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OCR for page 78
7
Food, Water, and
Changing Climate
As scientists work to improve their predictions of change
in the earth's climate, a long-stancling question assumes ever-
greater currency: How many people can the planet support
without using up our natural resources and forever undermin-
ing the earth's ability to support people in the future? In other
worcls, what is the carrying capacity of the earth?
Today, assuming equitable distribution to the 5 billion peo-
ple all over the world, the earth certainly provides enough food
for an adequate diet. This fact, however, conceals a distressing
paradox: In recent years, although the earth produced record
amounts of grains, half a billion people were seriously mal-
nourished. One reason is the unrelenting poverty that prevents
millions from purchasing adequate food even when it is avail-
able. Another reason is that in many cases starvation reflects not
the absence of food but rather poor distribution due to politics
or civil war, as in Sudan and Ethiopia during the 1980s. Societal
excuses notwithstanding, in some parts of the world, the ability
to provide food increasingly fails to keep pace with population
growth. In sub-Saharan Africa, for example, the rate of popula-
tion growth is 40 percent faster than the rate of growth in food
production.
78
OCR for page 79
FOOD, WATER, AND CHANGING CLIMATE
79
Scientists, economists, and philosophers have been fasci-
nated by the notion of carrying capacity since Thomas Malthus
suggested in 1812 that rates of increases in food production
lagged so far behind population growth that starvation was in-
evitable. After years of study and debate, the definition and
applications of this concept are still evolving. Malthus thought
that ultimately a shortage of food would be the limiting fac-
tor on population growth, but his predictions ctid not take into
account the remarkable advances in our ability to produce food.
THE GLOBAL HARVEST
Taking the world as a whole, Lester Brown, in the WorId-
watch Institute's annual State of the World assessments, reports
that grain production per person has climbed an impressive 40
percent between 1950 and 1984. The "green revolution" of the
1960s-which introduced new varieties of rice and wheat and
intensified use of pesticides, fertilizer, and irrigation is respon-
sible for a major share of this increase. But from 1984 through
198S, grain production per person fell. While per capita grain
production rebounded in 1989, it was still below 1984 levels.
Such fluctuations do not suggest long-term trends or imply that
environmental deterioration, rather than economic forces or iso-
latecl years of adverse weather, is solely responsible. They do
illustrate that the earth's ability to supply food to the growing
population cannot be taken for granted.
Discussions of how many people the planet can support
often begin with some widely accepted numbers. Sometime in
1987, for instance, the worId's population crossed the 5-billion
mark. Demographers project that by the end of the coming
century our numbers will increase to 10 billion or more before
they begin to stabilize, with more than 95 percent of the growth
occurring in the developing world.
Paul Ehrlich, Gretchen Daily, Anne Ehrlich, and Peter Vi-
tousek, all at Stanford University, and Pamela Matson, at NASA
Ames Research Center, are part of the Stanford Carrying Ca-
pacity Group. They attribute carrying capacity not only to
OCR for page 80
80
tudes as we!
THE FACES OF GLOBAL ENVIRONMENTAL CHANGE
the earth's physical and biological capabilities to provide re-
sources necessary for food, clothing, and other essentials, but
to humanity's ability to develop new technologies and atti
1. Through cultural evolution, they explain, hu-
man beings may quickly shift their demand for and ability
to extract different resources. At the same time, natural and
human-induced changes with global environmental change as
a primary example alter the distribution and abundance of
~ ~ ,
. ~ ~ ~ ~ ~ ~ ~ · 1 _ ~ ~ ~ ~ 1 ~
available resources. coon araws parncu~ar ar~ennon Because ~
production is sensitive to changes in the environment, particu-
larly to changes in temperature and precipitation, and yet basic
human nutritional requirements are relatively inflexible.
The ability of the earth to produce food depends heavily
on elements of what can be considered our species' capital:
groundwater, the genetic diversity of nonhuman species, and
productive soil. These natural assets, which population ecolo-
gist Ehrlich describes as part of "humanity's one-time inheri-
tance," once seemed limitless. Now, he explains, groundwater
in many places is being pumped faster than it is being recharged.
Untold species and millions of genetically distinct populations
that potentially provide the genetic resources for new crops dis-
appear each year as tropical forests are cleared. Fertile soil,
which is generated at rates on the order of inches per millen-
nium, is losing its productivity in many parts of the world
because of erosion or salinization, a process in which salts re-
main as irrigation water evaporates from the soil surface. Such
direct human impact on carrying capacity is especially evident
on marginal land in arid and semiarid regions Darticularlv in
Africa.
-A-- -, ~
A 1988 study by Robert Chen and colleagues for the Alan
Shawn Feinste~n World Hunger Program at Brown University
estimated that even if food were equitably distributed (with
nothing diverted to livestock), the amount of food produced On
1985 an all-time record-could have provided a minimal veg-
etarian diet to about 6 billion people, a number we will exceed
by the end of the century. The same global harvest, allowing a
diet with about 15 percent of the calories from animal products,
OCR for page 81
FOOD, WATER, AND CHANGING CLIMATE
400-
300
Oh
o 200
y
100 ~
O l l
1950 1960 1970
81
,~
~4
1 1 1
1980 1990 2000
YEAR
World grain production per capita, 195~1988. (Reprinted, by permission, from State
of the World 1989. Copyright (I) 1989, by Worldwatch Institute, all rights reserved.)
could feed some 4 billion people. A diet consisting of 35 per-
cent animal products, similar to that consumed by most North
Americans and West Europeans today, could be provided to only
about 2.5 billion people less than half of today's population.
These estimates assume that 40 percent of the food harvested
will not be available to human use because of wastage and con-
sumption by pests. But as many economists have pointer! out,
if the poorest people had more wealth, the increased demand
might well stimulate production of more food. So the issue of
whether there would be enough food is never quite resolved.
Based on current projections for population growth and
increases in per capita income, world demand for food in the
middle of the next century couIct easily be 2 to 2.5 times the level
of the mid-19SOs, according to calculations by William Easterling
Ill and Pierre Crosson, both of Resources for the Future, and
Martin Parry, of the Atmospheric Impact Research Group at
the University of Birmingham in the United Kingdom. Crosson
and his colleague Norman Rosenberg, also at Resources for the
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82
THE FACES OF GLOBAL ENVIRONMENTAL CHANGE
Future, believe there is room for optimism. They predict that if
food production grows at or even slower than the current rate,
there would still be enough food for the 10 billion people by the
time they arrive. They temper this conclusion with the caveat
that the ability to produce enough food can be sustained only
if techniques that are less environmentally damaging than the
current monoculture crops and heavy applications of chemical
fertilizers and pesticides are developed and used.
The expansion of food production to feed the worId's grow-
ing population is not likely to be accomplished by increasing the
worId's cultivated area. Even though only half of the potentially
arable land is being farmed, expansion onto new land is lim-
ited because remaining land may be geographically inaccessible
(uncultivated land is most scarce in many developing coun-
tries where population is growing fastest), infested by pests that
transmit parasitic diseases such as trypanosomiasis (sleeping
sickness), or covered by soils so thin or acidic that agriculture
cannot be sustained. In fact, the land area planted in grain
worldwide has actually declined by about 7 percent since 1981,
owing mainly to abandonment of cleteriorated land, conversion
of cropland to nonfarm uses, especially in clensely populated re-
gions, and "set-asides" in the United States (a practice in which
farmers are compensated for retiring cropland to limit overpro-
duction). The primary prospects for expanding food production
are the potential for increasing yields on existing agricultural
land through more intensive cropping, increased fertilizer use,
and the development of more productive strains, and increased
reliance on anct clevelopment of new methods for harvesting
food from the oceans.
THE EFFECT OF GLOBAL WARMING ON
FOOD PRODUCTION
Whether the projected global warming will be good or bad
for agriculture depends on the specific location and on how
much warming occurs. Little is certain as scientists try to sort
OCR for page 83
FOOD, WATER, AND CHANGING CLIMATE
83
out complexities such as how changes in temperature and pre-
cipitation patterns may affect agricultural productivity and also
how crop yielcl may change as plants respond to increased con-
centrations of carbon dioxide, which can stimulate growth and
reduce water consumption. Crop yields are certain to decline
in some regions and increase in others. But researchers, lacking
knowledge about the regional distribution of climate changes,
can only estimate where and by how much these shifts in pro-
ductivity will occur.
Scientists trying to simulate potential effects of global warm-
ing on agriculture rely on the same general circulation climate
models (GCMs) that other scientists use to study global pro-
cesses (see chapter 61. For the purposes of the agricultural mod-
els, the GCMs project some important changes in climate. In
particular they find that warming will be greatest in the high
latitudes, that soils may tend to be ctrier in mid-continental re-
gions in summer, and that globally the hydrologic cycle will
intensify more rain, more evaporation as the earth's sur-
face warms. The models show that with an effective doubling
of preindustrial carbon dioxide concentrations (that is, with a
combination of all trace greenhouse gases that equals the heat-
trapping effect of a doubling of the concentration of carbon
dioxide), evaporation on a global basis will increase by 7 to 12
percent. The atmosphere cannot store large amounts of water
vapor, anct so precipitation will increase. The increases will not
be uniformly distributed, however; nor will the proportions of
rain, snow, or dew necessarily remain the same.
In a summary of the causes, impacts, and uncertainties as-
sociated with the greenhouse effect, Stephen H. Schneider, of
the National Center for Atmospheric Research in Boulder, Col-
orado, and Rosenberg suggest that if analyses of the effects of
temperature changes on evaporation and runoff of water from
the land surface are correct, "the greatest impact of greenhouse
warming on natural resources will occur because of changes in
the seasonality and amounts of precipitation and of evapotran-
spiration."
Parry, with colleagues Timothy Carter, also of the University
OCR for page 84
84
THE FACES OF GLOBAL ENVIRONMENTAL CHANGE
of Birmingham, and Nicolaas Konijn, of Agricultural University
in the Netherlands, synthesized results of a multinational study
of the impacts of climatic variations on agriculture. The study,
sponsored by the International Institute for Applied Systems
Analysis and the U.N. Environment Programme, used the God-
dard Institute for Space Science (GISS) climate mode} to study
the effects on crop yielcis of warming due to an effective dou-
bling of carbon dioxide.
in the study, Parry and colleagues compared average yields
expected under current climate conditions in several Northern
Hemisphere regions with average yields that might be expected
with effective doubling of carbon dioxide warming. For sim-
plicity, they assumed the same technology and management
used today, which they acknowledge is not a realistic assump-
tion. They did not consider the fertilizing and moisture-saving
effects of added carbon dioxicle on the plants.
Parry, Carter, and Konijn report that if summer dryness
becomes more frequent in mid-latitudes as predicted for the
Northern Hemisphere, decreases in yields might occur in the
productive areas of North America anct the USSR. In general,
they suggest, the higher temperatures would favor higher yields
of cereal cror)s now Frown in regions where current tempera-
lures limit the growing season. For climate conditions produced
by effective carbon dioxide doubling as projected by the GISS
model, for instance, wheat yields increase by about one third in
the central European region of the Soviet Union, where there is
currently a short, coo! growing season. The yields of barley, on
the other hand, which thrives under coo! temperate conditions,
drop by about 4 percent. Where cereal production is already
prone to drought, increased evaporation rates predicted by the
climate mode! could limit any increase in yields that would be
expected due to higher temperatures. This could be the case in
Saskatchewan, for instance, where increases in yields of spring-
sown wheat plants could be lessened by one fifth to one third.
The direct effects of carbon dioxide on plant growth and use
of water complicate efforts to predict how future climate change
induced by rising concentrations of greenhouse gases may affect
r- - ~
OCR for page 85
FOOD, WATER, AND CHANGING CLIMATE
85
agriculture, forests, and other ecosystems. As carbon dioxide
concentrations increase, rates of photosynthesis increase in most
plants. At the same time, with rising concentrations of carbon
dioxide plants partially close their stomates, the pores through
which water vapor and carbon dioxide pass. Because plants
use less water (transpiration) per unit leaf area when exposed
to elevated levels of carbon dioxide, water use efficiency may
increase. So far, effects of carbon dioxide enrichment have been
studied primarily under controlled experimental conditions. If
the positive direct effects occur in the field, the combinations of
increased growth and improved water use efficiency may help
offset the negative effects of climate change on crops.
WATER SUPPLY, IRRIGATION, AND
THE HYDROLOGIC CYCLE
One of the more generally accepted conclusions of the gen-
eral circulation climate models is that as average global tem-
peratures increase, the hydrologic cycle will speed up, increas-
ing global precipitation. This does not mean, however, that
the added precipitation will fall where or when it is needed.
As temperature and precipitation patterns change, so will soil
moisture and the timing and magnitude of runoff, with possibly
adverse effects for many of the world's important agricultural
areas. One likely consequence of these changes would be that
demand for water, especially for irrigation, would increase in
some regions.
The task of estimating future changes in water supply is
difficult because the resolution of global climate models is too
coarse to represent the complexity of regional or local changes.
Many water problems such as floods and drought occur on these
spatial scales. Despite their imperfections, however, the models
tend to agree on several key points.
One point on which models tend to be in agreement in-
volves changes in soil wetness, which may be just as impor-
tant as changes in atmospheric temperature. The soil moisture
regime determines the types and extent of vegetation that can
OCR for page 86
86
THE FACES OF GLOBAL ENVIRONMENTAL CHANGE
thrive in a given location. Some studies, such as the ones con-
ducted by Syukuro Manabe and Richard Wetherald, both of the
NOAA Geophysical Fluid Dynamics Laboratory in Princeton,
New Jersey, predict that as the concentrations of greenhouse
gases increase, soil will become dryer in summer over vast ex-
panses of the middle and high latitudes including the U.S.
Great Plains, Westem Europe, northern Canada, and Siberia.
Mode! results suggest that there would be significant chang-
es in runoff patterns under a changing climate. Runoff is sen-
sitive to changes in precipitation and to evaporation, which is
strongly affected by temperature. In many regions of the world,
runoff comes as snow melts. With higher temperatures, relative
amounts of rain and snow are likely to shift, as will the timing
and speed of snowmelt. Peter H. Gleick, of the Pacific Institute
for Studies in Development, the Environment, and Security in
Berkeley, California, identifies in the 1989 publication Greenhouse
Warming: Abatement and Adaptation a seasonal effect for basins
in the western United States In which changes in runoff patterns
may alter the likelihood of flooding and the availability of water
during such times as the peak irrigation season. Similar changes
are predicted for China, Canada, and Europe.
One implication of such findings is that if global warming
becomes a reality, crop irrigation requirements are certain to
increase, but farmers may find it difficult to expand the area of
irrigated cropland, or even to maintain present irrigation levels.
Agriculture already accounts for three quarters of the fresh water
used globally. A 1989 National Research Council study states
that in the United States, agriculture accounts for 85 percent of
all consumptive uses of water; of this amount, 94 percent is used
for irrigation. But if water supplies diminish, other uses such
as industry, drinking water, and sanitation would also compete
for the available fresh water.
Dean F. Peterson and Andrew Keller, both then at Utah State
University, computed how three levels of climate change 3°C
(5.5°F) warming, 3°C warming with a 10 percent increase in
precipitation, and 3°C warming with a 10 percent decrease in
precipitation-would affect irrigation requirements. In all three
OCR for page 87
FOOD, WATER, AND CHANGING CLIMATE
87
scenarios, irrigation increased because of the longer growing
season, shifts in crops and more multiple cropping (more than
one crop grown in a growing season), and greater potential
evapotranspiration.
Irrigation is the underpinning of the world food production
system. For millennia, farmers have relied on irrigation to in-
crease yields of crops and to free them from the uncertainties
in the timing and amount of rainfall. In some areas, irrigation
makes farming possible; in others, it augments rainfall, with of-
ten dramatic results. In the Unitec! States, only 13 percent of the
cropland is irrigated, but this land accounts for nearly one third
of the value of crops produced. In 1985, the 270 million hectares
(667 million acres) of the worId's irrigated cropland provided
nearly one third of the harvest. These predicted changes in pre-
cipitation and runoff would affect the availability of water for
irrigation and hence food production.
EXPLORING AVENUES FOR ADAPTATION
The history of civilization is punctuated by swings of climate
that have tried the ingenuity of people drawing their livelihood
from the land. Sometimes societies can take steps to moderate
the severe effects of climate swings by changing pricing struc-
tures or providing assistance to farmers.
In other cases, historians believe that climate change, com-
bined with a lack of adaptation on the part of society, has led
to the decline of civilizations. In a joint publication of the U.S.
EPA and the U.N. Environment Programme, Martin Parry cites
accounts of the Norse settlers in Greenland during the period
between 1250 and 1500, the beginning of the Tithe Ice Age.
The Norse settled along the GreenIanct coast around 985. By the
thirteenth century the 6000 Norse inhabitants in two settlements
faced a constellation of stressful circumstances: hostile Inuit, a
declining European market for walrus ivory, and sequences of
coo! summers and stormy winters. The Norse did not opt to ex-
ploit the seas, as the Tnuit did with such success, but continued
to raise livestock despite the reduced capacity of the pastures.
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88
THE FACES OF GLOBAL ENVIRONMENTAL CHANGE
Between 1350 and 1450, the Norse abandoned the settlements,
while the Tnuit continued to survive there.
The experience of the Norse settlers is an extreme example,
Parry explains, of how societies "can fad! to identify and im-
plement appropriate policies of response, not only to climatic
change but to the synergistic effects of a number of concurrent
events." This historical lesson, he suggests, shows the value
of designing policies that respond to the host of difficult en-
vironmental problems facing us today. The effects of climatic
disruption can reverberate throughout an entire society, from the
fortunes of specific farmers and regions, to national and global
food supplies, to trade imbalances and the global economy.
As the initial steps in analyzing the impacts of climate
change on agricultural yields, the studies mentioned above
largely assume that farm policy, management, and technol-
ogy remain as they are today. But these systems are far from
static. it is inconceivable that farmers will not react. Their liveli-
hood is defined by continual adjustment to changing patterns
of weather and consumer demand. Farmers in the Midwestern
United States, for instance, after experiencing the 1988 drought
that reduced corn harvests nationwide by almost 40 percent,
took special care to sow their 1989 spring crops early in case
the drought persisted. Besides adjustments in planting and
harvest dates, other important adaptations at the farm level
include changes in tiliage practices; crop varieties, species, and
rotations; and fertilizer, herbicide, and pesticide applications.
Farmers may also improve existing irrigation efficiency or in-
stall new irrigation facilities. At the regional level, agricultural
market, transportation, finance, and water resources infrastruc-
tures are very likely to change, as are national farm policy and
international trade agreements.
An analysis by Easterling, Parry, and Crosson finds that if
growing seasons in coo! regions become longer and warmer,
farmers could increase yields substantially by substituting va-
rieties used today for varieties that already thrive elsewhere
under higher temperatures. Under conditions of effective car-
bon dioxide doubling, if late-maturing rice now grown in central
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FOOD, WATER, AND CHANGING CLIMATE
89
Japan, for instance, were planted in northern Japan, yields might
increase by 26 percent.
The efficacy and the cost of these adjustments depend in part
on the severity of the climate change experienced. As Cynthia
Rosenzweig, a researcher at Columbia University and NASA's
Goddard Institute for Space Studies, points out in testimony
presented to the U.S. House of Representatives Committee on
Agriculture, "Farmers can make some adjustments to less severe
climate change by planting earlier, substituting better-adapted
crop varieties and species, and Increasing demand for water for
irrigation. More severe climate change will likely require ma-
jor adaptations, including expansion of irrigation infrastructure,
farm abandonment and rural dislocation, In some regions."
A special burden may fall on the half billion poorest and
hungriest farmers of the world. Robert Kates, director of the
Alan Shawn Feinste~n World Hunger Program at Brown Uni-
versity, notes that they are increasingly finding themselves re-
stricted to ecologically marginal land and water resources as
their numbers increase and traditional access to important sea-
sonal uses of land or water are lost to development, dams for
electricity production, large farms for export crops, or even
wildlife and forest conservation. Forced onto marginal land,
they add to its degradation. And they may be the ultimate
victims of global change, having neither the resources to take
advantage of climates more favorable for agriculture nor the
resources to cope with a less productive climate.
Although critical uncertainties exist about the magnitude
and timing of predicted warming and agricultural systems are
sure to adjust in many ways, climate change raises long-term
concerns about agricultural productivity, depletions of major
resources (especially land and water), viability of rural com-
munities, and the environment. The concurrent projections of
population increases and vulnerability of carrying capacity de-
scribed early in this chapter can only add to the already enor-
mous challenges currently facing global agriculture.
Representative terms from entire chapter:
food production
