Climate Change and Global Food Security - Section 3 ppt

devel-Table 10.1 Effects of Climate Change on Global Food Production Under Various Scenarios Percent Change in Yield HadCM3 2080s HadCM2 2080s... 10.4.4 Long-Term Effects on Agriculture

Section III

Climate Change and Agronomic Production

10

Climate Change, Agriculture, and

Sustainability CYNTHIA ROSENZWEIG AND DANIEL HILLEL

CONTENTS

10.1 Climate Change 245

10.2 Goals of Impact Studies 247

10.3 Agro-Ecosystem Processes 247

10.4 What We Have Learned 249

10.4.1 Agriculture Regions Will Experience Change over Time 249

10.4.2 Effects on Agricultural Production Systems Will Be Heterogeneous 251

10.4.3 Agricultural Production in Many Developing Countries Is Especially Vulnerable 251

10.4.4 Long-Term Effects on Agriculture Are Negative 253

10.4.5 Agricultural Systems Can Adapt, but Not Completely 253

10.5 Key Interactions 254

10.5.1 El Niño-Southern Oscillation 254

10.5.2 Water Resources 256

10.5.3 Agricultural Pests 256

10.6 Mitigation and Adaptation Responses 258

10.6.1 Mitigation 259

10.6.2 Adaptation 260

10.7 Interactions 262

10.7.1 Research Pathways 263

10.7.1.1 Climate Variability and Change 263

10.7.1.2 Observed Effects of Warming Trends 264

10.7.1.3 Global and Local Scales 265

10.8 Conclusion 266

References 266

The first global climate model experiments projecting the atmo-spheric responses of increasing carbon dioxide (CO2) and other greenhouse gases were published in the early 1980s Soon after, research began on the agricultural implications of the changing atmospheric composition and its projected climate shifts As the primary land-based human activity most intimately con-nected with climate and as the very foundation for human nutrition and indeed survival, agriculture naturally became a key focus for early climate change impact studies

Through the ensuing two decades, scientists have employed a variety of analytic approaches in a multitude of studies to answer such research questions as: What might be the major effects of climate changes in the 21st century? Are some regions likely to gain, while others lose? What response measures are indicated? How climate change affects agricul-ture and how agriculagricul-ture responds to a changing climate will invariably shape the sustainability of this vital sector

Research in the area of climate change impacts on agricul-ture has involved field experiments, regression analyses, and modeling studies The fields concerned have included agronomy, resource economics, and geography Climate change and

agriculture studies continue, with broad-brush explorations ing way to more detailed studies of biophysical processes andsocial responses In this chapter, we review some of the mainlessons learned from two decades of research on climate changeand agriculture, and then delineate several pathways for con-tinuing research that will help to elucidate further the interac-tions of climate change and agricultural sustainability.

giv-10.1 CLIMATE CHANGE

Climate change projections are fraught with much tainty in regard to both the rate and magnitude of tempera-ture and precipitation alterations in the coming decades Thisuncertainty derives from a lack of precise knowledge of howclimate system processes will change and of how populationgrowth, economic and technological development, and landuse will proceed in the coming century (IntergovernmentalPanel on Climate Change [IPCC], 2000, 2001)

uncer-Nevertheless, three points regarding climate change can

gas concentrations have increased progressively since thebeginning of the Industrial Revolution Second, the naturalpresence of greenhouse gases is known to affect the planetaryenergy balance, causing the planet to be warmer than it would

be otherwise Thus, any increases in greenhouse gases willtend to enhance the natural “greenhouse effect.” Third, theplanet has indeed been warming over the last century, espe-cially in the most recent two and a half decades

The IPCC has attributed the observed warming over thelast century to anthropogenic emissions of greenhouse gases,especially carbon dioxide (CO2), methane (CH4), and nitrousoxide (N2O) (IPCC, 2001) Thus, anthropogenic emissions ofgreenhouse gases appear to be altering our planetary energybalance and to be manifested in a large-scale warming of theplanet If warming continues at the global scale, the associa-tion among greenhouse gas emissions, greenhouse effect, andsurface warming will trend toward greater and greater cer-tainty The ultimate significance of the climate change issue

is related to its planetary scale

be made with some certainty (Figure 10.1) First, greenhouse

Some of the infrared radiation passes through the atmosphere, and some

is absorbed ane re-emitted

in all directions by greenhouse gas molecules The effect of this is to warm the Earth's surface and the lower atmosphere.

Some solar radiation

is reflected by the Earth and the atmosphere.

absorbed by the Earth's

surface and warms it. Infrared radiation isemitted from the

5 year average

10.2 GOALS OF IMPACT STUDIES

Many of the climate change studies done to date, particularlythe early ones, were undertaken to aid national policymakers

to assess the significance of global climate change and itsimplications for broad regions as well as for whole countries.These studies are thus “policy relevant” in the sense that theymay contribute to national decisions on whether and how toparticipate in the U.N Framework Convention on ClimateChange (UNFCCC) and the Kyoto Protocol Questions hererevolve around how serious the ultimate warming may be;who may be the “winners and losers”; and what the potential

is for adaptation in broad-brush terms

Recently, attention has been turning to how to respond

to global climate change, including more detailed explorations

of adaptation strategies and adaptive capacities at finer tial scales — even down to individual villages Many of theseadaptation studies are focused on defining vulnerability andrepresent a link between the experience of current climateextremes, disaster management, and potential decadal-to-century warming A further shift in focus involves the poten-tial role of carbon sequestration in climate change mitigation,and to what extent this can reduce the anthropogenic build-

spa-up of greenhouse gases in the atmosphere

10.3 AGRO-ECOSYSTEM PROCESSES

Determining what the net effect of a changing climate may

be on an agro-ecosystem is complicated due to the interactions

of several simultaneous biophysical processes In some cases,changes in climate may be beneficial, while in others they

Figure 10.1 (opposite page) The three certainties of global mate change: (A) the greenhouse effect and planetary energy bal-ance; (B) atmospheric concentrations of greenhouse gases, 1860 topresent; and (C) mean global surface temperature, 1860 to present

cli-(From OSTP 1997 Climate Change: State of Knowledge Office of

Science and Technology Policy, Washington, DC.)

may be detrimental (Figure 10.2) On the beneficial side,

increasing levels of atmospheric CO2 have been shown toincrease photosynthesis rates and to increase stomatal resis-tance in crops, leading to overall increased water-useefficiency (Kimball et al., 2002) These processes have beencalled “CO2fertilization.”

Another beneficial impact would be the prolongation ofcrop growing seasons in areas where they are now limited bycold temperature, that is, at high latitudes and high eleva-tions A further benefit for crops may accrue in some semi-arid locations from increased precipitation, since a warmeratmosphere can hold more water vapor However, the locationand extent of any such regions of enhanced precipitation isnot known precisely, due primarily to the difficulty of simu-lating the regional-scale hydrological cycle in global climatemodels

A warmer and more variable climate is likely to havenegative as well as positive effects on agricultural regionsaround the world Potential negative effects include morefrequent droughts and floods, heat stress, increased outbreaks

of diseases and pests, shortening of crop growing periods, and

— in coastal regions — increased flooding and salination due

to sea-level rise and impeded drainage While the absolute

Figure 10.2 Agro-ecosystem processes and a changing climate

(Redrawn from Bongaarts, J 1994 Sci Am., 270:36–42.)

Carbon dioxide

fertilization

Longer growing season precipitationIncreased

Faster growing periods

Pest Heat stress

Increased flooding and salinization

magnitude of precipitation change in any one region or decade

is not predictable, global climate models project that logical regimes are likely to become more intense as well asmore variable (IPCC, 2001) Episodes of heat stress are known

hydro-to be detrimental hydro-to crops, especially during critical growthstages, and such episodes are likely to be more frequent andprolonged in the future

An important, albeit counterintuitive, negative effectthat warming has on crops is the shortening of their growingperiod (not their overall growing season) Warmer tempera-tures speed crops through their growing cycle, especially thegrain-filling stage Total yield is a product of the rate andduration of grain filling, which is determined by accumulatedtemperature Since higher temperatures shorten the duration

of grain filling, higher temperature tends to exert a negativepressure on the yield of most annual crops

Finally, in agricultural regions close to the ocean, level rise and associated saltwater intrusion and flooding canharm crops through impeded soil aeration and salination.This is likely to be most serious in countries such as Egyptand Bangladesh, which have major crop-growing areas in low-lying coastal regions

sea-10.4 WHAT WE HAVE LEARNED

10.4.1 Agriculture Regions Will Experience

Change over Time

Due to all the agro-ecosystem processes described above, it isfairly certain that agricultural regions will experience somechanges, and that these changes will evolve continuouslythrough the coming decades Shifts in crop zonation are likely

to occur, with some crop types expanding their ranges andothers contracting Given the range of projected temperatureand precipitation changes from global climate models, and theunknown degree of manifestation of direct CO2 effects oncrops growing in farmers’ fields, however, the magnitudes andrates of these changes are uncertain

The interactions between beneficial and detrimentalagro-ecosystem processes are likely to change over time forseveral reasons First, as biophysical responses move throughtheir temperature–response curves, responses to change intemperature may shift from positive to neutral, and then tonegative (Figure 10.3) Another reason that climate changeeffects are likely to be transformed over time is the potentialfor decadal shifts in the hydrological cycle While it is difficult

to predict the direction of change in any specific agriculturalregion, global climate models do show increased decadal vari-ability in hydrological regimes Finally, as crop breeding andpest species evolve in the coming decades under changingclimate conditions, new agro-ecosystem weeds, insects, anddiseases are likely to emerge, and the adjustment to thesemay be costly

Figure 10.3 Temperature response curve for biological processes

(From Rosenzweig, C., and D Hillel 1998 Climate Change and the

Global Harvest: Potential Impacts of the Greenhouse Effect on culture Oxford University Press, New York With permission.)

10.4.2 Effects on Agricultural Production

Systems Will Be Heterogeneous

Global studies done to date show that negative and positiveeffects will occur both within countries and across the world

In large countries such as the United States, Russia, Brazil,and Australia, agricultural regions will likely be affected quitedifferently (Figure 10.4) Some regions will experienceincreases in production and some declines (e.g., Reilly et al.,2003) At the international level, this implies possible shifts

in comparative advantage for export crop production Thisalso implies that adaptive responses to climate change willnecessarily be complex and varied

10.4.3 Agricultural Production in Many

Developing Countries Is Especially

Vulnerable

Despite general uncertainties about the rate and magnitude ofclimate change and about consequent hydrological changes,regional and global studies have consistently shown that

Figure 10.4 Simulated percentage changes in U.S regional cultural production, with adaptation, under the Canadian ClimateCenter scenario (From Reilly, J., F Tubiello, B McCarl, et al 2003

agri-Climatic Change, 57:43–69 With permission.)

Northeast Lake

states Cornbelt

North plains

Southeast Delta

South plains Mountain Pacific Appalachian

agricultural production systems in the mid and high latitudesare more likely to benefit in the near term (to mid-century),while production systems in the low latitudes are more likely

to decline (IPCC, 2001) In biophysical terms, rising tures will likely push many crops beyond their limits of optimalgrowth and yield Higher temperatures will create moreatmospheric water demand leading to greater water stress,especially in semi-arid regions Since most of the developingcountries are located in lower-latitude regions, while most devel-oped countries are located in the mid- to high-latitude regions,this finding suggests a divergence in vulnerability betweenthese groups of nations, with far-reaching implications forfuture world food security (Table 10.1) (Parry et al., 2004).Furthermore, developing countries often have fewerresources with which to devise appropriate adaptation mea-sures to meet changing agricultural conditions The combina-tion of potentially greater climate stresses and low adaptivecapacity in developing countries creates different degrees ofvulnerability as rich and poor nations confront global warm-ing This differential is due in part to the potentially greaterdetrimental impacts of a changing climate in areas that arealready warm, and in part to the generally lower levels ofadaptive capacity in developing countries The latter tend to

tempera-be food-recipient countries in times of food crises, while oped countries are more often donors

devel-Table 10.1 Effects of Climate Change on Global Food Production Under Various Scenarios (Percent Change in Yield)

HadCM3 2080s

HadCM2 2080s

10.4.4 Long-Term Effects on Agriculture Are

Negative

If the effects of climate change are not abated, even production

in the mid- and high-latitude regions is likely to decline inthe long term (end of 21st century) (Figure 10.5) Theseresults are consistent over a range of temperature, precipita-tion, and direct CO2 effects tested, and are due primarily tothe detrimental effects of heat and water stress as tempera-tures rise While the beneficial effects of CO2will eventuallylevel out, the detrimental effects of warmer temperatures andgreater water stress will be progressive in all regions

10.4.5 Agricultural Systems Can Adapt, but Not

Completely

Adaptation is integral to the study of climate change impacts

on agriculture Social scientists have made a significant tribution to the field of climate change impacts by bringingforward this important point (IPCC, 2001; Smith et al., 2003)

con-Figure 10.5 Generalized projection of world agricultural tion potential and areal extent under low and high CO2responsesfor increasing severity of climate change (Note: severity of climatechange may be taken as a proxy for decadal-to-century timeframe.)(From Fischer, G., and F Tubiello Personal communication, 2003.)

Production potential low CO 2 response

Production potential high CO 2 response

Area extent assuming low CO 2 response

Area extent potential assuming high CO 2 response

The task now is to integrate the findings and insights ofeconomists, sociologists, political scientists, anthropologists,and psychologists in providing guidance to decision makers,

so as to promote sectoral and international cooperation inminimizing the potential negative impacts and maximizingthe opportunities for adjustment to climate change

10.5 KEY INTERACTIONS

We need to understand how interactions within a changingclimate will affect agriculture (1) How will large-scale climatevariability systems such as the El Niño–Southern Oscillationchange? (2) How will supply and demand for water resources

be affected? (3) How will pests of crops and livestock — ing weeds, insects, and diseases — evolve?

includ-10.5.1 El Niño-Southern Oscillation

The El Niño–Southern Oscillation (ENSO) is a large-scaleocean–atmosphere, quasi-regular interaction in the PacificOcean, which has reverberations in the climate system world-wide These climate “teleconnections” bring droughts andfloods to many agricultural regions, especially in the tropics,but to some degree in mid-latitudes as well During an ElNiño event, droughts tend to occur in Northeast Brazil, Aus-tralia, Indonesia, and southern Africa, among other locations,while floods tend to occur in southeastern South America, thewest coast of North America, and the Horn of Africa

In the La Niña phase, the reverse tends to occur

for southeastern South America under the plentiful rainfallconditions of the El Niño in February 1998, and the severedrought brought on by the opposite La Niña conditions inFebruary 2000 While it is uncertain exactly how a warmingclimate will affect this major variability system, there ispotential for more frequent El Niño-like conditions that mayaffect agricultural regions around the world (IPCC, 2001)

Figure 10.6 shows the normalized difference vegetation index

Agriculture,

Niño, February 1998; La Niña, February 2000 (From W Baethgen, personal communication, 2003.)

February 2000 February 1998

Grupo de Riego y Agricultura Satelital

Grupo de Riego y Agricultura Satelital

© 2005 by Taylor & Francis Group, LLC

10.5.2 Water Resources

Both supply of and demand for water resources are likely tochange in a warming climate As population increases andurbanization proceeds apace, there is also likely to be greaterdemand for water from competing domestic and commercialusers Studies show that increased water requirements foragriculture in many regions are likely under warming condi-tions, and that there is potential for decadal “surprises” inthe reliability and percentage of water demand that can be

Research on water resources for agriculture in temperateareas has shown that changes in seasonality such as earliersnowmelt will likely change the filling and use of reservoirsand hence of water availability for irrigation (Figure 10.7b)(Strzepek et al., 1999) Current utilization plans for suchfacilities will need to be adjusted and readjusted as thedecades proceed Whereas early work on climate changeimpacts on agriculture tended to focus on the effects of morefrequent droughts, recent work has emphasized the importantrole of damage from floods and excess soil moisture as well(Figure 10.7c) (Rosenzweig et al., 2002) Early decades in thecentury may tend to be wetter and the later ones drier, due

to the greater effect of rising temperatures on evaporativedemand later in the century

10.5.3 Agricultural Pests

Pest–crop interactions play a crucial role in agro-ecosystems.Pest problems are very likely to be exacerbated under chang-ing climate conditions since pests tend to thrive in warmerconditions (Rosenzweig et al., 2001) This is due to the length-ening of the frost-free seasons, allowing for more generations

of pests; the extension of overwintering ranges with warmerwinters; and the potential for new pests to emerge andspread, such as has occurred with the soybean cyst nematode

and the soybean sudden death syndrome caused by Fusarium

mate, warmer temperature and increases in rainfall tend toincrease average per acre pesticide usage costs for manymet (Figure 10.7a) (Strzepek et al., 1999; Doll, 2002)

solani f sp alycines (Figure 10.8) Even in the current

cli-Figure 10.7 (A) Demand met (monthly average percentage of water demand met) and reliability (percentage of years in which water demands are met) for the Lower Missouri Water Region for the present and for the Max Planck (MPI) climate change scenario for the 2010s, 2020s, and 2050s (B) Runoff in the water regions supplying the U.S Cornbelt for current climate, and the Geophysical Fluid Dynamics Laboratory, MPI, and Hadley Center (HC) climate change scenarios (C) Number of events causing damage to maize yields due to excess soil moisture conditions, aver- aged over all study sites, under current baseline (1951–1998), and the HC and Canadian Climate Centre climate change scenarios Events causing a 20% simulated yield damage are comparable to the 1993 U.S Midwest floods (From Strzepek, K.M.,

D.C Major, C Rosenzweig, A Iglesias, D.N Yates, A Holt, and D Hillel 1999 J.

Am Water Resour Assoc., 35:1639–1655; and Rosenzweig, C., F.N Tubiello, R berg, E Mills, and J Bloomfield 2002 Global Environ Change, 12:197–202 With

crops (Chen and McCarl, 2001) The emergence of new pestscould produce situations for which agricultural systems maynot be prepared

10.6 MITIGATION AND ADAPTATION

RESPONSES

After nearly two decades of research on the potential impacts

of climate change on agriculture, attention is now turning to

Figure 10.8 Spread of agricultural pests under current climateconditions: (top) Spread of soybean cyst nematode, 1971-1998; (bot-tom) Spread of soybean sudden death syndrome (From Rosenzweig,

C., A Iglesias, X.B Yang, P.R Epstein, and E Chivian 2001 Global

Change Hum Health, 2:90–104 With permission.)

1998 1993 1985 1971

1998 1973

the assessment of appropriate responses A distinction can bemade between two types of responses: mitigation and adap-

tation Mitigation is action to check the rising atmospheric

concentration of greenhouse gases, thereby moderating their

effects Adaptation refers to actions that reduce the negative

effects or enhance the beneficial effects of climate changesthat are already occurring or are projected to occur in thefuture Adaptations may be either autonomous or planned(IPCC, 2001) Research on these two types of responses haveproceeded on parallel tracks Here we suggest that they beconsidered conjunctively

10.6.1 Mitigation

The practice of agriculture plays a major role in the global

Rosenzweig and Hillel, 2000) On a global scale, the process

of photosynthesis by agricultural crops fixes about 2 Gt Cyear–1, with about 1 Gt C year–1providing sustenance for theworld’s population that is respired back to the atmosphere as

it is consumed; about 1 Gt C is returned to the soil annually

as plant residues Some of the latter carbon, however, quently is returned to the atmosphere by soil microbial activ-ity, and some is stored in the soil matrix Furthermore, thefossil fuel that powers the machinery to sow, irrigate, harvest,and dry crops worldwide is responsible for atmospheric emis-sions of about 150 MT (million metric tons) C year−1 Largeamounts of fossil fuel energy are used to produce fertilizers,especially nitrogenous compounds Rice cultivation, livestockproduction, and soil processes are also responsible for consid-erable methane and nitrous oxide emissions (Rosenzweig andHillel, 1998)

subse-The agricultural carbon cycle offers several entry pointsfor mitigation of greenhouse gas accumulation in the atmo-sphere An important one is the potential for agricultural soils

to store carbon, particularly to the extent that its “active”carbon stores had been depleted by past soil managementpractices (Rosenzweig and Hillel, 2000) Other ways that agri-culture may help to mitigate the enhanced greenhouse effectcarbon cycle (Figure 10.9) (Rosenzweig and Tubiello, 2004;

are through the production of biofuels, the development ofmore efficient rice and livestock production systems, and thereduction of fossil fuel use by farm machinery.

10.6.2 Adaptation

Farmers have always had to adapt to the vagaries of weather,whether on weekly, seasonal, or annual timescales They willundoubtedly continue to adapt to the changing climate in thecoming decades, applying a variety of agronomic techniques,such as adjusting the timing of planting and harvesting oper-ations, substituting cultivars, and ultimately changing theentire cropping system

However, it is important to remember that farming tems have never been completely adapted even to the currentclimate (witness the recurrent effects of droughts and floods onvarious agricultural regions around the world) Hence, it seemsunreasonable to expect perfect adaptation in the future tochanging climate conditions Some adaptations will likely be

sys-Figure 10.9 The agricultural carbon cycle (From Rosenzweig, C.,and F Tubiello 2005 Accepted Mitigation and adaptation in agri-

culture: an interactive approach Mitigation and Adaptation

Strat-egies for Global Change With permission.)

1 GT C yr-1Cereal grain production

Residues

1 GT C y r-1

successful (e.g., change in planting dates to avoid heat stress),while other attempted adaptations (e.g., changing cultivars)may not always be effective in avoiding the negative effects ofdroughts or floods on crop and livestock production (Figure10.10) There are numerous social constraints to adaptation, as

Figure 10.10 Percent yield changes with and without adaptationunder the Canadian Climate Centre climate change scenario in the2030s Spring wheat with change of planting date (top) Winterwheat with change of cultivar (bottom) (From Tubiello, F Personalcommunication, 2003.)

well, some of which have been highlighted recently by socialscientists (Smith et al., 2003)

10.7 INTERACTIONS

The joint consideration of agricultural mitigation and tation is needed for several reasons Our research shows thatthe soil carbon sequestration potential of agricultural soilsvaries under changing climate conditions (Figure 10.11).Thus, a changing climate clearly will affect the mitigationpotential of agricultural practices If changing climate is nottaken into consideration, calculations such as those pertain-ing to carbon to be sequestered may be in serious error

adap-On the other hand, mitigation practices can also affectthe adaptation potential of agricultural systems For example,

by enhancing the ability of soils to hold moisture, carbonsequestration in agricultural soils helps crops withstand

Figure 10.11 Change in soil carbon in corn production undernitrogen fertilization and irrigation under current climate andunder the Canadian Climate Centre and Hadley Center climatechange scenarios (From Rosenzweig, C and F Tubiello 2005.Accepted Mitigation and adaptation in agriculture: an interactive

approach Mitigation and Adaptation Strategies for Global Change.

droughts and/or floods, both of which are projected to increase

in frequency and severity in a warmer climate Additionally,sequestering carbon in soil supports larger and more diversepopulations of microbes and other organisms that provideservices to plants and indirectly to animals, such as producingroot growth–promoting hormones All these functions can con-tribute substantially to the sustainability of agricultural sys-tems Adaptation practices may in turn affect the mitigationpotential For example, irrigation and nitrogen fertilizationmay greatly enhance the ability of soils in semi-arid regions

to sequester carbon

Finally, since it is likely that efforts to reduce theenhanced greenhouse effect (such as the Kyoto Protocol) willnot be completely effective, farmers and others in the agri-cultural sector will be faced with the dual tasks of reducingcarbon dioxide and other greenhouse gas emissions, whilehaving to cope with an already changing climate

10.7.1 Research Pathways

To better address the interactions between climate changeand sustainability of food and fiber production, we suggestthe following areas for future research attention

10.7.1.1 Climate Variability and Change

Another bifurcation in the field of climate impacts hasoccurred between research on responses to major systems ofclimate variability, such as between the El Niño–SouthernOscillation and long-term global warming The insights thathave been gained from studies of agriculture in regard tothese two timescales — seasonal to interannual vs decadal

to century — need to be reconciled

The work on seasonal-to-interannual climate forecastshas tended to focused on short-term decision making in regard

to predictions of El Niño and La Niña events, which aremanifested in terms of climate extremes The role of localstakeholders is crucial at these timescales, and responses arefocused on adaptation

The work on the decadal-to-century timescale, on theother hand, has focused primarily on responses to meanchanges and long-term decisions The stakeholders for climatechange impact studies have often been national policymakers.The goal here has usually been to provide information needed

to help these decision makers to decide long-term strategies

in regard to the climate change issue, in terms of both gation and adaptation

miti-New theoretical constructs are needed to link mate–agriculture interactions on the two timescales, as arenew ways to use analytic tools such as dynamic crop growthmodels and statistical analyses We need to move beyond themore tractable projections of crop responses to mean changes,and tackle the more difficult, yet more relevant, issue (tofarmers and agricultural planners) of how crops may respond

cli-to altered climate variability, such as changes in the frequencyand intensity of extreme events

10.7.1.2 Observed Effects of Warming Trends

Analysis of temperature records from around the world showsthat many regions are already experiencing a warming trend,

Warmer-than-normal springs have been documented in ern North America since the late 1970s (Cayan et al., 2001)

west-In some areas of the world, there have also been recent sodic increases in floods (e.g., North America) and droughts(e.g., Sahel) (IPCC, 2001), with likely but as yet mostly undoc-umented effects on food production The responses of agricul-tural systems to such changes need to be monitored anddocumented Have farmers indeed switched to earlier plant-ing dates? Have they changed cultivars? And are there anytrends in yields that can be discerned in conjunction with theclimate trends?

epi-Such questions are difficult to answer because other tors besides climate, such as land-use change and pollution,have been occurring simultaneously But they are importantfor furthering our understanding of agricultural adaptation

fac-to climate, and for validating the many simulation studiesespecially from the 1970s to the present (Figure 10.12)

done on potential climate change impacts in the future Theseanalyses will contribute to the IPCC Fourth Assessment nowunder way.

10.7.1.3 Global and Local Scales

of global and local/regional scales Recent work has sized the importance of scale in estimating the impacts ofclimate variability and change on agriculture (Mearns, 2003)

empha-In order to understand how a changing climate will affectagriculture, we must find new ways to bring detailed knowl-edge at local and regional scales to bear on global analyses

If we do not, our analyses may be in error

This is because agriculture in any one region is linked

to other agricultural regions, and indeed to the world foodsystem, both through trade and the food donor system As a

Figure 10.12 Observed temperature trends, 1970–2000 (FromNational Aeronautics and Space Administration/Goddard Institute

Temperature ( °C)

< –1.5 –1 –5 0 0 5 1 1.5 2 2.5> No data

for Space Studies http:///www.giss.nasa.gov/data/update/gistemp/

A final bifurcation that needs to be resolved is the reconciling

maps/)

changing climate shifts the comparative advantage in one ormore regions, other regions will inevitably be affected Thus,

in our research on agriculture and climate change, we need

to link regional “place-based” studies of vulnerability andadaptation, as well as mitigation, into a global synthesis

10.8 CONCLUSION

Improving responses to climate variability and change must

be a crucial requirement for future agricultural sustainability.The challenge for the field of climate change impacts on agri-culture is to integrate insights from the physical, biophysical,and social sciences into a comprehensive understanding ofclimate–agriculture interactions at seasonal-to-interannualand decadal-to-century timescales, as well as at regional andglobal spatial scales The final challenge is to disseminate andapply this knowledge to “real-world” agricultural practicesand planning worldwide, so that long-term sustainability may

be truly enhanced

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11

Assessing the Consequences of Climate Change for Food Security: A View from the Intergovernmental Panel on Climate

ChangeWILLIAM EASTERLING

CONTENTS

11.1 Introduction 27011.2 State of the Global Agriculture Sector 27111.2.1 State of Agriculture 27211.3 Environmental Pressures on Agriculture 27311.4 Response of Agriculture to Rising Atmospheric

CO2 and Climate Change 27411.4.1 Direct Effects of Rising Atmospheric CO2 274

11.4.1.1 CO2 Effects on Crops 27411.4.2 Impacts of Climate Change 275

11.4.2.1 Impacts on Crops and Livestock 27511.4.3 Response and Adaptation to Impacts on

Crops, Livestock, and Forest Resources 280

11.4.3.1 Response and Adaptation of

Crops and Livestock 28011.5 Summary and Conclusions 28511.5.1 State 28511.5.2 Pressure 28511.5.3 Response 28511.5.4 Adaptation 286Acknowledgments 287References 287

11.1 INTRODUCTION

Considerable progress in understanding how global climatechange is likely to affect agricultural production and forestresources has been made in recent years In the recent ThirdAssessment Report (TAR) of the Intergovernmental Panel onClimate Change’s (IPCC) Working Group (WG) II (IPCC,2001), agriculture was combined in a chapter with other, lessmanaged terrestrial and aquatic ecosystems in order to assessits response to climate change This was intended to facilitatecomparison of the impacts of climate change on basic biolog-ical and ecological processes across ecosystems (includingagroecosystems and forest ecosystems) in a consistent man-ner However, agroecosystems are fundamentally differentfrom less managed ecosystems such as wetlands, tundra, andsavannas: they produce economically valuable goods and ser-vices within a system of clear and enforceable property rights.Such greatly complicates understanding of their response toclimate change because of intense human intervention intoclimate–ecosystem interactions and because responses ofthese ecosystems to climate change can have direct and imme-diate economic impacts Hence, I focus on agriculture in thischapter

The aim of this chapter is to distill important insightsinto the vulnerability, potential impacts, and adaptation pros-pects of agriculture in response to climate change from theIPCC’s WG II TAR Most of the discussion here is drawn frommaterial generated for chapter 5 and reported in Easterling

and App (in press) The purpose of that chapter was to reviewand assess scientific progress in understanding of how eco-systems (including agroecosystems) and their coupled socialsystems may respond and adapt to climate change, and toprovide a global perspective on possible agricultural out-comes We recognize the importance of understanding small-scale regional variation in such outcomes, but leave detaileddiscussion of such for others to consider.

We follow a modified version of the response model (to include adaptation) of the Organizationfor Economic Cooperation and Development (OECD) to report

state-pressure-key findings State refers to the status or condition and future

trends in food, fiber, fuel, and fodder systems under current

climate conditions Pressure refers to environmental and

social stresses, including those arising from climate change,

on such systems Response refers to the induced changes in

these systems arising from the imposed pressures (including

climate change) Adaptation refers to the managed changes

in ecosystems and deliberate human actions aimed at ing to climate change This model disciplines our synthesis ofthe large amount of research on the consequences of climatechange by focusing the review on the following questions:What is the current state of the Earth’s agricultural ecosys-tems, and how effectively are we meeting the demands fortheir goods and services? What major challenges confront theworld’s food and fiber sectors over the next several decades,whether the climate changes or not? What are the likelybiophysical and socioeconomic effects of climate change? Whatare the prospects for successful adaptation by agriculturalsystems to those effects? How vulnerable will those systems

adjust-be after accounting for the potential for adaptation to alleviatestress or take advantage of opportunity?

11.2 STATE OF THE GLOBAL AGRICULTURE

SECTOR

Agriculture and forests account for approximately 41% of theEarth’s land covers (Houghton, 1990) According to the UnitedNation’s Food and Agriculture Organization (FAO)

bal exports of their commodities and services were valued at

$440 billion in 1999 As noted above, unlike less managedecosystems, the products of agriculture and forests are traded

as commodities on world markets Those products possesscritical life-giving properties and are part of the Earth’s lifesupport system There is a consensus that the global food andfiber enterprise will be challenged over the coming decades

to expand capacity in step with anticipated expansion in bal demand (World Bank, 1993; Alexandratos, 1995; Roseg-rant et al., 1995; Antle et al., 1999; Johnson, 1999).Furthermore, the most severe challenge to the ability of globalagricultural capacity to expand space with demand, with orwithout climate change, will come in the next 25 to 40 years,with the challenge abating after that, as population growth

glo-is projected to slow and global income elasticity of fooddemand is projected to decline That is, the real story ofclimate change impacts on global agriculture is likely to beplayed out over the next 25 to 40 years, with the rest of thecentury being anticlimactic

11.2.1 State of Agriculture

Agricultural production in the latter half of the 20th centuryincreased, with the global food supply outstripping theincrease in global demand for food; this was accomplished inspite of increases in global population and incomes As aresult, prices for most major crops declined when adjusted forinflation Wheat and feed corn declined at an annual averagerate of 1% to 3% over the period (Johnson, 1999; Antle et al.,1999) In the absence of climate change, several analysts (e.g.,World Bank, 1993; Rosegrant et al., 1995; Johnson, 1999)expect inflation-adjusted food prices to remain stable or slowly

to decline over the next two decades Confidence in this come is high over the next two decades

out-Declining food prices will likely ease but not fully eraseproblems of food security, particularly in low-income countrieswhere lack of access to food, political instability, and inade-quate physical and financial resources will remain major

glo-challenges In some instances, especially in the small number

of nations with little immediate prospect for a successfultransition from agricultural economies to manufacturing orservice-based economies, lower global food prices could bestressful However, the anticipated spread of technology andscience-based production practices even to the poorest agri-cultural economies will likely reduce costs of production tohelp farmers cope with lower prices Agricultural trade poli-cies tend to decrease the efficiency of production both in high-and low-income countries In high-income countries, policiestend to subsidize production in order to protect the agriculturesector, while in low-income countries policies tend to tax anddiscourage production (Schiff and Valdez, 1996)

Much of the optimism for future growth in agriculturalproduction hinges on anticipated technological progress thatincreases crop yields Rosegrant and Ringler (1997) argue thatconsiderable unexploited capacity to raise crop yields exists

in current crop varieties Other analysts (Pingali, 1994;Tweeten, 1998) argue that the declining supply of new agri-cultural land combined with large-scale degradation of soiland water resources will slow the increase in global agricul-tural output, which may slow or negate the expected decline

in real food prices Approximately 50% of cereal production

in developing countries is irrigated and, although it accountsonly for 16% of the world’s crop land, irrigated land produces40% of the world’s food It appears that the rate of expansion

of irrigation is slowing, and 10% to 15% of irrigated land isdegraded to some extent by waterlogging and salinization(Alexandratos, 1995) It is questionable whether irrigationwater supplies necessary to meet future irrigation demandswill be available The two conflicting views represented in thisparagraph make the future trend in prices beyond the firstthird of the century highly uncertain

11.3 ENVIRONMENTAL PRESSURES ON

AGRICULTURE

The degradation of environmental assets, especially soils, air,and water, severely challenges the productivity of agriculture

and forest resources (Pinstrup-Andersen and Pandya-Lorch,1998; Price et al., 1999a, 1999b) In the post–World War IIperiod, approximately 23% of the world’s agricultural andforest lands were classified as degraded by the U.N Environ-ment Programme (Oldeman et al., 1991) Irrigated land isparticularly vulnerable, although the expansion of irrigation

is slowing

Although the economic impacts of the long-term mental degradation of forest and agricultural systems aredifficult to determine, the general consensus is that they willeventually begin to undermine the necessary expansion offood and fiber production if allowed to increase at currentrates

environ-11.4 RESPONSE OF AGRICULTURE TO RISING

ATMOSPHERIC CO 2 AND CLIMATE

CHANGE

11.4.1 Direct Effects of Rising Atmospheric CO 2

11.4.1.1 CO2 Effects onCrops

Results from experimental studies have established that it is

no longer realistic to examine the effects of climate change

on crop and forage plants without also accounting for thedirect effects of rising atmospheric CO2 at the same time Theshort-term responses to elevated CO2 of isolated plants grown

in artificial conditions remain difficult to extrapolate to crops

in the field (Körner, 1995) Even the most realistic free-aircarbon dioxide enrichment (FACE) experiments yet under-taken impose an abrupt change in CO2 concentration andcreate a modified area (Kimball et al., 1993) analogous to asingle irrigated field in a dry environment Natural ecosys-tems and croplands are experiencing a gradual increase inatmospheric CO2 Nonetheless, a cotton crop exposed to FACEincreased biomass and harvestable yields by 37% and 48% inelevated (550 ppm) CO2 (Mauney et al., 1994) At the same

CO2 increase, spring wheat yields increased by 8% to 10%when water was nonlimiting (Pinter et al., 1996) A simple

linear extrapolation of spring wheat FACE results to a bling of CO2 produces a 28% increase in yields.

dou-Several important breakthroughs in the understanding

of how direct effects on crops via CO2 were accomplished sincethe Second Assessment Report (SAR) Most concern improve-ments in the understanding of how climate interacts with thephysiology of CO2 direct effects Horie et al (2000) found thatmoderate temperatures accompanied by a doubling of CO2increases the seed yield of rice by 30% However, with each

1°C increase in temperature above 26°C, rice yields declined

by 10% because of shortened growth period and increasedspikelet sterility This raises concerns that CO2 benefits maydecline quickly as temperatures warm (established but incom-plete) On the positive side, crop plant growth may benefitmore from CO2 enrichment in drought conditions than in wetsoil because photosynthesis would be operating in a moresensitive region of the CO2 response curve (Samarakoon andGifford, 1995) Significantly, this effect was observed in C4photosynthesis The most likely explanation for this thus far

is that drought-induced stomatal closure causes CO2 tobecome limiting in the absence of CO2 enrichment (estab-lished but incomplete) It is not clear how much this effect islikely to offset the overall effect of drought on crop yield Also,the notable dearth of testing of tropical crops and suboptimalgrowth conditions (nutrient deficits, weed competition, patho-gens) continues from the SAR as a major research gap

11.4.2 Impacts of Climate Change

11.4.2.1 Impacts on Crops and Livestock

Major advances were made since the SAR in the ing of how changes in climate elements such as temperature,precipitation, and humidity, are likely to affect crop plantsand livestock; CO2 direct effects were included in much of thisnew crop research A review of 43 crop modeling studies per-formed since the SAR revealed important geographic differ-ences in the predicted impact of climate change on yields(Gitay et al., 2001, Table 5.3) The studies incorporated a widerange of climate change scenarios, including several different

understand-general circulation model experiments, historical climate tuations, and simple sensitivity experiments While change

fluc-in climate variability, deffluc-ined as change fluc-in the highermoments of climate elements, was not explicitly examined inthis part of our review, it is incorporated in many of thescenarios used in the crop modeling experiments The model-ing studies were separated into tropical and temperateregions for comparison Predicted percentage changes inyields (relative to current yields) in response to climatechange from each study were plotted against local tempera-ture increases; the crops were rice and corn in the tropics,and corn and wheat in the temperate regions All studiesaccounted for CO2 direct effects but not for adaptation Onlystudy results based on local precipitation increase wereselected for this comparison We focused on cases of precipi-tation increase for three reasons: (1) to permit evaluation ofthe response of crops to the least stressful expected conditions

as a conservative estimate of crop sensitivity; (2) to be able

to report an acceptable number of studies performed withcomparable climate change characteristics — there are moremodeling studies in important agricultural regions based onpositive precipitation change than negative; and (followingfrom 2) (3) among the more discernable patterns of agreementamong climate model projections reported by the TAR-WG II(Carter and LaRovere et al., 2001) are increases in summerprecipitation in high northern hemisphere latitudes, tropicalsouthern Africa, and south Asia, with little change in south-east Asia (Continental drying can be expected even whenwarming is accompanied by increased precipitation due to theeffects of higher evapotranspiration.) The distribution of rawmodeled yields vs temperature change was converted to a lognormal distribution in order to damp the distorting effect ofoutlier yield estimates The logged yield values were thenwere averaged across studies at each degree of temperaturechange — that is, yield estimates for all studies reported at,for example, +1°C were averaged to create a mean value for+1°C, +2°C, and so on out to +4°C The mean log yields werethen converted back to their original units (MT−ha) and plotted

to produce the line graphs shown in Figures 11.1 and 11.2

relatively greater sensitivity of tropical crops to climatewarming than temperate crops In the tropics, although riceyields increase by approximately 7% above current yields with1°C of warming, they decline sharply beginning at 2°C ofwarming, falling to 17% below current yields at the maximum

of 4°C of warming The initial positive response of rice washeavily skewed by a preponderance of studies at the northernedges of the tropics Rice yields everywhere else in the tropicsdeclined with the initial 1°C of warming Tropical corn yieldsdecline by nearly 7% with the initial 1°C of warming, by morethan 20% with 4°C of warming This will pose a challenge toadequate food production in a majority of the world’s leastdeveloped nations

In temperate regions, corn was slightly benefited bywarming of up to 2°C of warming before slipping below cur-rent yields at +3°C (Figure 11.2) Wheat yields tended to beless resilient in response to the climate change, slipping belowcurrent yields at +2°C, and declining to 25% below currentyields at +4°C

Figure 11.1

tropics averaged across 13 crop modeling studies All studiesassumed a positive change in precipitation CO2 direct effects wereincluded in all studies

Temperature °C

Corn Rice

Corn and rice yields vs temperature increase in the

Comparison of Figures 11.1 and 11.2 demonstrates the

The greater sensitivity of tropical crops to warming ispartly explained by the fact that crops there are grown undernormal temperatures that approach theoretical optima forphotosynthesis, and any additional warming is deleterious,even when accompanied by increased precipitation Temper-ate crops are normally cold temperature limited, and the earlystages of warming, accompanied by increasing precipitation,undoubtedly stimulate higher productivity — for a while.However, as temperate warming proceeds, so does evapotrans-piration At temperature increases of +3°C or greater, evapo-transpiration appears to overcome the benefits of warmingand increased precipitation, leading to increasing aridity anddecreasing yields Hence, all major planetary granaries arelikely to require adaptive measures by +2°C to 3°C of warming

no matter what happens to precipitation It would be able to expect adaptive measures to become necessary atlesser amounts of warming in those regions experiencing pre-cipitation decreases with the warming

reason-Recent research on the impact of climate change directly

on livestock supports the major conclusions of the SAR.Farm animals experience climate change directly by altered

Figure 11.2 Corn and wheat yields vs temperature increase inthe temperate zone averaged across 30 crop modeling studies Allstudies assumed a positive change in precipitation CO2 directeffects were included in all studies

Temperature °C

Corn

Wheat -5

physiology and indirectly by changes in feed supplies A dearth

of physiological models that relate climate to animal physiologylimits confidence in predictions of impacts, although modelbuilding is underway (Hahn, 1995; Klinedinst et al., 1993) How-ever, there is general consensus from experimental results thatclimate warming likely will alter heat exchanges between ani-mals and their environment such that mortality, growth, repro-duction, and milk and wool production would be affected.Livestock managers routinely cope with weather and cli-mate stresses on their animals, using techniques such asstrategic shading and use of sprinklers This bodes well foradapting to climate change

11.4.2.1.1 Accounting for Climate

Variability

Natural climate variability and its changes with mean ing regulate the frequency of extreme events such as drought,excessive moisture, heat waves, and the like, which are criticaldeterminants of crop and livestock production Carter and

warm-LaRovere et al (2001) list several likely to very likely changes

in extreme events of importance to agriculture including, forexample, higher maximum temperatures over nearly all landareas and increased summer drying over most mid-latitudecontinental interiors (even in cases of increased precipitationdue to increased evapotranspiration) Research has onlybegun to consider the effect of change in frequency of extremes

on agricultural production explicitly Some analysts find thatincreased interannual climate variability accompanyingmean climate changes disrupts crop yields more than meanclimate changes alone (Mearns et al., 1995; Rosenzweig et al.,2000) Stochastic simulations of wheat growth indicated that

a greater interannual variation of temperature reduces age grain yield more than a simple change in mean temper-ature The potential of a change in extreme events withclimate change to amplify the impact of climate change oncrop productivity (both positively and negatively) is estab-lished but research is incomplete

aver-Analysts argue that it is important that the effect ofchange in climate variability on crops be distinguished fromthat of the change in mean climate conditions as a basis fordistinguishing the impacts of natural swings in climate vari-ability from those of climate change Hulme et al (1999) found

it difficult to distinguish the impact on modeled wheat yield

of simulated natural climate variability from that of lated changed variability due to climate change Hulme et al.(1999) compared wheat yields simulated with a multi-centurymodeled control climate containing realistic natural climatevariability with those simulated with a multi-century climatechange containing a change in climate variability They foundthat yields under the control climate were indistinguishablefrom yields under climate change in a majority of the model-ing sites Such simulation results emphasize the need forgreater efforts to distinguish the “noise” of natural climatevariability from the “signal” of climate change (Semenov etal., 1996)

simu-11.4.3 Response and Adaptation to Impacts on

Crops, Livestock, and Forest Resources

11.4.3.1 Response and Adaptation of Crops

and Livestock

The impacts of climate change will induce responses fromfarmers and ranchers aimed at adapting Initial responseslikely will be autonomous adjustments to crop and livestockmanagement such as changes in agronomic practices (e.g.,earlier planting, cultivar switching) or microclimate modifi-cation to cool animals’ environment They require little gov-ernment intervention and are likely to be made within theexisting policy and technological regimes Methodologically,there has been little progress since the SAR in modelingagronomic adaptations On the positive side, the adaptationstrategies being modeled are limited to a small sample of themany possibilities open to farmers, which may underestimateadaptive capacity On the negative side, the adaptations tendunrealistically to be implemented as though farmers possessperfect knowledge about evolving climate changes, which may

overstate their effectiveness (Schneider et al., 2000) The ponderance of studies finds agronomic adaptation to be mosteffective in mid-latitude developed regions and least effective

pre-in low-latitude developpre-ing regions (Parry et al., 1999; zweig and Iglesias, 1998) However, differences in assump-tions and modeling methodology among studies often lead toconflicting conclusions in specific regions For example, in twostudies using the same climate change scenarios, Matthews

Rosen-et al (1997) simulate large increases while Winters Rosen-et al.(1999) simulate large decreases in rice yield with adaptationacross several countries in Asia This lowers confidence inthese simulations

Like crop producers, livestock managers are likely toimplement routinized adaptive techniques that were devel-oped to deal with short-term climate variability during theinitial stages of warming For example, Hahn and Mader(1997) suggest several proactive management countermea-sures that can be taken during heat waves (e.g., shades and/orsprinklers) to reduce excessive heat loads The success live-stock producers have had in the past with such countermea-sures gives optimism for dealing with future climate change.However, coping can entail significant dislocation costs forcertain producers Confidence in the ability of livestock pro-ducers to adapt their herds to the physiological stresses ofclimate change is difficult to judge As noted above, theabsence of physiologically based animal models with well-developed climate components suggests a major methodolog-ical void

11.4.3.1.1 Economic Costs of Agricultural

Adaptation

The agricultural cost (both to producers and consumers) ofresponding to climate change will mostly be for the imple-mentation of measures to adapt (See referred Gitay et al.,

2001, Table 5.3 for details of climate scenarios used in modelsimulations reported in this section.) At the individual farm

or ranch level, these costs will reflect changes in revenues,while at national and global levels they will reflect changes