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Technological Trajectories and the Human Environment. 1997. Pp. 56-73. Washington, DC: National Academy Press. How Much Land Can Ten Billion People Spare for Nature? PAUL E. WAGGONER If people keep multiplying and farmers keep farming as they do now, farm- ers will soon need to grow their crops on twice as large an area as what they use todays Doubling the population without changing the way we farm would ex- pand the cropland from its present tenth of the world's land to about a fifth. More than any other factor, the success farmers have in feeding more people per hect- are (ha) will govern what humanity is able to spare for Nature. I capitalize Nature here and throughout to indicate a specific definition, namely, the features and products of the earth itself, as contrasted with those of human civilization. My essay presumes a population of ten billion people because that seems to be the round number in sight. The billions may level off at ten, or they may grow further (Lutz, 1994; see also Kates, this volume). In either case, we must contem plate ten billion. I presume also that humanity should spare lots of land for Nature. Propo- nents of the sparing of land reason about portfolio, money, and ethics. They argue that sparing land for Nature brings security by assuring a portfolio of biological diversity. They assert that Nature saves our money through her free ecosystem services (Norton, 1988~. At bottom, however, is the ethical argument that sur- vives quibbling over the utility of genes in a jungle or whether a marsh purifies water more cheaply than does a sewage plant. Although most religions empha- size humanity, even Genesis declares, "Let the waters bring forth swarms of living creatures, and let birds fly above the earth.... And God saw that it was good." My title can presume, therefore, that humanity should spare land for Nature without further justification (see Meyer-Abich, this volume). The following example shows that expecting farmers to spare land is not a 56

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HOW MUCH LAND CAN BE SPARED FOR NATURE? 70 in ~ 60 o ~0 o ._ - 40 30 20 10 1965 1970 1975 1980 - 57 I'm/ = Wheat Produced (millions of tons) . ~J - ~17 ~ ~ ~1 . . , 1 1 it' ~ Land Spared 32 44 ~0 57 _ ~_ _ Land Used Year 1 985 1 990 1 995 FIGURE 1 The land Indian farmers spared by raising wheat yields. NOTE: The upper line shows the area Indian farmers would have harvested at 1961-1966 yields to grow what they produced. The lower line shows the area they actually harvested. The farmers spared the difference. The numerals attached to the squares show the millions of tons of wheat produced in six exemplary years. SOURCE: Extends a table compiled by Borlaug (1987). futile wish. From 1961 to 1966, Indian farmers on average grew 0.83 tons of wheat per hectare on 13 million hectares of land. Then, applying the technology of the Green Revolution, they raised production more than fivefold and used only 80 percent more land. Looking back from 1994 to 1961-1966 one can see that Indian farmers spared 44 million ha, about the area of California, by growing more per hectare (see Figure 11. "How much land can ten billion people spare for Nature?" is a farmer's question; asking it is justified, and answering it is not futile. MAKING DO WITH PRESENT FARMING The answer to what farmers can grow rests first on what they do grow today, using 11 percent of the world's land, the 1.4 billion ha of cropland. We can translate all agricultural production into food energy, or calories, and protein. Actual national food supplies range from about 1,800 to 3,900 calories and 40 to 130 grams of protein. The US National Research Council recommends between

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58 PAUL E. WAGGONER 1,900 and 3,000 calories and 50 to 60 grams of protein per day per person (FAO, 1992; National Research Council, 1989~. By dividing today's total calories and protein into rations for ten billion people, we can relate present production to future needs. As evident in Figure 2, food crops, such as wheat and potatoes, would supply about 1,800 calones; feed crops, such as maize and soybeans, would give another 1,000 calories to each of the ten billion people. Other agricultural products such as tobacco and rubber are neither food nor feed but could be replaced by other crops. This replacement of these other present products would provide little in the form of calories and protein for ten billion people. Animals appear twice in our accounting. Animal products, mainly meat and eggs, provide a lot of protein and also add some calories. The calories and protein for draft animals require some explanation: they represent consumption by the animals. In 1910 the horses and mules on Amencan farms and in Amencan cities consumed feed that was grown on an area 44 percent as large as that used to cultivate products for domestic use; their replacement by tractors and trucks has been blamed for the American grain surplus of the 1930s (lIassebrook and Hegyes, 1989; US Department of Agnculture, 1962~. The present global popula- tion of water buffaloes (139 million) and camels (20 million) will surprise a Westerner, as will how much they consume. 1 IS00 C,) 11200 A 1,OOO 800 600 400 200 1,S00 ~ If ~ Calories 1,400 _ _ 1 ~1 ~! ~ ~ ~ o ~0 ~0 o 40 ~ Q ._ to Q 10 Food Feed Other Arlimai Draft Orop Orop Orop Product O FIGURE 2 World agricultural production of calories and protein and the consumption of draft animals. NOTE: The calories or protein in each class are averages per day per person for ten billion people.

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HOW MUCH LAND CAN BE SPARED FOR NATURE? 59 What is the sum of all the categories? If we stopped feeding crops to animals, became vegetarians, and replaced coffee beans with garbanzo beans, the crop- lands would produce 2,900 consumable calories. What should the animal prod- ucts add? Even efficient broiler chickens put only about a fifth of the calories they eat into meat.2 Grazing animals eat more than feed crops, so agriculture, if not cropland, must be credited with some part of the animal calories. Allowing for some further release of calories by reduction in animal numbers but also a con- tinuing role for draft animals, I add 200 calories to the 2,900 calories in crops, bringing the total for ten billion people to 3,100 calories. I simply leave fish on the table without counting its contribution. The sum of 3,100 calories per day for a population of ten billion exceeds the recommended daily allowances, and it exceeds the 2,920 calories that the Japa- nese consume today. The same accounting provides an ample amount of protein for ten billion people. This accounting of present farming makes the idea of sustaining a population of ten billion while sparing land for Nature conceivable. Although today's farming could sustain ten billion people, their wants are surely more than just sustenance. Prophesying wants is chancy. Because animals eat more calories in feed than they give in milk, meat, or eggs, future wants must encompass original calories those for people plus their beasts. Forecasts of consumption of original calories from rising income alone reach as high as 10,000, but caloric restraint can limit the rise to only 4,400 per person per day (Parikh, 1992; Sanderson, 1988~. Will people who are sticking to their accustomed meaty diets spoil this picture of original calories and my implication that the 3,000 calories supplied by today's agriculture might suffice? Large numbers of people do change what they eat, as widespread rises in meat consumption in conjunction with riches in fact illustrate. Nevertheless, annual American beef consumption peaked in 1976 at close to 60 kilograms per person and has since fallen to about 45 kilograms. The success of McDonald's restaurants, interestingly, has been attributed to potatoes rather than to hamburger, and the consumption of potatoes has accordingly crept up. Since 1910, fat in the American diet has increased 50 percent, but its rise encompassed the opposing trends of much more fat from plants and much less from animals (Kroc, 19771.3 In summary, by eating a more or less vegetarian diet we can change dramatically the number of people that a plot of land can feed, and over periods of decades large numbers do change diets. LIMITS TO YIELDS OF FOOD Suppose we do not simplify our diets and restrain our appetites. Might not global shortages of the essentials needed for photosynthesis still fulfill the Malthu- sian fears for ten billion or inhibit their ability to spare land for Nature? At bottom, food comes from photosynthesis, supplied with carbon dioxide (CO2) and water to combine into carbohydrates, energized by sunlight, and

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60 PAUL E. WAGGONER supplemented with fertilizer. Glut has driven fertilizer prices down. Global use has been level since 1988 and in the United States since 1980. Globally, sunlight and, increasingly, CO2 are also abundant. Because the same pores that admit CO2 into leaves let water out, an iron correlation attaches photosynthesis to water. But globally the water on land far exceeds the amount needed to grow food for ten billion people.4 Although cropland per capita expanded from the year 1700 to 1950, it has since shrunk while per capita food production has risen (Richards, 1990; FAO, 1992. Having techniques that raise yield per hectare and having farmers use these techniques are clearly preeminent in this historic reversal. About 1940, World War II ignited the technological fuel that had been accumulating for a generation in industrial nations, and then, under the banner of the Green Revolu- tion of the 1960s, similar techniques raised yields worldwide. The rising trend, illustrated in Figure 3 by wheat yields in three nations, is familiar. But when will an upper limit end the trend? The supplies of sunlight and water seem too large to cap yields until well past ten billion. Setting the limit by fitting curves to the actual data in Figure 3 gives too much latitude to pessimism or optimism. I chose, therefore, the real yield grown currently by a contest winner as a prospective limit. _ _ 0 France U.~. _ s _ ~ 4 _ ct _ 1 2 ~"~''31~;.~6'~=' - ~#~-~ 1 1 1 f) Hi_ 1 800 1 840 1 880 1 920 1 960 2000 Year FIGURE 3 The course of wheat yields in tons/hectare (t/ha) in Ireland, France, and the United States.

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HOW MUCH LAND CAN BE SPARED FOR NATURE? 25 ~0 s 15 =5 a) ~ 1 0 ._ . Pasco, Washington ~ 1992 _ _ / /Logistic rise ~ at 3.6~Jyr / to 20.7 tJha ~ _ ~. my_ 1 _- O 1 1 1 1 1 1940 1960 1980 2000 2020 2040 2060 Year 61 FIGURE 4 The logistic rise of the national average of US maize yields toward a maxi- mum of 21 tons/hectare Steal. Maize, with its efficient photosynthesis, is a productive crop. In 1992 the annual National (US) Corn Growers' Association competition enrolled 2,470 entries from forty-four states (National Corn Growers' Association, 1993, 1994~. To enroll, farmers had to enter a minimum of 4 ha of maize and keep accurate production and harvest records. The winning, irrigated field in Pasco, Washing- ton (46 north with a sunny climate) grew a full 21 tons (t) per hectare! There were other yields above 18 t/ha (287 bushels per acre), proving that 21 t was not a fluke. Providing still further proof that it was no fluke, the Pasco farmer came back in abnormally cool, wet 1993 to grow 19.6 t/ha on his supervised area and 16.3 t on 575 ha. Twenty-one tons would feed eighty people 2,900 calories/day for a year. At eighty people per hectare, 125 million ha, or less than a tenth of the present cropland, could support a population of ten billion. In Figure 4 a logistic curve rises with the actual average American maize yields toward the limit of the winning 1992 yield. Pessimists will worry whether national averages can approach the yield of the irrigated winner. They may rea- son that yields far above the primitive ones mean more effort must go into maintenance of the yields (Plucknett and Smith, 1986), and they may observe that averages have recently fallen and are further below the trend than typically oc- curred during 1940-1970. Optimists will trust that new techniques can raise the limit above 21 t and that a relay team of maintenance research and application will steady the annual averages. But surely all will agree that, since a farmer grew a real yield of 21 t on 4 ha while the national average in an industrial nation lies

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62 PAUL E. WAGGONER near 7 t, scope remains for raising yields to feed people everywhere while sparing land for Nature. BUT IN THE END, WILL FARMERS SPARE LAND FOR NATURE? Production does fluctuate, and people do panic. For example, in the early 1970s fallen production drove food prices up, and US soybean prices doubled. Anxious academics and politicians launched world hunger studies. Then produc- tion recovered, sinking prices and bankrupting farmers. Looking beyond fluctua- tions-and grain prices in 1996 show we are suffering one right now-takes steady nerves. The logistic curve extending past improvements in yields toward 21 t/ha could mislead humanity into thinking that an unseen hand lifts yields effortlessly. In fact, vigorous research and enterprising farmers do the lifting. Remembering the lag of decades between discoveries and their impact on world averages, one asks whether any innovations are on the shelf that can raise yields soon. Heralded for decades, some techniques from biotechnology now sit prominently poised for application, and both scientists and practical people expect them to raise yields as well as protect crops and lessen environmental harm (US Congress, Office of Technology Assessment, 1992; Weiss and Brayman, 1992~. Concrete, statistical evidence that techniques remain to be more fully used appears in the comparison of best and average practices of maize farmers (Iowa Crop Improvement Association, personal communication; see also various years of the FAO Yearbook and the US Department of Agriculture's Agricultural Sta- tistics). Figure 5 displays the trends since 1960 of maize yields grown by the winners of the Iowa Master Corn Growers' Contest and also the trends of average yields by Iowa and world farmers. In percentages, the annual gains by world and Iowa averages do exceed the gain by Iowa Masters. Absolutely, however, the Masters gained 0.14 t/ha annually, more than the Iowa average and twice the gain of the world average. The winners of the Iowa Master Soybean Growers' Contest also steadily stay ahead of the Iowa average soybean yields. The reality of win- ners staying steadily ahead of averages confirms that new technology remains at hand for American farmers. A survey of irrigated Pakistani farms shows a similar gap between master and average yields. Ahmad's tabulation of yields of major crops showed that progressive Pakistanis grow about three times the average yields (Ahmad, 1987~. Technology remains on a nearby shelf for farmers every- where. Because widespread use lags behind discovery by decades, the inventory on the shelf cannot be filled on need but must be replenished continually. The expenditures by the Consultative Group on International Agricultural Research provide an index of effort to refresh the inventory worldwide. Expenditures, which are on the order of a quarter billion dollars, peaked in 1989 and in 1994

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HOW MUCH LAND CAN BE SPARED FOR NATURE? 20 15 ~10 N ._ Ct ~ = 1 _ 1 ~ i ~ , _ _ O 1 1 1960 1965 1970 ,,. ,`~,_-~ I lowa Master \1 lowa Average World Average 63 1975 1980 1985 1990 1995 Year FIGURE 5 The trends since 1960 of maize yields in tons/hectare (t/ha) grown by the winners of the Iowa Master Corn Growers' Contest and also of average yields of Iowa and world farmers. NOTE: The rising trend of per-year yields for Iowa Mas- ters is 1.1 percent, or 0.14 t/ha; for Iowa, the average is 1.S percent, or 0.10 t/ha; and for world maize growers, the average is 2.2 percent, or 0.06 t/ha. were about 20 percent below the peak.5 So while the shelf currently holds tech- nology, what it will hold in a few decades causes us to worry justifiably. Technology left on the shelf butters no parsnips. Whether it will be em- ployed depends on the profit the farmer foresees or the rules that discourage him. In Transforming Traditional Agriculture, Schultz (1964) argues that even poor farmers in poor places do profitable things. A book with the illuminating title of The Bias Against Agriculture (Bautista and Valdes, 1993), however, tells how societies have both discouraged and encouraged farmers' production. For ex- ample, in Peru during 1969-1973 favors for industry and price controls on farm products lowered the production of farm products. In Zaire during 1966-1982 price controls on food to depress real farm wages, as well as taxes on farm exports to provide cheap credit for industry, were designed to encourage indus- try; they cut the growth of food production in half and of export crops by even more. None of these workings of an invisible hand would have surprised Adam Smith. An invisible hand also induces people and institutions to invent and apply technology. The ratio of fertilizer to land prices induced about the same applica

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64 PAUL E. WAGGONER lions of fertilizer in countries as unlike as Japan and the United States. Passing time changed the output per worker and per unit of land similarly in different countries (Hayami and Ruttan, 1985~. By incentives and rules, nations will re- plenish the technology on the shelf and lead farmers to use it or not, sparing land for Nature or not. Nations could choose Draconian rules against expanding cultivation and favoring intensive farming to spare more land for Nature. But they must beware the price of food. Mobs have taught the rulers of Rome, revolutionary France, and modern states that costly bread incites riots. Thomas Malthus foresaw that no sensible politician would do away with farm animals and require people to eat only potatoes. If one includes improved technology in an analysis, the desired outcome can be envisioned without exploding prices. The outcome requires a per hectare productivity rise of 2 percent annually; this target exceeds recent increases and projected percentage rises for US crops but not the rise of global maize yield or of US land productivity from 1950 to 1979. A reasonable analysis can produce an annual decline of food prices of 0.5 percent, which matches the 1900-1984 fall of world prices of the main agricultural products.6 DOES WATER CLOUD THE VISION? Despite the abundance of water overall, its uneven distribution among re- gions and its capricious variation among seasons plague farming. The brute ex- pansion of irrigation grows harder. Nevertheless, opportunities to grow more crops with the same amount of water kindle our hope. People usually see the last oasis and pin their hopes on engineering lining, metering and timing, trickle, surge, and drip (Poster, 1992~. A peculiarity about evaporation creates a paradoxical but even greater op- portunity: Bumper crops consume only a little more water than do sparse ones. Doubling yield doubles water-use efficiency, as we see in Figure 6. Consider irrigation with 450 mm of water. In a survey of Pakistani farms, increasing fertilizer from 20 kg/ha to 100 kg/ha raised yield by 40 percent. Because no more water was used, fertilizer also raised water-use efficiency by 40 percent. Ahmad wrote, "Water cannot be considered to have become a real constraint to meeting the world food supplies as long as there is the scope for manipulation of the various underlying factors for. . . increasing . . . production" (Ahmad, 1987~. Another paradoxical opportunity to make water go further is to supplement rain. Water that supplements rain supplies the fast evapotranspiration that raises water-use efficiency. For example, the water-use efficiency of sorghum in Texas doubled when the water supply raised evapotranspiration from 250 mm to more than 700 mm; water similarly raised the efficiency of maize in five US states (Jensen, 1984) The simplest rationale for irrigation in humid places is that rain provides some of the needed water for free.

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HOW MUCH LAND CAN BE SPARED FOR NATURE? 2,0 1 8 1 ,6 - ~n o 1 ~ , ,c ._ 1 ,0 0 8 0,6 65 750 mm - - - 450 m m --SOOmm -I'" / '~ d .' _1~ id .~ 0 20 40 60 80 1 00 1 20 1 40 1 60 1 80 Fertilizer (kilograms/hectare) FIGURE 6 The complementarily of increasing irrigation and fertilizer. NOTE: The three curves show different amounts of applied water, measured as precipitation in milli meters (mm). HOW MUCH WILL HIGH YIELDS TARNISH THE LAND? If farmers increase their yields with techniques that harm the surroundings, they will spare land, but the external effects may tarnish their victories. Farmers do many things on each area of land they crop. In general, higher yields require little more clearing, tilling, and cultivating than lower yields. Pro- tecting a plot of lush foliage from insects or disease requires only a little more pesticide than does sparse foliage. Keeping weeds from growing in deep shade beneath a bumper crop may require less herbicide per field than keeping them from growing in thin shade. The amount of water consumed is more or less the same per area whether the crop is abundant or sparse, and growing higher yields distills away only a little more water and leaves only a little more residue of salt than lower yields. Seed is planted per plot; choosing a higher yielding variety does not affect the surroundings. If the improved variety resists pests, it lessens the external effect of pesticides compared to a sprayed crop. If the pests in a crop had gone uncontrolled and had decreased the yield, the new variety and its higher yield

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66 PAUL E. WAGGONER would be free, environmentally. By minimally changing the external effects of things that farmers do per area, lifting yields will thus lower the effects per yield. On the other hand, farmers use more of some things to raise the yield of their crops. For example, farmers apply more fertilizer per plot to raise yields. Does this leak more fertilizer into the surroundings per yield? Consider again the complementarily of water and fertilizer (Figure 6~. A given yield requires more fertilizer with 300 mm than 750 mm of irrigation. Consider the yield of 1.4 t/ha. Even an infinite amount of fertilizer and great fallout into the surroundings would not produce 1.4 tons on the field irrigated with 300 mm of water. But 50 units of fertilizer would grow 1.4 tons on the field irrigated with 450 mm of water. The hectare irrigated with 750 mm of water would get the same 1.4 tons from only 30 units and would therefore have less environmental fallout. For a given yield, optimum conditions for growth and high yield lessen the fallout of such things as silt, pesticides, and fertilizer into the surroundings. If factors that must be increased per plot to raise the yield are improved in step, their improved coordination may diminish the fallout.7 STRAWS IN THE WIND Having reviewed some of the elements of farming, we must look at how global cropland and production are actually changing at the macro level. From 1975 to 1990 cropland expanded by only 3 percent, but from 1969-1970 to 1988- 1990 the supply of calories per capita rose by 11 percent (FAG, 1992~. Because of the rising yields, farmers grow surpluses today, driving prices down. To combat the bankruptcy of farmers, prices are supported, and farmers are given incentives to idle their cropland. So far in the 1990s about a fifth of US cropland has typically been idled by government programs.8 The geographers Deborah and Frank Popper have made vivid the reversion of farms to range with their phrase "The Buffalo Commons" (Matthews, 1992~. Looking forward, the Dutch projected changes from the present farmland in nations of the European Union to the year 2015 (Rabbinge et al., 1992~. Diverse scenarios built around liberal trade, employment policies, and environmental regulation all shrank farm- land by 40 percent or more. Straws in the wind hint that land can be spared. A SCENARIO FOR SUCCESS A tally of strategies to lessen deforestation is a good place to start the search for a scenario about sparing land for Nature. A strategy of economic development to attract settlers away from treasured forests takes too long. Encouraging migra- tion to places other than the lands we wish to protect is usually insufficient to deflect immigrants. In the minds and meeting rooms of environmentalists, desig- nating Nature reserves may stop hungry people from clearing plots; but this is not

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HOW MUCH LAND CAN BE SPARED FOR NATURE? 67 the case outdoors. And reserves for extractive but sustainable forestry support few people. On the other hand, eliminating the need to abandon land that is already cleared by maintaining or restoring productivity offers some hope. Ex- periments for eight years on soil representing the Amazon basin grew undimin- ished yields of about 7 t/ha; this productivity has continued over seventeen years for forty crops (Sanchez et al., 1982, 1990; World Bank, 1992~. Because numbers can impart a misleading aura of accuracy, I have written more about directions than precise numbers. In the end, however, the question "How much?" calls for numerical answers and familiar images of space such as India or Amazonia. The plot for my quantitative scenario relates the area poten- tially spared to: 19 A reference area, which I shall set at 2.8 billion ha of crop- land. This is twice the size of the present cropland, six-tenths of the present cropland plus permanent pasture, and a fifth of the land in the world. If farmers use less than 2.8 billion ha as the population multiplies from about five to ten billion, I assert that they spare land for Nature. 2J Diet, with a daily use of calories from agricultural products varying from about 3,000 to 6,000 calories per capita. 3, Yield, which can vary from 4 to nearly 80 million calories (Meal) per ha. Some examples of yields in tons (t) and corresponding Mcal/ha are: wheat in an arid African nation, 1 t and 4 Mcal/ha; wheat in North America, 3 t and 12 Mcal/ha; wheat in Europe, 6 t and 24 Mcal/ha; wheat in Ireland or maize in the United States, 9 t and 35 Mcal/ha; potatoes in Maine or Ireland, 30 t and 18 Mcal/ ha; and maize from the field of the national winner in Pasco, Washington, 20 t and 78 Mcal/ha. The 12 quadrillion calories produced by agriculture plus con- sumption by draft animals, which is shown in Figure 2, divided by the world's 1.4 billion ha of cropland produces an average of about 8.5 Mcal/ha or 2 t/ha. To support ten billion people consuming 3,000 car/day, farmers averaging the yield of wheat in arid Africa would spare none of the 2.8 billion ha of the reference area (Figure 7~. If the ten billion consumed 6,OOO car/day, the yield of 4 Mcal/ha would spread over an additional 2.8 billion ha of other land. On the other hand, an average yield of 16 Mcal/ha, one-third less than present European wheat, would spare much of the land. Averaging 16 Mcal/ha, farmers would be able to support ten billion people consuming 6,OOO car/day on the present crop- land, sparing half of the reference area. If the ten billion consumed only 3,000 car/day, 16 Mcal/ha would spare for Nature about 600 million hectares of present cropland, the area of the Amazon basin. Above 24 Mcal or 6 t per ha, farmers will use little cropland, globally sparing an area of today's cropped hectares equal to the land of India, even when people consume 6,000 car/day. If during the next sixty to seventy years the world farmer reaches the average yield of today's US corn grower, the ten billion will need only half of today's cropland while they eat today's American calories.

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68 PAUL E. WAGGONER 2.8 - U, s 4~ o U) 0 1.4 ._ - o 0.0 \ 6,000 \Calones I Day \ 3,000 \ \Calones J Day\ "India" Spared (0.35\ "Amazon" Spared (0.6) Current Cropland Afri canNorthMai ne WheatAm eri canPotatoes Wheat European Wheat U.S. Corn\ o 2 4 6 Yield (ton grain equivalent per hectare) 8 FIGURE 7. The sparing for Nature of a reference area of 2.8 billion hectares of cropland by farmers raising yields for ten billion people consuming 3,000 or 6,000 calories daily. SURPRISES, BAD AND GOOD Orderly people instinctively turn to experts for projections that will protect them from surprises. Unfortunately, a century of scientific bloopers by heavy- weights beginning with Lord Kelvin disabuses their instinct.9 Looking ahead to what ten billion people might be able to save for Nature, I could be daunted by the experts' historic lack of foresight. I could play it safe by conceiving a list of surprises and writing that "all these might happen." Alas, the forecaster who plays it safe by ending all predictions with "but it may snow" is worthless. Beyond listing surprises that could happen, I must suggest which of them are likely to occur and admit that good as well as bad surprises may be in store. From this list of conceivable surprises, I choose four likely ones: fewer than ten billion people, climate change, new pests, and new breakthroughs. Because growing income and social security have been credited with the slowing of population growth, I look at the speedy economic growth of China and other Asian nations and wonder whether it might check the multiplication of their great populations. The Black Death of the fourteenth century left Europe too small for its clothes, and in 1918 the influenza pandemic left twenty million dead in just a few months. Thus, a surprise like wealth or a pandemic could slow

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HOW MUCH LAND CAN BE SPARED FOR NATURE? 69 population growth. Then, more land would be spared for Nature in the twenty- first century as it was in the fourteenth. Heralded for more than a decade, climate change may not come as a surprise. But just as some unexpected happening is not necessarily a surprise while its specific quality is, so it is with climate change. During a debate about supersonic airplanes, cooling associated with their emissions was projected to have a dire impact. Then, lengthening observations of rising CO2 levels brought projections of warming and drying, with more projections of dire impacts. When the Ameri- can breadbasket turned dry in 1988, the warmer, drier climate seemed at hand. But during 1993, floods in the American heartland discounted predictions made only five years earlier. Computer simulations, of course, had disagreed all along about whether rising CO2 would make North America drier or wetter. I place climate change among the surprises. If cropland in temperate climates becomes hot or dry, yields will fall, and land may be taken from Nature to be used for crops. On the other hand, if cropland that is too cold warms and that which is too dry moistens, yields will rise, saving other land for Nature. Conflicting and changing projections and experience mean we are wise to diversify our portfolios in anticipation of the surprises (CAST, 1992~. Weekly forecasts of pest infestation and the weather affecting them underpin modern pest management. The record shows, however, that pests are shifty, and they may cause disastrous outbreaks and epidemics. New, surprising fungi caused both the Irish potato famine of the 1840s and the Southern corn leaf blight of 1970. "History warns that new pests will appear but provides no data for a model that tells where and when newcomers will appear or what they will be like. The required warning system of sharp, exploring eyes in the field is old-fashioned but remains our most effective approach" (National Research Council, 1976~. Sur- prising pests could lessen the sparing of cropland for Nature. Scientific breakthroughs, or their failure to appear, could also violate our plans and expectations. In Figure 4 yields rise at a declining rate toward a ceiling that is set by crops that are already grown. This projection assumes that societies will continue to encourage, scientists will continue to discover, and farmers will continue to venture toward that ceiling. Disorder from Dushanbe and Sri Lanka to Kigali and Sarajevo to Port-au-Prince and Monrovia renders hopeless encourage- ment by some nations. A decrease in money implies a decline in agricultural research. So, a surprise could arrest the trend that is shown in Figure 4. Yet I would like to point out that some surprises are happy ones. It is opti- mistic but still rational to hope that some breakthroughs will become practice before the population reaches the ten billion mark, surprising me as rising yields after 1900 would have surprised Malthus and even a writer at the turn of the century. The distance between average yields and the actual (not theoretical) 20 tons of grain on the hectares in Pasco, Washington, provides room for a surprise. The surprise of leaps in productivity and new forms of food production would

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70 PAUL E. WAGGONER likely dislocate farming and displace farmers as changes have rapidly and cruelly done since 1940. But it would spare land for Nature. IN THE END If people keep eating and multiplying and farmers keep tilling and harvesting as they do today, the imperative of food will take another tenth of the land away from Nature. So farmers work at the hub of sparing land for Nature. By eating different species of crops and a more or less vegetarian diet people can change the number that a plot can feed. And large numbers of people do change their diets. The calories and protein available from present cropland could provide a vegetarian diet to ten billion people. A diet requiring food and feed totaling 6,000 calories daily for ten billion people, however, would overwhelm the capability of present agriculture on present cropland. The global totals of sun, CO2, fertilizer, and even water could produce far more food than what ten billion people need. Encouraged by incentives, farmers combine natural resources with new technology to raise more crop on each plot, keeping food prices down despite the rising population. Differences in yields among nations and between average and best performance continue to show that yields can be raised much more. For each ton of production, growing more food per plot lessens the fallout of such things as silt and pesticides into the surroundings. If factors such as water and fertilizer are improved in step, fallout may be diminished. Although the uneven distribution of water among regions and its capricious variation among seasons plague farming, opportunities to raise more crops with the same volume of water kindle our hopes for the spread of high yields. Rising yields have shrunk European and American cropland for decades, and governments pay farmers to keep fields idle. Globally, cropland has been roughly level since the middle of the twentieth century. If average fields in the world sixty or seventy years hence, when we are likely to number ten billion, yield as much food as today's potato fields in Ireland, wheat fields in France, or corn fields in Iowa, large portions of the land currently in crops can revert to Nature. This will not happen by itself, nor will it happen if today's scarcity of grain transfixes us. Countering humanity's multiplying population and wealth to spare habitat for Nature requires never-ending research, encouraging incentives, and smart farmers. NOTES 1. This article briefly answers the question in the title. An ample answer with full citation of its foundation has been published as Task Force Report No. 121, by the Council for Agricultural Sci- ence and Technology (see CAST, 1994). Fallout into the environment is more fully examined in Waggoner (in press). 2. Calculated at 2.6 times the weight of feed, containing 4,000 car/kg, to produce 1 times the weight of meat, containing 2,200 car/kg. Feed per meat from US Department of Agriculture (1992).

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SPARED FOR NATURE? 71 HOW MUCH LAND CAN B. s of the US Department of Agriculture's Agricultural Statistics. The nnual diet from 1909 to 1970. usion. . . is that 1,000 billion people could live from the earth if photo- r!" (deWit, 1967). Fallen fertilizer prices are reported, e.g., in Freeport- thesizing 1 to 6 grams of biomass consumes a thousand grams of water. poration from land matches photosynthesis to feed 400 billion. For Gets for 1972-1994 furnished by Ralph Cummings Jr., US AID, and he US consumer price index. See also Abelson (1995). see Binswanger et al. (1985). The analysis, which W. D. Nordhaus Vaggoner (1994). he principle of a factor only raising yield when other factors are not igins of plant physiology and agronomy. Recently, it has been related if intensive farming, as in deWit (1992). ltural Policy Research Institute (FAPRI) tabulated the area planted to United States and the area idled by two programs identified by the 1 CRP. The idled areas have been, or are projected to be, steady from jects them to decline after 1997 (FAPRI, 1992). aws the feet of clay: The Experts Speak: The Definitive Compendium on (serf and Navasky, 1984). When the US president appointed distin- aers to report on technology that would matter to the nation during antibiotics, radar, space exploration, and jet-engine aircraft. "In fact, if he exciting things that happened over the next several decades, they " (Townes, 1991). REFERENCES rational agriculture. Science 268:11. , a constraint to world food supplies. Pp. 23-27 in Water and Water applies, W. R. Jordan, ed. College Station, Tex.: Texas A&M Univer s, eds. 1993. The Bias Against Agriculture. San Francisco: Contem llak, M.-C. Yang, and A. Bowers. 1985. Estimation of Aggregate Agricultural Research Unit Report 48. Washington, D.C.: World ~ institutions work a scientist's viewpoint. Pp. 387-395 in Water and food Supplies, W. R. Jordan, ed. College Station, Tex.: A&M Univer ural Science and Technology). 1992. Preparing US Agriculture for . Report 119. Ames, Iowa: CAST. ural Science and Technology). 1994. Task Force Report No. 121. ~84. The Experts Speak: The Definitive Compendium of Authoritative fork: Pantheon. ~thesis: Its relationship to overpopulation. Pp. 315-320 in Harvesting F. A. Greer, and T. J. Army, eds. New York: Academic Press. ~ use in agriculture. Agricultural Systems 40:125-151. organization). 1992. FAO Yearbook 1991. Vol. 45. Rome: FAO. -e Policy Research Institute). 1992. P. 83 in 1992 US Agricultural .-92. Ames, Iowa, and Columbia, Mo.: FAPRI. 3. See also various yeas book for 1972 tabulates the a 4. "The staggering cone synthesis is the limiting facto McMoRan (1993). Photosyn At this ratio, the global eve details see Waggoner (1994) 5. Expenditures and but adjusted to 1983 dollars by tl 6. For past food prices devised, is reported fully in 7. The annunciation of limiting coincides with the of to the environmental effects ~ 8. The Food and Agricl: fifteen principal crops in the acronyms ARP/PLD/0-92 an 1989 to 1997, but FAPRI prc 9. The title of a book sh of Authoritative Misinformat, guished scientists and engin, coming decades, they missed you were to ask what were missed all of them, every one Abelson, P. H. 1995. Intern Ahmad, M. 1987. Water a' Policy in World Food S sity Press. Bautista, R. M., and A. Veldt porary Studies Press. Binswanger, H. P., Y. Mung Agricultural Response. Bank. Borlaug, N. E. 1987. Makin Water Policy in World sity Press. CAST (Council for Agricult' Global Climate Change CAST (Council for Agricult Ames, Iowa: CAST. Cerf, C., and V. Navasky. 1c Misinformation. New deWit, C. T. 1967. Photosy the Sun, A. San Pietro, deWit, C. T. 1992. Resourc FAO (Food and Agriculture FAPRI (Food and Agricultu Outlook. Staff Report

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