quantify the
impacts of climate change and socioeconomic
factors on food security (Fischer et al. 2002,
2005; Parry et al. 2004; Tubiello and Fischer
2007). They indicate that the number of people
at risk of hunger will mostly depend on socioeconomic
development. Economic growth and slowing
population growth can significantly reduce
the number of people at risk of hunger. In a pessimistic
scenario with strong global warming,
high population growth, and no CO2-fertilization
effects, the number of additional people at risk
of hunger may be as high as 500–600 million
by 2080 (Parry et al. 2004). Again, the situation
may become even worse, if tipping points in
the climate system are transgressed (Battisti and
Naylor 2009).
Adaptation options in agriculture
Agricultural vulnerability
In the past, adaptation in agriculture was the
norm rather than the exception. Farmers have
demonstrated sufficient adaptive capacity to cope
with weather variations on weekly, seasonal, annual
and even longer timescales (Burton and Lim
2005; Rosenzweig and Tubiello 2007). Modern
agricultural technologies have minimized climate
impacts through irrigation, the use of pesticides
and fertilizers, and the manipulation of
genetic resources (Kandlikar and Risbey 2000).
In the future, however, climate will change at
a rate that has not been previously experienced
in human history. Adaptive capacity of farmers
is determined by their wealth, human capital,
information and technology, material resources
and infrastructure, and institutions and entitlements
of the society (Kandlikar and Risbey 2000;
Belliveau et al. 2006; Easterling et al. 2007). It is
obvious that rich countries are better equipped
to cope with climate variations than developing
countries, where decisions are made in the
context of the local agricultural cycle, poverty,
and often limited access to markets. Many possible
adjustments are prevented by the lack
of information, financial resources, and institutional
support. New technologies are often not
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8 CROP ADAPTATION TO CLIMATE CHANGE
implemented due to lack of education (Kandlikar
and Risbey 2000; Smithers and Blay-Palmer
2001).
Adjustments in production technology
Technical improvements and management adjustments
at the farm level include the following:
r Shifted dates of planting allow farmers to take
advantage of the longer growing season that
is permitted by higher winter temperatures in
higher latitudes. Earlier planting can lead to
an increase in the yield potential by using cultivars
that need longer time to mature. The
potential for earlier harvesting can avoid heat
and drought stress in late summer (Easterling
1996; Olesen and Bindi 2002; Rosenzweig and
Tubiello 2007).
r New crop varieties can provide more appropriate
thermal requirements and increased resistance
to heat shock and drought. Breeding
of new varieties is certainly a major option for
improved adaptation, but development of new
varieties, which are well adapted to specific
regional conditions, is expensive and typically
needs a decade or longer until they can be
distributed to farmers. Hence, breeding programs
need to be planned at a longer timescale
(Olesen and Bindi 2002; Smit and Skinner
2002; Rosenzweig and Tubiello 2007).
r Altering and widening existing crop rotations
can help to adapt to changing climate conditions
by introducing new, better adapted crop
types. A broader crop mix will decrease the
dependency on weather conditions in a certain
growing season and hence stabilize production
and farm income under higher climate
variability. However, it will also require technical
and management adjustments and may
reduce some gains from specialization in the
production of certain crops (Olesen and Bindi
2002; Easterling et al. 2007; Rosenzweig and
Tubiello 2007).
r Rising water demand caused by higher temperatures
can be balanced by improved water
management and irrigation. A shift from
rainfed to irrigated agriculture may be an option,
although water availability, costs, and
competition with other economic sectors need
to be considered. Adjustments like timing of
irrigation and improvement of water-use efficiency
can ensure water supply for crops
even under warmer and dryer climate. Moreover,
crop residue retention and altered tillage
practices can reduce water demand. Various
types of low-cost “rainwater harvesting” practices
have been developed in poor countries
(Easterling 1996; Smithers and Blay-Palmer
2001; Smit and Skinner 2002).
These adjustments, alone or in combination,
can minimize climate impacts on agriculture. On
average, adaptation can provide around 10–15%
yield benefit compared to a situation without
adaptation measures. Thus, adaptation may shift
negative yield changes caused by rising temperatures
from 1.5◦
C to 3◦
C warming in low latitude
regions and from 4.5◦
C to 5◦
C in mid- to
high-latitude regions. If temperatures rise above
these thresholds, the adaptive capacity is likely
to be exhausted and severe losses are to be expected
(Easterling et al. 2007). However, interactions
between different adaptation options and
economic, institutional, and cultural barriers to
adaptation are not considered in most available
studies (Easterling et al. 2007).
Insurance schemes
In addition to changes in production technology,
insurance schemes (e.g., crop insurance
or income stabilization programs) can provide
compensation for crop and property damages
caused by climate-related hazards, like droughts
or floods. However, these options are not available
for farmers everywhere, not even in all developed
countries (Bielza et al. 2007). There
are specific challenges for insurance schemes in
the agricultural sector. Extreme weather events
can affect a large group of people at the same
time, and the insurance pool may not be able to
cover all the claims. If reinsurance mechanisms
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CLIMATE CHANGE, POPULATION GROWTH, AND CROP PRODUCTION 9
or government support schemes are not available,
insurance companies would have to charge high
premiums, which may be unaffordable for most
farmers. Thus, agricultural insurance schemes
are usually supported by the public sector to provide
broad coverage at affordable premiums (European
Commission 2001; Bielza et al. 2007). In
some developed countries, financial support for
crop insurance and disaster payments are a major
part of their agricultural sector policies. The
United States, Canada, and Spain have the most
developed agricultural insurance policies. Up to
60% of farmers in these countries purchase at
least one insurance policy (Garrido and Zilberman
2007). Insurance in developing countries is
only available to a limited extent. In India, the
National Agriculture Insurance Scheme was implemented
to protect farmers against losses due
to crop failure caused by drought, flood, hailstorm,
cyclone, fire, pests, and diseases. All food
crops, oilseeds, and annual commercial and horticultural
crops are covered. However, only 4%
of farmers are currently protected by the crop
insurance scheme. Almost half of the farmers in
India still do not even know about the insurance
option (Bhise et al. 2007).
International trade
On average, global food production is likely to
be sufficient to meet global consumption over
the coming decades. However, climate change
will reduce crop yield in some regions, while
it will have beneficial effects in others. A wellfunctioning
system of international trade flows,
which is responsive to price signals, will be
needed to balance production and consumption
between and within nations. Increased agricultural
output in a region where agricultural production
improves can then be used to compensate
potential losses in other regions (Juli´a and
Duchin 2007). It has been shown in the past that
open markets are promoting economic development.
In the agricultural sector, protectionist
policies in the industrialized countries are still
preventing the developing countries from participating
to a larger share in international markets.
In the future, international trade between rich
and poor countries, but also among poor countries,
can to a certain degree serve as an insurance
mechanism against severe production shortfalls
due to extreme weather events. Even in a changing
climate, it is unlikely that extremely bad harvests
will occur at the same time in several major
supply regions.
Government policies to support
adaptation in agriculture
The adaptive capacity at the farm level is unlikely
to be sufficient in many poor regions. Nonclimatic
forces such as economic conditions and
policies have significant influences on agricultural
decision-making. Therefore, changes in national
and international policies for the agricultural
sector are needed to support adaptation at
the local level (Smit and Skinner 2002; Rosenzweig
and Tubiello 2007). The weight given to
climate change in the policy process will depend
on national and local circumstances, including
local risks, needs, and capacities. Further reform
of agricultural policies in developed countries
should not only make agricultural production
more climate-friendly, but also provide better
options for poor countries to improve their adaptive
capacity. More financial resources have to be
shifted away from direct farm income support toward
better agricultural education, research, and
technological development to assure yield improvement
and yield stabilization under changing
climate and market conditions. Improved
infrastructure is needed for the extension of irrigation
or for appropriate storage, transportation
facilities, and better weather forecasting and climate
impact research. Low density of weather
stations and limited historical weather data, especially
in Africa and other developing regions,
is one reason for high uncertainties in current climate
model scenario outputs. This in turn makes
it more difficult for these countries to develop
appropriate adaptation strategies (Belliveau et al.
2006; Easterling et al. 2007).
Improved policies can also guide transitions
where major land use changes, changes of
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10 CROP ADAPTATION TO CLIMATE CHANGE
industry locations, or migration occur. Financial
and material support can create alternative livelihood
options. Planning and management of such
transitions may also result in less habitat loss and
lower environmental damage. The establishment
of functioning and accessible markets for inputs
such as seeds, fertilizers, and labor, as well as
financial services can improve income security
for farmers (Easterling et al. 2007).
Conclusions
Climate impacts on agriculture strongly depend
on regional and local circumstances. Adaptive
capacity and adaptation options are largely determined
by the level of economic development
and institutional setting, which also differ widely
across the globe. While positive and negative
effects of climate change on global agriculture
may on average almost compensate each other,
the uneven spatial distribution is likely to affect
food security in a harmful way in many
regions. Food security could be severely threatened,
if tipping points in the climate system are
transgressed. One prominent example of a climate
tipping point is the dynamics of the Indian
monsoon, which could be disrupted under
certain conditions (Zickfeld et al. 2005). This
would negatively affect agricultural production
conditions in large parts of South Asia. Generally
speaking, developing countries in the tropics
will face the strongest direct climate impacts,
while having the lowest level of adaptive capacity.
The most affected regions are expected
to be sub-Saharan Africa and the Indian subcontinent.
If global mean temperature will rise
by more than 2–3◦
C compared to preindustrial
levels, countries in mid and high latitudes will
also be strongly affected. Uncertainties still prevail
with regard to future precipitation patterns
and water availability at the regional level, the
impacts of extreme events on agriculture, and
changes in soil fertility and agricultural pests and
pathogens. Further research is also required on
the interactions between various climate-related
stress factors. The role of CO2 fertilization in
connection with nutrient and water limitations
needs further clarification. Negative climate impacts
on agriculture may be reduced through
a range of adaptation measures. Adjustments
in production technology and soil management,
crop insurance schemes, diversified international
trade flows, and better designed agricultural policies
can improve regional food availability and
security of farm income. However, limited resources
such as fertile soils, freshwater, financial
means, and institutional support may often prevent
the required adjustments.
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