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OCR for page 5960
Proc. Natl. Acad. Sci. USA
Vol. 96, pp. 5960-5967, May 1999
Colloquium Paper
This paper was presented at the National Academy of Sciences colloquium "Plants and Population: Is There Time?"
held December 5-6, 1998, at the Arnold and Mabel Beckman Center in Irvine, CA.
The transition to agricultural sustainability
VERNON W. RUTTANa
Departments of Applied Economics and Economics, University of Minnesota, St. Paul, MN 55108
ABSTRACT The transition to sustainable growth in ag- A second approach employed in attempts to reach beyond
ricultural production during the 21st century will take place the analytical constraints of the more formal integrated models
within the context of a transition to a stable population and has been to construct plausible scenarios of alternative devel
a possible transition to a stable level of material consumption. opment paths that could arise from the forces that will drive
If the world fails to successfully navigate a transition to the world system across the 21st century. Scenarios are stories
sustainable growth in agricultural production, the failure will told in the language of words as well as numbers. There are
be due more to a failure in the area of institutional innovation usually four major steps in formulating a scenario (94. The
than to resource and environmental constraints. current state of the system is first described and quantitatively
represented in sufficient detail to clarify the key issues that will
be addressed. Next, the "driving forces" that govern the system
and move it forward are identified and characterized. A third
step involves identifying the forces that can redirect beliefs,
behaviors, and policies away from some visions of the future
toward others. Finally, an attempt can be made to impose
surprising events on the scenario trajectory.
Recent examples include the World Resources Institute
Santa Fe Institute-Brookings Institution "2050 Project" (2)
and the Stockholm Environmental Institute (3~. The Stock
holm group presented three basic scenarios: Conventional
Worlds, Barbarization, and Great Transitions (Fig. 1~.
Conventional Worlds. The Conventional Worlds Reference
Scenario assumes that economic trends will, with minor vari
ations, continue along the historical trajectory of the 20th
century without fundamental changes in institutions and val
ues. "These include markets, private investment, and compe
tition as the fundamental engine for economic growth and
wealth allocation; free trade and unrestricted capital and
financial flows to foster globalization of product and labor
markets, rapid industrialization and urbanization; possessive
individualization as.... the basis of the 'good life'; and the
nation-state and liberal democracy as the appropriate form of
governance...." (ref. 10, p. 3~.
The Reference Scenario implies a kinder and gentler world
than projected in Limits to Growth. Population increases from
~6 billion to a peak of ~10 billion in 2050 with nearly all the
increase in the presently poor countries. The economies of the
developing countries grow more rapidly than those of the
developed (Organization for Economic Cooperation and De-
velopment) countries 3.6 as compared with 2.0% per year.
The ratio of per capita gross domestic product between the rich
Organization for Economic Cooperation and Development
countries and the rest of the world declines from 20 in 1990 to
15 in 2050 but the absolute difference continues to widen.
Structural shifts in economic activity from agriculture to
industry to services continues. Trends toward dematerial-
ization and decarbonization also continue. Although energy
use grows far less rapidly than gross domestic product, due to
The institutional and cultural foundations of the modern world
began to emerge in Western Europe in the 17th and 18th
centuries. The material basis for the agricultural and industrial
revolutions was established during the 18th and 19th centuries.
These advances were initially limited to a few countries in
western Europe and their offshoots. For most countries of the
world, the transition did not begin until well into the 20th
century. These institutional and technical changes combined to
generate unprecedented growth in population, in resource use,
and in human welfare. Since mid-century alone, global pop-
ulation has doubled, energy production has more than tripled,
and economic output has increased by a factor of five.
The challenge of the 21st century will be to make the
transition to sustainable growth in both presently developed
and low income countries. It will involve a transition to a stable
global population, it may involve a transition to a stable level
of material consumption, and it will involve a transition to a
largely urban society. Whether the transition will be accom-
panied by levels of material and energy consumption in
presently poor countries comparable to the levels that have
been achieved by the industrial countries is the subject of
intense debate. How much land will be left to nature after
meeting the demands for agricultural commodities and the
demands for environmental services arising out of population
and income growth is even more problematical.
SUSTAINABILITY SCENARIOS
It will be useful to discuss the transition to agricultural
sustainability within the context of broader visions of global
sustainability.b One thing we can be certain of is that, in the
future, we will be continuously confronted by surprise. One
approach to the exploration of plausible futures is the con-
struction of integrated assessment models. An early, and highly
controversial, example was the Club of Rome's report on
Limits to Growth (~64. The report depicted a world entering an
"era of limits" in which even low rates of growth would no
longer be sustainable. More recent integrated assessment
models have emphasized the specification of more realistic
model structures and parameter values. There also has been a
shift away from prediction and toward exploration of the
sensitivity to alternative parameter values and policy regimes.
Integrated assessment models are increasingly employed in
addressing global climate change issues (7, 8~.
PNAS is available online at www.pnas.org.
Abbreviation: DDT, dichlorodiphenel-trichloroethane; IPM, inte-
grated pest management.
aTO whom reprint requests should be addressed. e-mail:
vruttan@dept.agecon.umn.edu.
bIn this section, I draw on my participation in the work of the NRC
Board on Sustainable Development and its report, Our Common
Journey: Toward a Sustainability Transition (~14. See also Hammond (2)
and Raskin et al. (~3~. For the evolution of the concept of sustain-
ability, see Lele (4) and Ruttan (5~.
5960
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Colloquium Paper: Ruttan
Class
Vanant
Conventional Worlds
Reference
Policy Reform
Proc. Natl. Acad. Sci. USA 96 (1999) 5961
.
~ ~ >~ ~ :
Economy Environment Equity Technology Conflict
,
\ \
/
~/1
1~ ~
/
/
FIG. 1. Archetypal scenarios with illustrative patterns of change. The scenario structure shows sketches of behavior over time for six descriptive
variables: population growth, economic scale, environmental quality, socioeconomic equity, technological change, and degree of social and
geopolitical conflict. The curves are intended as rough illustrations of the
Environment Institute.
structural and technological changes, the greater scale of
human activity results in rising environmental stress on the
assimilative capacity of the air, water, and soil. Oil and gas
become increasingly scarce, but price increases are contained
by development of backup technologies.
The world described by the Reference Scenario is richer but
dirtier than the world we live in at the threshold of the 21st
century! There are also substantial risks associated with the
Reference Scenario. "First, the cumulative loads on Earth's
geochemical cycles and ecosystems could exceed natural as-
similative capacities.... Second, heightened pressure on nat-
ural resources could lead to economic and social disruptions or
even conflicts".... (ref. 9, p. 11~. The persistence of poverty
in poor resource countries experiencing rapid population
growth could become a serious source of social, political, and
economic stress.
These concerns lead to construction of a Policy Reform
variant of the Conventional Worlds Scenario. The Policy
Reform variant assumes that, within the context of current
values and institutional structures, governments act vigorously
to achieve rapid economic growth, greater distributional eq-
uity, and serious protection of environmental quality. The
policy reform variant would require major institutional
changes, including substantial transfer of resources from rich
to poor countries, and major technological changes, including
a more rapid shift toward dematerialization and decarboniza-
tion than implied in the Reference Scenario. It would also
require a more active public role in environmental manage
possible patterns of change only. Figure is courtesy of the Stockholm
meet. The benefits, as compared with the Reference Scenario,
would be realized in terms of improvements in environmental
quality, greater equity, and a reduction in sociopolitical con-
flict (Fig. 1~.
Fundamental Change. The Stockholm Environmental In-
stitute studies present two alternative scenarios, each with two
variants, that assume more fundamental changes. In the Great
Transitions New Sustainability variant, governance and eco-
nomic systems reflect a stronger sense of global community
and place a higher value on environmental amenities. The flow
of energy and material through the economy is drastically
reduced even as incomes continue to rise. Incomes in the
poorer regions of the world converge more rapidly toward
those in the developed countries. Growth in cultural consump-
tion emerges as a substitute for growth in material consump-
tion. This new postindustrial culture can only emerge from
successful efforts to design the technical and institutional
changes that will be necessary to respond to challenges that will
be confronted in attempting to provide an improved quality of
life for the people who will be living in the increasingly
urbanized world.
The Barbarization Scenarios arise out of failure to realize
the institutional reforms necessary to achieve either the Con-
ventional Worlds or the Great Transitions scenarios. "The
most significant element of these scenarios is that the number
of people living in poverty increases while the gap between rich
and poor grows both within and among countries" (ref. 9, p.
26~. Local and regional environments come under increasing
OCR for page 5962
5962 Colloquium Paper: Ruttan
stress, and conflict over access to natural resources intensifies.
The Breakdown and Fortress World variants differ primarily in
the degree to which the prevailing power structure-
governments, transnational corporations, international orga-
nizations, and the armed forces manages to maintain some
semblance of order.
SCIENTIFIC AND TECHNICAL CONSTRAINTSC
The half-century since World War II has experienced unprec-
edented rates of growth in population, in per capita income,
and in agricultural production. World population increased
from 2.5 billion in 1950 to ~6.0 billion in the late l990s. The
global annual population growth rate peaked at slightly >2.0%
in the mid- to late 1960s (11~. The production of cereal crops
more than tripled during the same period. In spite of rapid
population growth, global average per capita food availability
rose from 2,700 calories. Projections of future
population and income growth are notoriously uncertain.
Population growth will likely add 3.0-5.0 billion people to
world population by 2050. The contribution of income growth
to growth in food demand will depend importantly on whether
the decline in the rate of per capita income growth in the low
and middle income countries since 1980 is reversed in the early
years of the 21st century. While income growth in rich
countries imposes very little burden on per capita food con-
sumption, the very poor often spend as much as one half of any
increase in per capita income on food.
In the l950s and 1960s, it was not difficult to anticipate the
sources of the increase in agricultural production over the next
several decades. Advances in crop production would come
from expansion in irrigated area, from more intensive appli-
cation of fertilizer and crop protection chemicals, and from the
development of crop varieties that would be more responsive
to fertilizer and management. Advances in animal production
would come from genetic improvements and advances in
animal nutrition. At a more fundamental level, increases in
grain yields would occur from changes in plant architecture
that would make possible higher plant populations per hectare
and by increasing the ratio of grain to total dry matter.
Increases in production of animals and animal products would
come about by decreasing the proportion of feed devoted to
animal maintenance and increasing the proportion used to
produce usable animal products.
I find it much more difficult to tell a convincing story about
the sources of increase in crop and animal production over the
next half-century than it was a half-century ago. There are
severe physiological constraints to increasing the grain-to-dry-
matter ratio or to reducing the percentage of animal feed
devoted to animal maintenance.0 These constraints will im-
pinge most severely in those areas that have already achieved
the highest levels of output per hectare or per animal unit in
western Europe, North America, and East Asia. The con-
straints are already evident in terms of a reduction in the
incremental yield increases from fertilizer application and
smaller incremental reductions in labor input from the use of
larger and more powerful mechanical equipment.
There are also preliminary indications of declines In agr~-
cultural research productivity. As average grain yields, under
favorable conditions, have risen from the 1.0-2.0 to the 6.0-8.0
metric-tons-per-hectare range, the share of research budgets
devoted to maintenance research the research needed to
maintain existing crop and animal productivity levels has
risen relative to the total research budget (12~. As a result, the
scientist years required to achieve incremental yield increases
CIn this and the following sections, I focus primarily on supply side
constraints, in contrast to the paper by Johnson (65), which empha-
sizes demand side constraints on agricultural production.
See the papers by Cassman (66) and Sinclair (59~.
. .
Proc. Natl. Acad. Sci. USA 96 (1999)
in wheat and maize have been rising more rapidly than the yield
increases (13~. And the cost per scientist has been rising more
rapidly than the general price level (14, 15~. I find it difficult
to escape a conclusion that agricultural research, in the
countries that have achieved the most rapid gains in agricul-
tural technology over the last half-century, has begun to
experience diminishing returns to both public and private
sector agricultural research. The good news is that there
remains a substantial gap between the more technically ad-
vanced regions and the lagging regions that can be narrowed
if sufficient effort is devoted to adaptive research and diffu-
s~on.
It is possible, within another decade, that advances in
molecular biology and genetic engineering will reverse the
urgency of the above concerns. The use of genetic engineering
is enabling plant breeders to manipulate genetic materials with
greater precision and to speed the pace of crop breeding. The
applications of genetic engineering that are presently available
in the field, however, are primarily in the area of plant
protection and animal health. They are enabling producers to
push crop and animal yields toward their genetic potential, but
they have not yet raised the biological ceilings above the levels
that have been achieved by researchers employing the older
methods based on Mendelian biology.e The advances that are
most likely to be introduced over the next decade are likely to
be the result of efforts to realize higher value added as in
neutraceuticals and pharmaceuticals rather than from ef-
forts to break the constraints on yield ceilings. The excessively
broad patent rights being granted in the field of biotechnology
may become a serious institutional constraint on the transfer
of plant protection and animal health biotechnology products
to farmers in developing countries.
RESOURCE AND ENVIRONMENTAL
CONSTRAINTS
A second set of concerns about the capacity of the agricultural
sector to respond to the demands that will be placed on it
focuses on resource and environmental constraints. Part of this
concern is with the feedback of the environmental impacts of
agricultural intensification on agricultural production itself.
These include the degradation and loss of soil resources due to
erosion, the water logging and salinity associated with irriga-
tion, the convolution of pests and pathogens associated with
use of chemical controls, the impact of global climate change,
and the loss of biological diversity.
Soil Erosion. Soil erosion and degradation have been widely
regarded as a major threat to sustainable growth in agricultural
production both in developed and developing countries (18-
20, 22~.f It has been projected to become an even more severe
constraint into the future (22~. It has been suggested, for
example, that, by 2050, it may be necessary to feed "twice as
many people with half as much topsoil" (ref. 23, p. 115.
Attempts to assess the implications of erosion on agricul-
tural production confront serious difficulties. Water and wind
erosion estimates are measures of the amount of soil moved
from one place to another rather than the soil lost to agricul-
tural production. Most studies do not provide the information
necessary to estimate yield loss from erosion and degradation.
eSeveral students have presented more optimistic perspectives. See' for
example Waggoner (16). I find it somewhat surprising that I find it so
difficult to share the current optimism about the dramatic gains to be
realized from the application of molecular genetics and genetic
engineering. My first major professional paper was devoted to refut-
ing the pessimistic projections of the early and mid-19SOs (17).
fLand degradation is a broader concept than erosion. It includes areas
affected by soil degradation; drylands with vegetation degradation but
no soil degradation; and degraded moist tropical forest lands (21).
gFor a very useful introduction to the issues discussed in this section
see the exchange between Crosson (24, 25) and Pimentel et al. (26).
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Colloquium Paper: Ruttan
Even in the United States, credible national soil erosion
measures are available only for three years (1982, 1987, and
1992~. These studies, conducted by the U.S. Department of
Agriculture Soil Conservation Service, now the Natural Re-
sources Conservation Service, indicate that the rate of soil
erosion had declined by 24% between 1982 and 1992, presum-
ably because some 30-35 million acres of highly erosive land
was put in the Conservation Reserve. Only the 1982 studies
included estimates of the yield loss from erosion. The estimates
indicated that, if the 1992 erosion rates continued for 100
years, the yield loss at the end of the period would amount to
only ~2-3% (24, 25~.
The extent of soil degradation and loss and its impact on
crop production in developing countries is even less well
understood than in the U.S. The estimates of soil erosion and
degradation for developing countries that appear in the liter-
ature are typically based on expert opinion rather than care-
fully designed and adequately monitored experiments. Lal (27)
indicated 15 years ago that the information needed to assess
the productivity effects of soil erosion in developing countries
were not available for major soils and crops. As far as I have
been able to determine, information on the effects of soil loss
and degradation is still lacking (28~. Studies conducted by
Peter Lindert (29-31 ~ in China and Indonesia provide the only
long term evidence I have been able to identify on the impact
of soil loss in developing countries. These studies indicate,
somewhat surprisingly, that, while there has been some decline
in soil organic matter and nitrogen, there has been little or no
loss of topsoil or in productive capacity over the more than
half-century covered by his study (29-31~. A careful review of
the international literature by Crosson suggests that yield
losses at the global level might be roughly double the rates
estimated for the U.S. (24~.
The fact that the data is so limited should not be taken to
suggest that soil erosion is not a serious problem. But it should
induce some caution in accepting some of the more dramatic
pronouncements about the inability of to sustain agricultural
production (32~. The impact of human-induced soil degrada-
tion and loss is not evenly distributed across agroclimatic
regions, either in developed or developing countries. What I do
feel comfortable in concluding is that the impacts on the
resource base and on regional economies from soil erosion and
degradation are local rather than global. It is unlikely that soil
degradation and erosion will emerge as important threats to
the world food supply in the foreseeable future. Where soil
erosion does represent a significant threat to the resource and
the economic base of an area, the gains from implementation
of the technical and institutional changes necessary to reclaim
degraded soil resources, or at least to prevent further degra-
dation, can be quite substantial.
Water. During the last half-century, many countries have
been undergoing a transition in which water is becoming a
resource of high and increasing value. In the arid and semiarid
areas of the world, water scarcity is becoming an increasingly
serious constraint of growth of agricultural production.h The
change in the economic value of water is the result of the very
large increases in withdrawal of water for domestic and
industrial purposes and, most importantly, for irrigation. The
International Water Management Institute lists 16 countries,
with a total population of 361 million, located primarily in the
Middle East and North Africa, that were experiencing absolute
water scarcity in 1990. The Institute projected that, by 2025, an
hFor a useful review, see Seckler, Molden, and Barker (33~. See also
the Food and Agriculture Organization 4334) and Raskin et al. (35~.
The study by Raskin et al. gives more explicit attention to withdrawals
for domestic, industrial, and environmental purposes. In arid regions
in both developing and developed countries, use of water to protect
instream environmental values is increasingly competitive with with-
drawals for irrigation.
Proc. Natl. Acad. Sci. USA 96 (1999J 5963
additional 23 countries, primarily located in Africa, with a 1990
population of 345 million, plus Northern China and Western
India, where another 360 million people live, will experience
either absolute or severe water scarcity.) The International
Water Management Institute projects a decline in withdrawals
of water for irrigation in almost all of these areas between 1990
and 2025.
During the last half-century, irrigated area in developing
countries more than doubled, from <100 million to almost 200
million hectares. About half of developing country cereal
production is grown on irrigated land (36~. The issue of the
relationship between water scarcity and food production has
generated a substantial debate. It has been suggested that
impending water shortages in North China will be so severe by
2025 that China will need to import between 210 and 370
million metric tons of grain per year to meet the demand
arising out of population and income growth (37~. The Inter-
national Water Management Institute studies indicate that
North China will experience absolute water scarcity while
South China will have surplus water.
Much of public sector irrigation investment has been de-
voted to the development (and rehabilitation) of gravity
irrigation systems. In most arid regions, the topography that is
best suited to the development of large-scale irrigation systems
has already been exploited. Investment costs of adding surface
irrigation capacity have risen by several multiples during the
last half-century. It is unlikely that there will be substantial new
investment in large-scale, gravity-fed irrigation systems in the
foreseeable future unless there is a substantial long-term rise
in food prices.
In spite of the large public investment in gravity irrigation
systems, the area irrigated by using tube wells to pump
groundwater has expanded even more rapidly. In many re-
spects, pump irrigation from aquifers is an ideal form of
irrigation. The water is stored underground with no loss from
evaporation. Water is generally available during the dry season
even during drought years, when reservoirs for surface irriga-
tion may be dry. Access to water is under the control of
individual producers rather than of an often inefficient and
corrupt irrigation bureaucracy.
There are substantial spillover effects or externalities in both
surface and ground water systems that impact directly on
agricultural production. One of the most common problems of
surface water systems is water logging and salinity resulting
from excessive water use and poorly designed drainage sys-
tems. In the Aral Sea Basin in Central Asia, the effects of
excessive water withdrawal for cotton and rice production,
combined with inadequate drainage facilities, has resulted in
water logging and salinity in irrigated areas and contraction of
the Aral Sea, which threatens the economic viability of the
region.3 Another common externality results from extraction of
water from aquifers in excess of recharge, resulting in lowering
Countries characterized by absolute water scarcity do not have
sufficient water resources to maintain 1990 levels of per capita food
production from irrigated agriculture, even at high levels of irrigation
efficiency, and also meet reasonable water needs for domestic,
industrial, and environmental purposes by 2025. Countries character-
ized by severe water scarcity are in regions in which the potential water
resources are sufficient to meet reasonable water needs by 2025, but
only if they make very substantial improvements in water efficiency
and investments in water development. The International Water
Management Institute study assumes that, when withdrawal exceeds
50~o of annual water resource flows, the costs of further water
resource development are likely to be prohibitive (33).
One of the most comprehensive efforts to identify the world's most
threatened regions was organized by a group of scholars from the
Department of Geography at Clark University (38~. For the Aral basin
study see Glazovsky (39~. Although the Aral Sea Basin was the most
severely affected of the nine studied, two other regions were charac-
terized as "endangered," and the patterns of resource exploitation in
the other six were judged to be not sustainable.
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Representative terms from entire chapter:
soil erosion
5964 Colloquium Paper: Ruttan
of the groundwater level and rising pumping costs. In some
countries, these spillover effects are sufficient to offset the
contribution of expansion of irrigated area to agricultural
production.
The institutional arrangements under which producers ob-
tain access to water contribute to inefficient water use. They
are not only an important source of negative spillover effects
but also have failed to induce the development and adoption
of technology that would lead to growth of water productivity
comparable to the increases that have occurred in output per
hectare or output per worker in agriculture. The design of
effective institutional arrangements to induce improvements in
water efficiency and productivity will not be easy. The reforms
that are typically suggested include elimination of subsidies,
design of "constructed markets" to allocate surface water
more efficiently, and a system of quotas, charges, and taxes to
reduce ground water withdrawals to a sustainable level (40,
41~. It is possible to identify some successes from such efforts,
but, in general, it has been difficult to design reforms that are
both economically and politically viable. Transaction costs in
constructed markets are often high. Water use typically in-
volves a wide variety of public values that involve third parties.
It seems clear, however, that the rising economic value of water
and the constraints on water withdrawals that can be antici-
pated can be expected to induce more intensive institutional
reform efforts.
Pest Control. Pest control has become an increasingly
serious constraint on agricultural production in spite of dra-
matic advances in pest control technology over the last half-
century. The major pests of crops and animals include insects,
pathogens, and weeds. Strategies include cultural control,
biological control, pest resistant crop varieties, and chemical
control (42-44~.
Before the latter decades of the 19th century, farmers relied
almost exclusively on cultural methods such as crop rotation in
their efforts to control pests. Chemical controls began in the
1870s with the development of arsenical and copper-based
insecticides. Use of biological control dates from the late 1880s
with the introduction of the vedelia beetle (from Australia) to
control a California citrus pest, the cottony cushion scale.
Efforts also were made to identify, develop, and introduce
pest-resistant crop varieties and animal breeds.
Pest control strategies changed dramatically as a result of the
development of dichlorodiphenyl-trichlorethane (DDT) in the
late 1930s and its use, during World War II, to protect
American troops against typhus. Early tests found DDT to be
effective against almost all insect species and relatively harm-
less to humans, animals, and plants. It was effective at low
application levels and was relatively inexpensive. The effect
was to direct the research efforts of economic entomologists,
and the attention of funding agencies, away from fundamental
research on insect biology, physiology, and ecology, as well as
from the development of alternative methods of insect pest
control. Chemical companies rapidly expanded their research
on synthetic organic insecticides as well as chemical ap-
proaches to the control of pathogens and weeds.
Problems of negative externalities were encountered shortly
after the introduction of DDT. When DDT was introduced in
California to control the cottony cushion scale, its introduced
predator, the vedelia beetle, turned out to be more susceptible
to DDT than the scale. In 1947, just 1 year after its introduc-
tion, citrus growers, confronted with a resurgence of the scale
population, were forced to restrict the use of DDT. In Peru, the
cotton boll worm quickly built up resistance to DDT and other
chlorinated hydrocarbon pesticides. Producers then turned to
the more recently developed, and much more toxic, organo-
phosphate insecticides, which again selected for resistant
strains of the boll worm. In the meanwhile, natural predators
were almost completely exterminated. Cotton production col-
lapsed and was revived only after a program to regulate
Proc. Natl. Acad. Sci. USA 96 (1999)
insecticide use was implemented (43~. Concerns about the
externality effects of the new pesticides emerged first in the
U.S. and other developed countries. The adoption of the high
yielding "green revolution" cereal varieties in developing
countries was associated with a dramatic increase in pesticide
use. When yields were low, there was little benefit from pest
control. As yields rose, the economic incentive to adopt
chemical pest control technologies also rose.
During the l950s, an increasing body of evidence suggested
that the benefits of the pesticides introduced in the 1940s and
early l950s were obtained at a substantial cost. The costs
included not only the increase in resistance to pest control
chemicals in target populations and the destruction of bene-
ficial insects, but also the direct and indirect effects on wildlife
populations and on human health. In the early 1960s, public
concern about these effects was galvanized by Rachel Carson's
dramatic revelations of the effects of the new insecticides (45~.
During the 1960s and early 1970s, the view emerged to the
effect that a coalition of chemical manufacturers, agricultural
interests, and economic entomologists at public universities
were engaged in a "pesticide conspiracy" to block the technical
and institutional changes necessary to achieve a more eco-
nomically viable and ecological benign pest control strategy
(46, 474.
The solution to the pesticide crisis offered by the entomol-
ogy community was Integrated Pest Management (IPM). IPM
involved the integrated use of some or all of the pest control
strategies referred to above. It is more complex for the
producer to implement than spraying by the calendar. It
requires skill in pest monitoring and understanding of insect
ecolo~v. And it often involves cooperation among producers
for effective implementation.k At the time IPM began to be
promoted as a pest control strategy in the 1960s, there was very
little IPM technology available to be transferred to farmers.
IPM represented little more than a rhetorical device to paper
over the differences between economic and ecological ento-
mologists. By the 1970s, sufficient research had been con-
ducted to provide the knowledge to successfully implement a
number of important IPM programs (48~. However, exagger-
ated expectations about the possibility that dramatic reduc-
tions in pesticide use could be achieved without significant
decline in crop yields as a result of adoption of IPM have not
been realized (49-51~.
Integrated approaches to weed management evolved later
than for insect pests, in part because emergence of resistance
to chemical herbicides occurred much more slowly than
resistance by insect pests to insecticides. By the mid-199Os,
however, the development of genetically engineered herbi-
cide-resistant crop varieties resulted in a new set of concerns.
In some cases, herbicide-resistant crops may have beneficial
effects on the environment when, for example, a single
broad spectrum herbicide that breaks down rapidly in the
environment is substituted for several applications of pre-
and postemergence herbicides, or for a herbicide that is more
persistent in the environment. When a single herbicide is
used repeatedly, however, it does pose the danger of select-
ing for herbicide resistant weeds. The impact of agricultural
intensification and the convolution of pathogens, insect
kThe elements of the very successful program to control cotton pests
(boll weevil, pink bollworm, and tobacco budworm) on the high plains
of Texas included (i) establishment of a uniform planting period and
adoption of short duration varieties; (ii) irrigation before planting;
(iii) application of insecticide only in areas in which high bollworm
populations are expected; (iv) selective application of an organophos-
phate insecticide during harvest; (v) defoliation of mature crops (so
all bolls open at the same time); (vi) use of mechanical strippers (to
kill larvae) in harvesting; (vii) shredding of stalks and plow down
immediately after harvest; and (
Colloquium Paper: Ruttan
pests, and weeds will continue to represent a major factor in
directing the allocation of agricultural research efforts to
maintenance research (12~.
Climate Change. In the late 1950s, measurements taken in
Hawaii indicated that carbon dioxide (CO2) was increasing in
the atmosphere. Beginning in the late 1960s, computer model
simulations indicated possible changes in temperature and
precipitation that could occur due to human-induced emission
of CO2 and other "greenhouse gases" into the atmosphere. By
the early 1980s, a fairly broad consensus had emerged in the
climate change research community that energy production
from fossil fuels could, by 2050, result in a doubling of the
atmospheric concentration of CO2, a rise in global average
temperature by 1.5-4.5°C (~2.7-8.0°F), and a complex pattern
of world wide climate changes. Since the beginning of the
1980s, a succession of studies have attempted to assess how an
increase in the atmospheric concentration of CO2 could affect
agricultural production (52-54~.
There are three ways in which increases in CO2 concentra-
tions in the atmosphere may effect agricultural production.
One is that increased CO2 concentration in the atmosphere
may have a positive effect on the growth rates of crop plants
(and weeds) through the CO2 "fertilization effect" and by
decreasing the rate of transpiration. The magnitude of the CO2
fertilization effects remain highly uncertain. Extrapolations
are limited to model-based estimates that use data from
greenhouse or small-scale field experiments. And it has not yet
been possible to separate the effects of the increase in CO2
concentrations over the last half-century from other factors
that have contributed to higher yields. A second way that
agricultural production could be impacted is that higher
temperatures could result in a rise in the sea level, resulting in
inundation of coastal areas and the intrusion of salt water into
ground water aquifers and surface waters. Low lying coastal
agricultural areas in Bangladesh, for example, could be im-
pacted very severely.
The largest impacts on agricultural production will be due to
the effects of CO2-induced changes in temperature, rainfall,
and sunlight. These effects can be expected to vary greatly
across agroclimatic regions. However, greenhouse-induced
warming is expected to be greatest in high midlatitude regions
(>45°) and high latitudes (>60°~. Subtropical and tropical
regions will experience less extreme temperature changes.
Monsoon rains are likely to penetrate further northward.
Northern areas in which production is presently constrained by
length of the growing season, such as the northern fringes of
the Canadian prairie provinces, could expect both higher yields
and an expansion of area devoted to cereals and forage plants.
There has been a substantial change in estimates of the
impact of global climate change on crop yield and agricultural
production. Estimates made in the late 1980s and early 1990s
generally projected rather substantial negative impacts at the
global level (534. More recent studies have tended to project
impacts ranging from slightly negative to slightly positive (55,
56~. These more positive estimates have been due primarily to
two changes in the modeling of climate change. One has been
the incorporation of assumptions about the positive effects of
CO2 fertilization. As noted above, these assumptions remain
controversial because they involve extrapolation from green-
house or very small scale field experiments. The second change
has been due to replacing the static production function or
"dumb farmer" approach employed in earlier models with
estimates of farmers' rational responses to climate change,
including changing in cropping systems and adoption of tech-
nology. As a caveat, several of the models suggest that, while
modest changes in global average surface temperature in the
2.5° range, for example, could have a net positive effect, larger
Proc. Natl. Acad. Sci. USA 96 (1999J 5965
increases, in the 5° range, could have a negative effect on
agricultural production.
The modeling efforts continue, however to employ a "dumb
scientist" assumption. The behavior of public and private
sector suppliers of knowledge and technology has not yet been
incorporated in the models and estimates. Efforts to incorpo-
rate endogenous or induced technical change into climate
change models have been limited by the tractability of the
models (or the modelers). The only successful empirical effort
I am aware of is a study by Evenson and Alves in Brazil (57~.
The Evenson-Alves model incorporates not only the choice of
technology by farmers in response to climate change but also
responses by the public and private suppliers of technology.
The study indicates that, in Brazil, the effect of climate change
alone would be to depress production in the North, Northeast,
and Center-West. In contrast, many areas in the Center-East,
the South, and the Coastal regions would benefit. When the
technical change induced by the climate change is taken into
account, it is expected to compensate for the effect of climate
change in the more disadvantaged regions while the more
favored regions will benefit from both the climate change and
technical change.
None of the models gives adequate attention to the indirect
or interactive effects of climate change. The limited assess-
ments that have been made suggest that, as environmental
stress intensifies as a result of warmer (and, in some areas,
more humid) climates, crops will become more vulnerable to
weeds, insects, and plant diseases (54~. The incidence and
severity of soil erosion, changes in rainfall, surface water
storage, groundwater recharge, the incidence of pests and
pathogens, or frequencies of extreme events, such as drought
or floods, or climate variability have not been incorporated
effectively into the climatic change models. It is possible that
actions taken to mitigate global climate change, such as
land-intensive approaches to carbon sequestering, substitution
of fuels based on agricultural raw materials for petroleum
based fuels, and efforts to control carbon, nitrous oxide, and
methane emissions, could have a larger negative effect of crop
and animal production than the direct impacts of climate
change.
I have not, in this paper, discussed the potential impacts of
health constraints on agricultural production. Improvements
in nutrition associated with growth in agricultural production
has, in many developing countries, contributed to lower infant
mortality and increased life expectancy. But the increase in use
of insecticides and herbicides associated with agricultural
intensification has also had negative effects on the health of
agricultural workers. There are also important health effects,
in both urban and rural areas, of the intensification of indus-
trial production associated with atmospheric, water, and soil
pollution. There are also the health effects associated with the
emergence of new diseases such as AIDS and the emergence
of drug resistance by older parasitic and infectious diseases. It
is not too difficult to visualize situations in particular villages
in which the coincidence of several of these health factors
could result in serious threats to agricultural production. It is
more difficult, but not completely impossible, to visualize
health threats becoming a serious constraint on national
agricultural production (60-62~.
PERSPECTIVE
What inferences do I draw from this review of resource and
environmental constraints on the transition to agricultural
'The Mendelson, Nordhaus, and Shaw model (55) has also been
criticized for underestimating the impact of global climate change on
agriculture in irrigated areas by giving inadequate attention to the way
water is currently used due to distortions associated with water
allocation and pricing (58~.
5966 Colloquium Paper: Ruttan
sustainability? There will, even beyond the middle of the 21st
century, continue to be great diversity among countries and
regions in the transition to agricultural sustainability. It seems
unlikely that the conditions projected in the Barbarization
Scenario will be completely eliminated or that the conditions
projected in the New Sustainability Scenario will be more than
partially realized (Fig. 14.
It is unlikely that soil loss and degradation will represent a
serious constraint on global agricultural production over the
next half-century. But soil loss or degradation could become a
serious constraint on production on a local or regional scale in
some fragile resource areas. This possibility will be greatest if
slow productivity growth in robust resource areas should lead
to intensification or expansion of crop and animal production
in fragile resource areas, i.e., tropical rain forests, arid and
semiarid regions, and the high mountain areas. In some such
areas, however, the possibility of sustainable production can be
enhanced by irrigation, terracing, careful soil management,
and changes in commodity mix and farming systems.
It is also unlikely that lack of water resources will become a
severe constraint on global agricultural production in the
foreseeable future. But in 50-60 of the world's most arid
countries, plus major regions in several other countries, com-
petition from household, industrial, and environmental de-
mands will result in a reallocation of water away from irriga-
tion. In many of these countries, increases in water use
efficiency and changes in farming systems will permit contin-
ued increases in agricultural production. But it seems reason-
able to expect that, in a number of countries, the reduction in
irrigated area will be large enough to result in significant
reductions in agricultural production. Since these countries are
among the world's poorest, some may have great difficulty in
meeting food security needs from either domestic production
or food imports.
The problem of pest and pathogen control may have more
serious implications for sustainable growth in agricultural
production at a global level than either land or water con-
straints. Both the development of resistant crop varieties and
chemical methods of control tend to induce target pest or
pathogen resistance. In addition, international travel and trade
will result in rapid diffusion of traditional and newly emerging
pests and pathogens to favorable environments. As a result,
new pest control technologies must constantly be replaced by
a succession of resistant varieties and chemical (or biochem-
ical) agents. As a result, an increasing share of a constant
research budget will need to be devoted to maintenance
research the research required to sustain existing productiv-
ity levels.
Recent projections of the impact of climate change on global
agricultural production are much more optimistic than pro-
jections made a decade ago. The scientific and empirical basis
for the more optimistic projections is, however, much too
fragile to serve as a secure foundation for policy. There is great
uncertainty about the rate of climate change that can be
expected over the next half-century. All of the projections
employ assumptions that are only weakly grounded in expe-
rience. None of the models gives adequate attention to the
synergistic interactions among climate change, soil loss and
degradation, ground and surface water storage, and the inci-
dence of pests and pathogens. These interactive effects could
add up to a significantly larger burden on sustainable growth
in production than the relatively small effects of each con-
straint considered separately.
A point made repeatedly in this paper is that, while the
constraints discussed do not represent a threat to global food
security, they may, individually or collectively, become a threat
to growth of agricultural production at the regional and local
level in a number of the world's poorest countries. This means
that the transition to agricultural sustainability will, given the
uncertain future, depend on the maintenance and enhance
Proc. Natl. Acad. Sci. USA 96 (1999)
ment of capacity for technical and institutional innovation. A
primary defense against the uncertainty about resource and
environmental constraints is agricultural research capacity.
Research capacity represents the "reserve army" to deal with
uncertainty. The erosion of capacity of the international
agricultural research system will have to be reversed; capacity
in the presently developed countries will have to be at least
maintained; and capacity in the larger developing countries
will have to substantially strengthened. Smaller countries will
need, at the very least, to strengthen their capacity to borrow,
adapt, and diffuse technology from countries in comparable
agroclimatic regions. It also means that more secure bridges
must be built between the "island empires" of agriculture,
environment, and health.
If the world fails to meet the challenge of a transition to
sustainable growth in agricultural production, the failure will
be at least as much in the area of institutional innovation as in
the area of resource and environmental constraints. This is not
an optimistic conclusion. The design of institutions capable of
achieving compatibility between individual, organizational,
and social objectives remains an art rather than a science, The
incentive compatibility problem has not been solved analyti-
cally, even at the most abstract theoretical level (63, 64~. At our
present stage of knowledge, institutional design is analogous to
driving down a four-lane highway looking out of the rear view
mirror. We are better at making course corrections when we
start to run off the highway than at using foresight to navigate
the transition to sustainability.
The author is indebted to Randolph Barker, Pierre Crosson, and
Gretchen Daily and to the participants in the University of Minnesota
Agricultural Development Workshop for comments on an earlier draft
of this paper.
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