A Short History of the End of Our World


When the current recession ends (if it ends), economic growth will return and carbon dioxide will continue to accumulate in the atmosphere. The current rate of accumulation is about 2% a year, or a doubling to over 700 parts per million in less than 50 years. No one is talking about limiting growth and adjusting developed economies to a new reality. No one is talking about cutting carbon dioxide emissions to a level that would stabilize the amount of carbon dioxide in the atmosphere and slowly let it return to a “normal” level (probably 280 parts per million: the current level is 385 ppm). Such cuts would amount to 70-90% of carbon emissions in the developed world. That is a monumental project that can only be accomplished by reducing energy use—insulating houses, building very efficient cars, motors, pumps, building public transportation. There are also two safe, relatively inexpensive methods of taking carbon out of the atmosphere in large enough amounts to make a difference: converting crop waste to charcoal (biochar) and spreading it on farmland, where it raises soil fertility; and revegetating degraded lands to forests or grassland (land equivalent to current cropland is available). No one is doing either of these on any scale. Most schemes for engineering a lower temperature (seeding the oceans with iron, pumping sulfur dioxide into the atmosphere, launching sunshades) have serious disadvantages. That is, they are either risky or nuts.

As the atmosphere warms, the sea warms (but more slowly) and sealevel rises, partly from more water in the ocean from melting glaciers, partly from the thermal expansion of water already there. A disastrous rise in temperature and sealevel will supposedly occur after a global warming of 4˚ Centigrade (within the generally accepted range of that predicted for 2100 if we don’t control carbon emissions). However, the most recent time carbon dioxide levels were at 350 ppm, sealevel was 80 feet higher, so we may already be there, so to speak, the sea just hasn’t responded yet. What is certain is that the carbon dioxide now in the atmosphere implies much additional warming. The earth responds slowly to the temperature of its atmosphere. Both land and sea have great thermal inertia.

Ecosystems and climates flip. That is, a slow change turns into a new regime. Feedback processes kick in. The forests in the western United States and across the boreal regions of Canada and Russia are collapsing from drought, insect damage and warmer temperatures. Drought stresses the trees, thawing permafrost uproots them, and insects are many times more abundant in the shorter winters and warmer summers. These dying forests will decay, or (more likely) burn, putting hundreds of millions, or billions, of tons of carbon dioxide into the atmosphere. As the permafrost below them thaws, it emits methane and carbon dioxide. So do warming boreal peat bogs. The tundra lakes, filled with water from the last ice age, expand as the ice melts, then drain away, exposing more bare ground to the sun. This soil also emits methane and carbon dioxide. As the sea ice melts in the Arctic, the ocean warms from the sun. Along the east Siberian coast, methane, produced by bacteria and locked in a water/ice lattice by cold and the weight of the sea water, now bubbles up from the seabed. As they warm and dry, the tropical peat-swamp forests of Indonesia burn, as they have been for two decades (burning tropical peat swamps are a major contributor to global warming). The Amazon rain forest burns more frequently and as transpiration from the trees falls, and rainfall fails, begins to collapse. These are all positive feedback processes put in place by a small global warming and, in most cases, some additional human interference.

Melting large glaciers like the Greenland ice sheet or the Antarctic glaciers takes time (millennia or centuries, at least one century, say, for a quarter of the Greenland ice sheet, even under the more calamitous scenarios), so sealevel rise beyond a meter or two by 2100 is unlikely. Mountain glaciers, smaller and fed by yearly snows, melt more quickly. Those in the Andes that water the high terraces of Peru (most cultivable land in Peru is over 9000 feet) are almost gone. When they are gone and ground water levels fall, many crops will no longer be grown. The Himalayan glaciers that feed the great rivers of India, Pakistan and the countries of Southeast Asia, are also melting. Without them, spring floods will be greater and summer flows lower. Much land now irrigated by these rivers will no longer be cultivable. A billion people depend on its crops. Since groundwaters in India are already overpumped, the only way to maintain agricultural production in the subcontinent will be to reconstruct the valley tanks and water structures that once served to catch the monsoon rains. But rising temperatures and a failing or flooding monsoon will soon make that effort difficult, or fruitless.

Except for island nations, sea level rise will be a problem for the future but other things will happen in the ocean. Its rising acidity will cause its fisheries to collapse, as the shell-forming algae at the bottom of food chains die. (All commercial fish stocks are already predicted to collapse from overfishing by 2048, so we may have caught the last fish just in time.) Coral reefs will melt away and animals with calcium carbonate shells (clams, oysters, mussels) will go extinct. Whales and other sea mammals will go extinct. The Gulf Stream will slow greatly or shut down, ending the circulation of oxygenated water to the deep sea and suffocating the animals of the depths. As the sea stagnates, it will become perfused with hydrogen sulfide, a toxic gas. The change in ocean currents and surface temperatures will change weather patterns and make many parts of the earth (the east coast of North America, much of Mexico and Central America, much of South America south of the Amazon, parts of southeast Africa, much of Southeast Asia and the Himalayas) uninhabitable from constant storms, floods and drought.

The land warms more quickly than the sea. Much of the land on earth is between 30˚ north and 30˚ south (that is, about the equator). Some of this is now desert, some tropical forest and savannah. As the climate warms the forests and grasslands will be replaced by desert (though some pockets of vegetation in favored locations may remain). Desert conditions will spread south and north, encompassing most of the United States, southern Europe up to the latitude of Paris, northern South America, most of Africa, India, Southeast Asia and all of China: most of the inhabited world. The boreal forests and tundra of North America and Eurasia be replaced by mixed deciduous woodland and grassland, as the Arctic islands were once covered by redwood forests. Most flowering plants and large animals, unable to migrate quickly enough, will go extinct. The habitable parts of the world, where large animals can live and crops grow, will consist of the boreal regions (an immense landscape, its Siberian section contaminated by radioactivity from the Soviet nuclear program), Iceland, New Zealand, Tasmania, southern Patagonia, western Antarctica, the west coast of Greenland. Some writers imagine high rise cites amidst intensively cultivated stony Arctic soils.

What will happen to people? Most, in both undeveloped and developed parts of the world, will die, probably not catastrophically, but slowly, from starvation and despair, as death rates climb by 15-20%. This happened in Russia (with a lesser rise in the death rate) after the collapse of the Soviet Union, and is still happening there today (the collapse of the Soviet system explains why Russian troops stationed far from their home bases must return in spring to plant, and in fall to harvest, their potatoes). It probably happened with the collapse of the Maya and the Aztec civilizations, from entirely different causes, in Mexico and Central America. Industrial civilization can maintain itself in a desert, desalinating seawater, growing crops in greenhouses cooled by seawater and watered by its sweet condensation, mining copper, fueling itself with solar panels, pumping oil out of the ground, living underground where daytime temperatures average 150˚ Fahrenheit. Would it? As the economic blows worsen, and food, water and electricity become scarce, I doubt whether the retreat from the present will be orderly. Farmers will not plant with perennial cover crops the fields they abandon. For one thing, they will have no money to do so. People imagine an orderly retreat to the Arctic coasts (forget about national boundaries) but this ignores the difficulties of feeding large populations, purifying polluted surface water, maintaining the infrastructure necessary to build roads, power stations, vehicles, cement plants in the north. As the seas rise, the water will flood the containment ponds of abandoned nuclear power stations, where the spent fuel rods are stored (if the water in the ponds has not already evaporated and radioactive material melted into the earth), oil refineries with their stored oil and chemicals, houses with their toxic cleaners and pesticides. This material will spread to river deltas and inshore waters. Public zoos and private animal shelters, will release their animals rather than let them starve: lions, tigers, elephants, camels, yaks may once again populate North America. Tropical plants will escape from botanical gardens into the new tropical habitat. In 20,000-100,000 years, the ocean, finally cleansed of man-made and natural toxins, its circulation restored, will return to something like normal, and after another million years or more, new adaptive radiations will have filled it with new creatures.

Perhaps people will watch some of this, as they wander the corners of the deserts with palms and springs, carrying their bows and arrows, and digging tools scavenged from former human habitations (much of it now under water), and the great savannahs and forests of the Arctic coast.

The Natural History of the Present, Chapter 10

Chapter 10: Europe until 1800: Limits of a Fully Settled Agricultural World

Using the natural production of the forest or waste to increase the fertility of cropland is a common strategy of folk agricultures. It usually depends on domestic animals that eat leaves or grass from the surrounding uncultivated land and whose manure is then used on the fields. In a modern African variant of this system, branches from leguminous trees, grown in hedgerows between the fields, are directly used to mulch, and thus also to fertilize, crops; no animals are involved. The rapid decay rates of the tropics make this system possible.
Overexploitation of systems that depend on the surrounding forest or wasteland for a portion of their fertility is easy. While usually caused by over-population, over-exploitation can also be caused by an increase in market demand for timber, grain or fuel. An example is trekkers seeking food and shelter in Nepal. Villagers build small hotels of native lumber to take them in. They also grow more food to feed them, and more fuel to warm them, thus increasing their income at the cost of over-cutting the forest for timber, fuel and fodder. This increases erosion and the risk of landslides in steep areas. (Much of upland Nepal is steep, its slopes held in place by shrubs and trees; under traditional management, firewood was taken from dead vegetation.) The rise in the number of ski areas in Swiss mountain valleys is a more high-tech example of market-based over-exploitation of steep forestlands (which 250 years ago in the French Alps were cleared for farmland, with catastrophic erosion); now not for food or fuel but (similarly to the Nepalese) for business income. In such cases the demand for wealth magnifies the effect of population.

In the grain-and-cow culture of the Near-Eastern agriculturists who settled Europe 7000 years ago, using products of the wasteland to fertilize fields already had a long history. Fertility of upland fields is maintained on the one hand by in-situ weathering. This is the release of mineral elements from the soil by bacterial and fungal action and the erosive effect of natural rainfall, which is slightly acidic (root secretions make it more so and increase the release of minerals). Fields have much simpler plant, animal, fungal and microbial populations than forests or grasslands, and lack their nutrient cycling ability. Leaving them bare for much of the year exposes them to extensive leaching and erosion. They also have less sophisticated systems for releasing nutrients from soils. Cereal crops use nutrients equivalent to the forests or grasslands they replace, but much of their growth, along with the nutrients, is removed in the annual harvest. Nitrogen in fields is provided by free-living nitrogen-fixing bacteria in the soil, and those living in nodules on the roots of leguminous plants. The annual pulse of nitrogen may be greater in fields than in grasslands or forest, because of the warmer temperatures of the cleared ground. A good part of this nitrogen is leached out by rainfall, even from hayfields, that is, cultivated grassland. The problem is that in such simple systems, the bacterial activity that releases nutrients, and nutrient uptake by the plants, do not always coincide; then nutrients escape. For instance, bacteria may mobilize nutrients before crop plants have been seeded in the spring, or after they are done growing (or have been plowed under) in the fall. The fertility of fields depends on the balance among what is removed—by crops, by leaching, by soil erosion—and on what nutrients are produced within the field or added to it. If the soil is inherently fertile, and soil erosion is not too great, the crops not too demanding, and leaching of nutrients by rainfall remains within bounds, a field will retain a low level of fertility indefinitely. (Temperate loess soils are good here.) But the steady fall in fertility after the clearing of the natural vegetation is the reason for rotating fields back into forest. The earliest agriculturalists in Europe cultivated river floodplains with hoes (such soils were good to begin with and are renewed by floods and by soil washing down from the hillsides), but the slash-and-burn agriculturalists of upland Europe apparently moved on, with their cattle and stores of grain, when the fertility of their fields fell. Denser populations require permanent fields, however, and with the manure from domestic animals the fertility of fields can be maintained. Animals are pastured in the woods and kept nights on the fallow; fed cut branches, hay, and grain straw; and put to graze on grain stubble (where they also deposit their urine and manure). The biological productivity of uncultivated lands is a major support of such continuous grain-growing systems.

The introduction of cattle was a tremendous innovation in Neolithic agriculture. Milk provides 4 to 5 times the protein and energy for the same amount of feed as meat; cattle provide traction power; and manure for grain crops. The development of lactose tolerance in adults (the ability to digest milk usually disappears after childhood in humans) is thought to have increased the number of a person’s descendants several times (perhaps 10). In Neolithic Europe each person needed 20 hectares (48 acres) for cropland, fallowland, pasture, hay meadows, firewood, building material, and forest browse. (Branches were lopped and brought to the animals, sometimes stored in piles by the trees for the winter. This is still done in parts of the Mediterranean.) A village of 30 people needed a herd of 40 cattle, 40 sheep or goats, 13 hectares of wheat or other grain, and about 5 square kilometers of forest for firewood, timber, and animal pasture. As in Medieval times, the cropland (hoeland, plowland: the plow was invented about 6500 years ago on the Sumerian plain) was probably communal and divided into two: one field was used for winter grain, the other rested, its stubble and weeds grazed by the domestic stock, which were also kept there at night. The fallow period allowed for the build-up of nutrients from bacteria, decayed plants, and animal manure.

A variation on this system in medieval and renaissance Europe was provided by the so-called transhumance pastoralists who took their flocks of sheep up into the mountain pastures of the Alps or Pyrenees during spring and summer, returning in fall and winter to the grain-growing lowlands: Spanish wheat growers paid for the privilege of having such flocks kept on their fields for a night or a week (as long as the stubble and the roadside grass would support the animals); manuring by the sheep is thought to have doubled wheat yields. While the manure produced by the flocks came from the immediate surroundings (the wasteland, steep banks, roadside ditches, and grain stubble), the animals themselves were at least partly supported by the mountain pastures and the landscapes in between. That is, their total biomass was much greater than the local landscape would have supported. Sheep are good at converting biomass to dung, producing 10 times their weight in dung annually. So this was a way of bringing the biological productivity of the mountains to the plains and making the mountains useful to people at lower elevations. (All the same, overgrazing during the medieval period by huge flocks of sheep in La Mancha and Estremadura—those impoverished lands that produced the American conquistadores—converted large parts of central Spain to poor quality grass and scrub; and the general decline in Mediterranean forests after the Middle Ages is thought to have been caused by overgrazing by sheep.) Whether such grain-growing systems were sustainable over the long run depended on the underlying fertility of the soil (a gift of nature) and the rate of erosion (a matter of climate, soils and management), but they supported (or helped support) many of the Mediterranean and Near Eastern high civilizations.

The organized settlement systems (an early state capitalism?) of the Greeks, with their colonies in Turkey, Sicily, Egypt, the Black Sea, the Mediterranean coast of France, provided surplus grain for mainland Greece. By 400 B.C. perhaps half the food eaten in Greek cities was imported. Were such colonies a sign of erosion in Greek agricultural soils? Many Greek sites show thousand year cycles of use and abandonment. Cycles of expansion and contraction of agriculture and population during the Neolithic and Bronze ages occurred throughout the Mediterranean basin and central and western Europe, especially on upland sites. As people filled the better soils of the river valleys and lower slopes, the population continued moving up to the poorer soils of the surrounding hills. Such settlement was followed by massive erosion (visible in cores from lakes or swamps), followed by the abandonment of land, depopulation, the regrowth of scrub or forest, until some centuries later, when the soils had rebuilt themselves, settlement began again. Many European and Mediterranean landscapes were thus deforested and cleared several times over 7000 years. Such cycles continued into the classical and medieval periods.

Greek colonies were followed by those of Rome, the citizens of whose capital were entitled to a daily ration of grain, and whose grain-shed included most of the Mediterranean basin. Egypt was called the granary of Rome; there were also the more or less new lands along the North African littoral, in Turkey, and in southern France. Under a law of 111 B.C., any Roman citizen could claim up to 20 acres of public land to cultivate; by bringing it under cultivation he established ownership. This was 10 times the size of the individual holdings Romulus passed out during the settlement of Rome 600 years before, an indication either that agriculture had become more commercial or soils had become less productive. In 750 BC a man with a hoe could cultivate two acres of olives, grapes, vegetables, cereals, and fodder crops. The multistory canopy saved labor, prevented erosion and took half the land to feed the same number of people as plowing with an ox; but for large landlords plowing with an ox was more profitable. At any rate cultivation in Italy expanded; the land near Rome, once full of orchards, became large grain-growing estates, and then, as the soil declined or eroded away, uncultivated wasteland. Wood use in Rome has been estimated at 1 to 1.5 cubic meters per person per year, in total about the wood in 30 square kilometers of forest. Is such a number high or low? Per capita wood use in North America before the Revolution was 17 cubic meters a year, about 4.5 full cords, that is 11 to 17 times as much. (Two hundred years later modern people in the northeastern United States use 4 to 5 cords per winter to heat their houses; less than 1 cord if their houses are super-insulated.) Deforestation for metal smelting, pottery-making, brick and lime burning, building material, for new agricultural land, for pastureland, meant the continuous exposure of bare and overgrazed soils to the elements; and led to slow, massive, cumulative soil erosion. Composting, crop rotation, and the use of manures in maintaining soil fertility were known to the Romans (and probably to earlier peoples: the slow charring of vegetation, along with composting, began producing black earth soils in the Amazon Basin 2500 years ago), but such practices were not widely followed, and soil exhaustion and erosion imposed long cycles of settlement, abandonment, and re-settlement on river valleys throughout the Mediterranean, and influenced the larger empires of which they were a part (thus, the colonies, the importation of grain). Many former Greek and Roman port cities now lie several kilometers from the ocean. Some of this erosion would have occurred without human intervention, as the Mediterranean climate became drier, and the landscape more susceptible to erosion from its intense rainstorms, but human manipulation of the landscape speeded things up. Some Mediterranean uplands have little soil left to erode. The vine and olive, with winter wheat on flat ground, the tree fruits that date from Roman times (many brought from Persia), and the sheep pastured on the aromatic but not very palatable herbs of the once forested mountains of Crete or Lebanon constitute the modern and beautiful Mediterranean landscape. Springs and streams dry up in summer; the total run-off from the landscape is greater. On hilly land near Rome, farmers plant hazelnuts by blasting small holes in the light volcanic rock, then plant the shrubs, and water them until they take or die. Those that die (perhaps half of the first planting) are replanted. No natural topsoil is left. Such persistance constitutes land rehabilitation: the re-creation of soil with dynamite, tree roots, tree litter, hope, and hard labor.

The agricultural remaking of Europe has left various signs, some of which we can read. Pollen cores from English ponds show pollen of oaks replaced by that of weeds, wheat, rye, hazel and birch. Hazel and birch are early successional species; hazel was often coppiced for fuelwood, that is, cut at short intervals from stands that sprout from stumps. Agriculture, by baring and stirring the soil, mobilizes the soil’s lead in airborn dust. Airborn lead from Roman silver smelting shows up in cores from the Greenland icecap. Cores from peat bogs in the Jura Mountains of France show variations in airborn lead in the surrounding landscape over the last several thousand years. An initial rise 8000 years ago corresponds with a volcanic eruption in France. Soon afterward Neolithic agricultural activity tripled the relatively constant, post-glacial background level. A further rise in lead 3000 years ago corresponds with smelting at Phoenician lead mines in Spain. There were rises corresponding with Roman and Greek metallurgical activity (a layer of lead from Roman silver smelting is found in lake muds all over Europe), a decline from those heights in the Middle Ages, and a rise with the Industrial Revolution that peaked in 1905, the rise in this case caused by coal burning as well as metal smelting. Total airborn lead peaked again in 1967, from lead in gasoline, on top of all the other sources, when it reached 85 parts per million. The post-glacial background concentration was 0.28 parts per million. So anthropogenic lead in the modern atmosphere is something like 250 to 300 times that of the hunting and gathering background, that to which one assumes modern people and animals are adapted.

The two-field system helped support Greece and Rome. The fields, fallow or cropland, were plowed in spring, summer and fall (they were planted in the fall). Together with Egypt’s Nile Valley, and some irrigated lands, the two-field system supported the Islamic civilizations of Turkey, the Middle East, and North Africa. (“Some irrigated lands” includes lands watered by qanats, underground tunnels that collect groundwater from mountain slopes. Qanats are found in the Middle East, Cyprus, Iran, Central Asia, and in parts of North Africa. Their design makes them self-regulating, though they must effect surface waters. Their flow in Iran in 1960, to provide urban water and to irrigate farmland, has been estimated at that of 12 Nile Rivers. For the most part qanats have been replaced by pumps, that is, water taken from deep wells and rivers, but the cities of Bam and Irbil still use water from qanats dug by the slaves of Sennacherib 2700 years ago.) The two-field system supported the civilization that followed Rome in Europe north of the Alps: its surpluses (wheat yielded only twice the seed sown) built Romanesque churches, fortified castles, early walled towns. About 800 A.D., when Charlemagne was crowned king of a united Europe in Aachen, a three-field system had come into use in some villages in northeastern France. The common ploughland was divided in three parts. One field was planted in autumn with a winter grain (wheat or rye); this is the traditional method of Mediterranean or Near-Eastern agriculture that had been brought to Europe several thousand years ago. Another field was planted in spring with a summer crop of oats, barley or peas (the last a nitrogen-fixing legume); this was new. The third section was left fallow. This system increased total crop yields, putting two-thirds of the plowland into crops yearly. It increased the land in crops by a sixth. It also increased crop variety, provided more fodder for the animals and spread work more evenly over the year. More fodder meant more manure and greater yields, a positive feedback. In later centuries a winter fodder crop, often turnips, would be planted for the animals.

The re-settlement of Europe that followed the crowning of Charlemagne was intended to remake the European landscape into a holy and cultivated earth. Charlemagne renamed the months (then, as now, named for Roman gods and goddesses) for their agricultural activities (the month to plow, the month to plant, the month to cut wood). Around 1000, the wheeled iron plow, pulled by a yoke of 8 oxen, came into common use. This implement, invented several centuries earlier, made possible the conversion of Europe’s heavier soils (the clays on which the oaks grew) to agriculture. The invention of the shoulder harness and the nailed horseshoe led to the growing use of the horse for traction power. Horses are several times more expensive to maintain than oxen and must be shod to protect their hooves from the northern European damp, but can exert more force and work faster for a longer time. Such developments in agriculture opened up new lands in Europe and by 1100 led to prosperity across the continent from the Atlantic to the Dnieper. The 1100s brought the first European manufacturing age, powered by wind and water mills. Europe had abundant resources of wood, flowing water and minerals. Water mills were used to mill grain, full cloth, process hemp, for tanning, laundering, milling logs, crushing and grinding ores, sieving, turning, polishing, stamping, for iron-making (operating bellows, puddling and beating iron, drawing wire). Watermills averaged one per 50 families in England.

So the Dark and Middle Ages that followed the death of Charlemagne were a time of boom: in population, in land clearance (sometimes of land abandoned after the collapse of Rome), iron manufacture, stock raising, the founding of new towns. Fields were 5% of Europe in the sixth century, 30-40% in the later Middle Ages. Religious orders established monasteries in the wilderness and granted colonists their forestland to clear and cultivate. Interested in increasing their income, the nobility also established colonizing settlements and began the reclamation of marshland and heath. Forest cover in Europe was reduced from 80% (95% originally) in 500AD to 50% or less in 1300. (Some writers claim only 20% of the forest was left by 1400, that in France perhaps 25% of the forest remained.) That forest was heavily exploited for fuel and timber. Land use had fallen to 2 hectares per capita from 16 to 20 in Neolithic times. The climate was also good. During the so-called Medieval Climate Optimum (from about 1000 A.D. to 1400 A.D.; some writers now put it a century earlier) temperatures in Europe were about 1º C. warmer. This lengthened the growing season by a month. The climate change was worldwide. The warm period in Europe coincided with a warm period in the Arctic (southwestern Greenland was settled by the Norse and grain was grown in Iceland), while most of the earth was slightly cooler and civilizations in Central America, the Andes, and the American Southwest collapsed from droughts.

Population in Europe doubled from 1000 to 1220, from 38.5 million to 75.5 million; from a base of 18 million in 600. New land was gone by 1300, and the population was reaching the limits of its renewable resources. Overall yields fell as more and more marginal lands were brought into cultivation; wages fell. By 1300 Europe’s expanding population had overwhelmed its productive capacities. Trade was still a small part of the economy, which was largely agricultural. Roads were poor and travel unsafe. Religious views discouraged much economic activity (for instance, lending money at interest—usury—was a sin). Land in the medieval economy was held by right of occupation and was difficult to sell. Labor could be hired but was governed by a customary web of rights and obligations. Many of the so-called prerequisites for economic growth did not exist. These include secure property rights, the rule of law, more or less working markets, some social mobility, a desire by the individual for financial improvement. The Hundred Year’s War, a general European war, began in 1337. Catastrophe arrived 11 years later as a plague. The plague turned out to be a blessing in disguise.

Europe in 1300 still depended on renewable resources. The primary limit was food. Production per acre would rise 2.5 times during the succeeding centuries, with better forage crops and legumes, animal breeding (which produced more milk or flesh from the same amount of feed), more complex rotations, new crops and animals from Asia, Africa, India and the Americas; but yields never kept up with population, and periodic starvation in Europe continued until the Industrial Revolution. Death from famine and cold were common in Europe in the 1700s. Many episodes of starvation were local, a matter of food distribution rather than absolute shortage (as is still the case in Africa now). The last famine in Europe caused by an absolute shortage of food was in the early 1800s, when the eruption of Krakakoa in Indonesia injected enough dust into the stratosphere to cause two years of climate cooling worldwide. In New England in the year following the eruption, frost occurred in every month. The Irish potato famine, which followed this, was not caused by an absolute shortage of food (Ireland exported food throughout the famine), but by the failure of the British government to distribute food to a starving population. The Irish famine was an unexpected problem of industrialization: that of the introduction of new organisms to new environments. The blight that destroyed the potato crop was brought to Belgium on American seed potatoes imported by steam ship. The rapidity of the trip across the Atlantic allowed the fungus to arrive on the potatoes alive, and the damp summer that followed allowed it to spread all over northern Europe.

Another renewable limit was fuel. Until the 1700s (earlier in England) wood was the primary fuel used for industries and crafts, as well as for cooking and heating. Brick burning, glassmaking, iron smelting, salt evaporation, lime burning, sugar refining, soap making, brewing all required fuel. Heating and cooking probably required the most. Shortages made wood expensive; in 1600 the average city dweller in France spent 10% of his income to keep a fire burning in one room for part of the day. In general, from 1500 to 1700, 7.5% of an ordinary budget went for light and heat. (More efficient brick or stone heating stoves in central and northeastern Europe made it more comfortable in 1700 to winter in Warsaw than Toulouse.) Timber was necessary for buildings, tools, ships and furniture. Hazel and oak, species that sprout well from stumps, were cut on short-term rotations to provide fuel and also materials like tanbark. Some oak stems (the standards) were allowed to mature for timber. But supplies were limited to what forest growth provided. In the European wars of the eighteenth century, English blast furnaces, needed to forge cannon shot, could only operate intermittently; when they ran out of charcoal, they had to shut down. (Eight tons of wood made two tons of charcoal, which would smelt just under a ton of pig iron.) Similar shortages occurred all over Europe. Since iron making depended on a renewable resource, production of iron had to remain at or below what the wood supply could handle. If production were increased to meet an increase in demand, the supply of wood in the future would be reduced. Future production of iron would have to be lowered, or stopped altogether. Everything depended on the growth of the trees, which put an inexorable limit on production. Where available, coal could be used for cooking, heating, and processes such as brewing that simply required a source of heat. Coal was commonly used for such purposes in England, where wood shortages developed early and coal was abundant. Coal had largely replaced wood for household heating and cooking in England by 1700. The adaptation of essentially unlimited European coal supplies to iron smelting was a fundamental factor in the rise of the Industrial Revolution.

There were other problems related to an overexploitation of a renewable environment. One of the more serious was soil erosion. This reduced soil fertility (nutrients were lost with the soil and the depth of topsoil was also reduced); caused the siltation of streams, which increased flooding; and ruined freshwater fisheries. (The gravels in which the fish laid their eggs silted over. Mill dams also destroyed fisheries. Riverine fisheries were failing in Europe by 1000 and were replaced by the cultivation of fish in ponds — many fishponds in the 1100s and 1200s were the dammed sections of rivers and streams, but with different species of fish.) Eroded soil also filled waterways and harbors. Harborworks of cities in the Rhine delta suffered. Bruges in present-day Belgium, the commercial center of northern Europe in the 1300s, watched its harbor on the Zwin disappear, silted past the ability of the city to clear it. Rivers were also polluted by metal works, dye works, tanneries and sewage. Wells were polluted with seepage from cesspits and from rotting bodies in churchyards. The smell of cellars about the cemetery of Les Innocents in Paris was notorious.

Overfishing followed population growth, as marine fish began to replace freshwater fish in the European diet; the trawl was invented in the 1300s, with disastrous effects on fish stocks and the life of the seafloor. With the trawl, cod off the English coast became so easy to catch that the surplus was fed to pigs. Diking to reclaim land in the Rhine Delta caused major losses in sturgeon, once a key item in the European diet, by destroying its spawning habitat. By 1500 stocks of herring in the Baltic and of cod in the seas about Europe were failing. (Except for the Danish herring fishery, which collapsed with finality in the 1300s, the cod and herring fisheries would recover to fail again.) The Baltic and North Sea herring fisheries originally amounted to billions of fish annually. Fish was one of the sources of wealth of the cities of the Hanseatic League. (Even in the late 1600s, work in the herring fishery constituted 20% of the Dutch economy.) In the late 1400s fishermen from Bristol sailing west of Iceland discovered the Newfoundland cod fisheries. Did they stop to take on some of the Norse colonists in southern Greenland, whose culture was failing? By 1600, 20,000 European fishermen were salting and drying cod off Newfoundland. Dried cod from the North American banks would provide a cheap source of protein for Europe for 500 years.

Until the Industrial Revolution, the European world was Malthusian. That is, its population tended to increase faster than its food supply. In a downward spiral, more people meant more demand for grain, less crop rotation, less fodder for the animals, not enough manure to raise grain yields, the animals dying from parasites and malnutrition in late winter and spring. People died from hunger and exposure. Infant mortality was 25-30% until the late eighteenth century, life expectancy was 30 to 40 years, epidemics were common, most of the population was undernourished and depended on vegetable foods (bread, gruel, potatoes). Much of the population was very poor. At the time of the French Revolution, 80% of the population of France is thought to have been poor or destitute; that is, they owned the clothes on their backs. Many were more or less homeless, not being able to afford both food and lodging. In Medieval and Early Modern Europe four-fifths of disposable income went for food. The nobles and the members of the middle-class ate well. These distinctions lasted in England long into the period of industrialization: in 1800, boys taken into the Royal Navy from the slums of London or Liverpool were 8 inches shorter than boys from the upper classes; in 1940, working class draftees were still 4 inches shorter than boys who had gone to elite schools. So one could recognize an officer by his stature. Until about 1700, periods of growth in the standard of living of the common people were followed by periods of reversal (the long waves in the economy were cyclical), so the standard of living of an agricultural worker in Europe in 1500 or 1600 was only slightly higher than in Roman times. When Europeans came to North America, where food was plentiful, their numbers, instead of doubling every 150 years, began to double every 23 years. (Most of the first-born children in Puritan families were illegitimate.)

This is not a portrait that leads to a progressive view of history (constant progess onward and upward). That view would come out of the cascading improvements in material life with the Industrial Revolution (railroads, steam power, gas lights) and their consolidation and elaboration in the twentieth century (electricity, cars, radio, penicillin, TV). In the United States, more egalitarian and less bound by social traditions than Europe, especially after the Civil War, markets expanded with the population and economic productivity grew at 2% a year from 1870 to 1970. (In general, a more widespread prosperity increases the rate of economic growth.) But it is also not the whole picture. From 1200 to 1800, during a period of worsening climate, agricultural yields in Europe rose 2.5 times, while population rose 10 times. Land under cultivation increased several fold. During the so-called Little Ice Age, from 1430 until 1850, the climate was 1º - 2º C. lower than during the Medieval Optimum. A severe famine from 1315 to 1322 may have set the stage for the Black Death of the 1340s and 1350s (fetal malnutrition interferes with the development of the immune system) and killed outright perhaps 10-15% of the population. The Black Death killed a third to a half of the population. Recurrent epidemics followed for the next century and there was another famine in the 1430s. For the most part crops near their natural temperature limits (at high altitudes or latitudes) failed. During the Little Ice Age cereals could no longer be grown on the hills of northern and western Britain, glaciers and the tree line descended in the Alps, and the northern limits of vinyards in France and Germany retreated 300 kilometers south. Yields of grain on newly cleared land during the warm summers of the Optimum had been twice those of late Roman times but inevitably fell as soils eroded and fell further as the weather worsened. Most of the cooling took place in winter (this was a time of ice-skating and ice festivals) but summers were also 0.8º C. cooler.

After the calamitous 1300s, with disease, famine and continual low level war, came a period of recovery. Europeans rebuilt their water mills for water-powered industry. Tenants gained heritable rights to their land in return for rents. Some common lands began to be enclosed to create rentable tracts. (In the late 1500s, it was said a living was three acres and a cow. People were still saying that in upstate New York in 1850.) Towns, supported by agricultural surpluses, grew into small industrial centers. Industry in late medieval Europe was for the most part cloth, of wool or linen, woven on hand looms at home. By establishing chartered political units, surrounding themselves with walls, and mobilising their citizens into a defensive force, towns established a degree of political independence, both from the church (many towns were founded as the seats of bishops) and from the countryside and the nobility that ruled it. Intellectual life bloomed as paper replaced skin parchment in books (paper was 13 times cheaper than parchment at the time) and printing (also much cheaper) replaced hand copying. Books became more affordable; before the printing press, a professional man’s annual salary bought two cows or four books (and nothing else). After the printing press, a middle class person could afford a couple of books a year. As land became more valuable, property rights became more exclusive, and began to extinguish the traditional rights of the nobility, such as that to ride or hunt where they pleased, and those of the peasantry, which included the right to common grazing land and to fuelwood gathered from the forest. Trade spread once again (memories lingered of the fairs of the 1300s), its bankers and merchants operating under the protection of the towns. Some of this trade was for commodities like Baltic timber and grain and some for luxury products like the silks and spices of Asia, to which the caravan routes, closed for some centuries by drought and the expansion of Islam, were once more open. Imitating the nobility, families of the middle class tried to keep their wealth through such devices as late marriage (thus limiting their fertility); by advantageous marriages between families; or by restricting inheritance to first-born sons. A writer has said that among the wealthy, population control was positive, while among the poor, population was controlled by starvation. In Paris at the time of the Revolution one-quarter of all children are thought to have been abandoned for adoption. Such infants were taken in by church orphanages, where the great majority of them died.

The medieval boom had ended with the famine of 1315 to 1322. Every season of 1315 was wet. Crop yields were half of normal. Hay was put up wet and rotted in the barns. During the winter and spring of 1316 people ate their seed grain. The year 1316 continued wet with another crop failure. The price of wheat tripled, when it could be bought. The famine continued until 1322. Twenty-five years later, after several warm, wet springs favorable to the spread of plague among the rodents of Central Asia, the Black Death arrived with people on ships from trading posts on the Black Sea fleeing the Mongol invasion and killed a third or more of the population of Europe. Parts of Europe would not see the population reached during the Climate Optimum for another 450 years. But the decline in population was followed by a period of development and prosperity: the Renaissance. The average age of death for adults was still something like 35. Still hemmed in by the Islamic world, Europe began probing its limits. Genoese bankers (who had financed the trading cities on the Black Sea) now financed Portuguese explorations around Africa to the Spice Islands of the East and out into the Atlantic, where large semi-tropical islands were discovered. New crops had been appearing in Europe thanks to trade with Asia and contact with the Moors in Spain; these included rice and sugar cane and the new livestock of silkworms. After 1492 came American crops. The yields of Mexican corn and Andean potatoes would dwarf those of European grains. A writer has speculated that the introduction of maize, peanuts and manioc from the Americas to Africa, which substantially increased the human population there, made the trans-Atlantic slave trade possible. New diseases (such as yellow fever) came with trade and with the Africans to Europe and the New World.

The high point of European row-crop agriculture was reached in England in the eighteenth and nineteenth centuries. The development of rotations between cereals and crops of legume hays (which raised the yield of grain per acre), the raising of animals on legume hays (which increased the numbers of animals that could be kept), and the use of animal manures on the fields (which further raised the yields of grain), together with plant and animal breeding that resulted in higher yielding varieties of plants and animals (more meat, wool, or grain for the same nutritional input) — all raised European upland agriculture toward the heights of successful overflow agriculture (such as in the Nile Delta), the ditched fields of Tiahuanaco, or paddy rice. That is, it became a high-yielding, self-sustaining agricultural system, less dependent on inputs from the wasteland, capable of supporting many more people per acre. Enclosure laws in England, enacted partly to ensure an adequate supply of manure for cropland (the relation of pastureland to cropland is important in manure-dependent cropping systems), better equipment, and better capitalized farms put many agricultural laborers and small tenant farmers out of work; some went to poorhouses, some to Australia or the Americas, some to work in the shops of the Industrial Revolution. Agricultural prosperity showed in that in the 1800s horses replaced oxen in Europe as the main source of agricultural power. (Horses are able to work faster for a longer time but are several times more expensive to maintain.) Environmentally speaking, such mixed agricultures were a high point of upland agriculture; they were sustainable as long as they occupied a more or less limited place in the larger ecosystem. Similar agricultures flourished briefly on the American prairies, and in the German settlements of the Shenandoah Valley of Pennsylvania and Virginia. One finds them still among the American Amish.

What ended the European dependence on the renewable world was the use of fossil fuels. England was the European nation most short of wood. It was largely deforested, probably not for the first time, when the Domesday Book was compiled in 1089 AD. (For instance, deforestation of the English downlands had begun in Neolithic times 5500 years before and had continued through the Roman invasion of AD 43. Deforestation, erosion and grazing converted the original downland woodland of oak, alder, willow, hazel, birch and rowan into the thin-soiled grasslands of today.) England was also the country most in need of wood for its imperial ambitions and it was here the Industrial Revolution began. (While some developments came from the continent, the English most thoroughly exploited their economic possibilities, probably thanks to their better developed markets.) A writer has summarized the reasons for the development of the Industrial Revolution in Britain: the greater size and efficiency of British markets (many of the export markets created and maintained by Britain’s sea power); Britain’s commercially minded society; Britain’s openness to innovation; and its accumulation of natural resources from around the globe (also a function of its sea power). In the late eighteenth century machines were developed that, powered by water, would spin cotton thread; other machines wove the thread into cloth. The mechanical advantage of the machinery was so great, the multiplication of the value of the labor and investment so enormous, that the major limits on cloth manufacture became the availability of waterpower, of raw cotton, and of the ability to market the cloth. The manufacturing process was so cheap, compared to hand spinning and weaving, that the manufacturers were able to lower the price until demand met supply. Once cloth fell within reach of the poor, an enormous market was created and demand exploded. Profits were still enormous. The invention of the cotton gin, which mechanically cleaned cotton (previously slaves had picked out the seeds by hand) had a similar advantage: one didn’t just double or triple the value of labor, one increased it by orders of magnitude, powers of ten. During the 1780s, as the English were losing their American colonies, industrial growth in England rose from 1% to 4% a year. It remained near 4% (some writers claim 2%) for a century.

It was the use of fossil fuels to smelt iron ore and power steam engines that finally changed everything. In England in the late eighteenth century processed coal (coke), rather than wood, was first used successfully to smelt iron ore. Unprocessed coal had too many impurities compared with charcoal and the iron smelted with it was too brittle. The coke-making process eliminated these. Coke was much cheaper than charcoal. And coal to make it was available for the mining, as was iron ore. Coal fired the steam engines, made of coke-smelted iron, that pumped the water from English mines and let the miners produce more coal. Coal-powered locomotives, built of iron and running on iron rails, hauled coal and iron ore to where they were needed. Coal-powered spinning machines took over from water-powered ones, removing another constraint from the manufacture of cotton. Coal was later joined by oil and natural gas, useful because they were fluids rather than solids, and so flow under gravity or pressure. Such fossil fuels became unlimited sources of energy in an otherwise renewable and limited world. Fossil fuels will likely remain available for a long time. (For coal the current guess is another 200 to 400 years.)

Coal-powered steam engines eliminated the limits set by floods or frozen waterways in water transportation, by replacing canal and river traffic with rail. In the 1860s coal-powered steamships, built of coal-tempered steel, carried three times the cargo twice as fast as sail. With transportation faster and cheaper, Europe reached out to the rest of the world for its resources. From 1860 to 1920 one billion acres of new land was converted to agriculture, 40% in the United States (much of it in the Corn Belt), 20% in the Russian Black Earths, 20% in Asia. Grain was imported from the “new lands” in the Ukraine, North and South America, and Australia. (Land clearing would continue, with another billion acres added to agricultural lands from 1920 to 1980, mostly in Latin America.) Refrigeration and pasteurization of milk made milk more saleable and its production rose enormously, with beneficial effects on the European diet. Milk now constitutes 20% of the value of agricultural production in Europe and the United States. Imported fertilisers such as rock phosphate and Peruvian guano increased the fertility of European soils. But it was primarily cheap imported food, its cheapness made possible by the exploitation of fossil fuels, that ended starvation in Europe. The pre-industrial European diet in 1800 was worse than that of the European hunter-gatherers of 12,000 years before. The diet worsened further during the early years of industrialization (the average height of men in both America and Europe fell in the 1830s) but improved after about three generations of industrialization. (By the 1920s the shortfall in height was gone.) By 1900 England was importing 80% of its grain, 75% of its dairy products, and 50% of its meat.

Coal also made the chemical industry possible. Coal provided the energy to run the reactions; while coal, oil and natural gas replaced wood as a feedstock. The Haber process, which synthesizes ammonia from atmospheric nitrogen, led to the manufacture of synthetic nitrogen fertiliser, which further increased the yield of soils. Artificial fertilisers and further developments in crops and animals would make Europe nearly self-sufficient in food by the mid-twentieth century. However the excess nitrogen used on crops would cause tremendous pollution problems. Anthropogenic nitrogen lies behind the biological degradation of marine estuaries and (along with phosphorus) of fresh waters. Nitrate pollution in the Thames and Rhine are now two orders of magnitude (100 times) above the mean values of unpolluted streams. (Not all of this is due to agriculture; some nitrogen and phosphorus come from sewage effluent and some nitrogen from the combustion of fossil fuels.)

By the end of the nineteenth century coal was being used to generate electricity. By two decades into the twentieth century coal and oil had produced the modern world, where the problem is not that of producing enough, but of creating demand for all that can be produced. Through gaslight and electricity, fossil fuels had eliminated night. They ameliorated the seasons through heating in cold climates, cooling in hot ones. Fast, cheap transportation eliminated the agricultural seasons, so that now any modern expects fresh fish, fresh lettuce and fresh grapes to be available anytime, whenever he or she wants them. The human habitat in developed countries, even in rural areas, is almost entirely a built one, of roads, telephones, powerlines, fields, houses, internet communication. The cost of food has kept falling until it is now less than 10% of income in developed countries. Such development comes at a cost. In 1850 every Englishman used the equivalent of 1.7 tons of coal a year; this rose to 4 tons by 1919, where it remained until 1950, despite considerable economic growth, when the number began rising once again. Such energy use brings us other problems. But the notion of man’s independence from nature and its constraints is a hallmark of the modern.

The Natural History of the Present, Chapter 9

Chapter 9: Were Ancient Marketable Landscapes Sustainable?

Westerners are taught that civilization began in the Fertile Crescent of Mesopotamia. This is a matter of cultural focus, for while agricultural civilization reached a more extensive development in Eurasia at an earlier time, agricultural development elsewhere began not much later and eventually reached comparable levels. But those agricultural civilizations (say, in the Americas, or in highland New Guinea) did not lead in a straight line to the modern West. Rather they were all taken over by that bellicose, capitalist, Christian culture that rose in Europe over some 1500 years out of its Mediterranean and Near Eastern roots.

In Mesopotamia, the adoption of agriculture seems more obvious than in many places. Wild annuals like emmer wheat and barley grew in large natural stands; for wild crops, they were exceptionally large-seeded. These plants formed a natural climax in the wet winters and long dry summers of the eastern Mediterranean, in micro-climates where the length of the summer drought made the support of woody vegetation difficult. Especially on fertile sites, these tall annuals grew quickly and used up the available soil moisture, preventing percolation and out-competing trees and shrubs. Their seeds were adapted to survive the long summers and sprout and grow quickly in the returning winter rains. A ton of seeds per hectare could be gathered with a hand sickle from such wild stands. The warming and drying climate at the end of the Pleistocene greatly expanded the range of these plants altitudinally. People could harvest them from month to month as summer proceded up the mountain terraces, and store the surplus. The Middle East also had many other of the wild precursors of modern crops, especially the pulses (the protein-rich lentils, peas, chick-peas and bitter vetch); and also flax, whose stems produced a fiber and whose seeds produced an edible oil. Combining grains and pulses in a dish produces so-called complementary proteins, a mix of proteins that corresponds more closely to what the human body needs—not as good as animal protein, but much better than grains alone: so one has wheat and chickpeas, rice and beans, beans and corn. (Chickpeas also contain tryptofan, a precursor of serotonin, which improves performance under stress and promotes ovulation.) Wild cows, sheep, pigs and goats also lived in the area; animals that were domesticable because of their tractable natures and herding or flocking behaviors. (Other crops soon included barley, oats, grapes, olives, dates, figs, apples, pears and cherries.) So here one can more easily envision how an increased birth rate, thanks to a more sedentary life based on acorns and pistacios, and also on gathered cereals and pulses, carried down to the village in woven woolen bags lashed over the backs of goats and sheep, led to an upward population spiral that then led to more settled agricultural communities: permanent fields, domestic animals (pastured after harvest on the fields), stone or mud-brick dwellings, pottery-making. Such villages, based on hoe culture of grain and on domestic animals, existed in upland Mesopotamia 9000 years ago in areas with sufficient rainfall. By 8000 years ago, in what is now central Jordan, such communities were being abandoned, partly because of soil exhaustion and deforestation, and partly because of a drought associated with another breakdown in the North Atlantic circulation, this one caused by the final meltdown of the Laurentide Glacier in North America. With the end of that drought about 7000 years ago, Europe entered a climatic optimum that lasted 2000 years.

The progression to agriculture is less obvious elsewhere. In eastern North America the Hopewell mound-builders of the Ohio and Illinois valleys were cultivating seven crops about 2500 years ago. Four of them were grains with tiny seeds but good protein and fat content; the other crops were a squash and a sunflower grown for their seeds, and sumpweed, a large oilseed, whose pollen and leaves are often irritating to people. These crops were grown on the floodplains of the rivers after the flood had receded. While seed crops provided a considerable part of the diet, the people in the Hopewell cities also ate fish, shellfish, deer, migratory waterfowl, turtles, passenger pigeons, and wild nuts. They have been called cities of hunters and gatherers. (Cahokia, a later mound-building city near present-day St. Louis, was based on maize. Cahokia was a city of several thousand small farms, apparently without significant trading relations with other places.) Shellfish were very abundant in Middle Western rivers. Nuts and acorns had been important foods for people dwelling in the mesic forests of eastern North America for thousands of years. Most acorns have to be leached of their tannins to be edible. Hickory nuts were pounded shell and all in a mortar, the mass boiled in water, and skimmed of froth and particles of shell. Further boiling reduced the mass to a nutritious, storable paste: hickory milk. In the late 1700s John Bartram watched Creek families in North Carolina store hundreds of bushels of hickory nuts. While corn would transform life in aboriginal North America, the domestication of corn in highland Mexico took thousands of years. The plant that became corn was grown for several thousand years before its seeds became usable as a grain. Corn may have been first grown for its sweet stalks, fermented to make beer. (Modern maize stalks are 16% sugar.) An entire ear of Teosinte, the plant that was turned into corn by generations of middle American women, has less nutritional value than one kernal of modern maize. It took many more years for corn to change its daylength characteristics from tropical to temperate and move north. The advantages of corn over the native domesticates were immediately apparent, and when corn appeared, the tribes adopted it. Corn changed social structures; many societies became more hierarchical and their villages larger. In the Asian subtropics, the cultivation of paddy rice involved the invention of a method of cultivation. The method is not obvious. (The cultivation of upland rice is another matter.) In these cases the immediate advantages of agriculture were more difficult to see, and the process that led to a settled agricultural life more difficult to imagine.

In the Near East, irrigation societies and large cities (50,000 people and up), with their organized hierarchies of nobles, priests, courtiers, warriors, artisans and farmers; their massive public buildings of brick, mud-brick or stone; their calenders based on astronomical observation; their use of writing; and war for the purpose of gaining land and tribute, developed after some thousands of years of upland village agriculture. Early cities were storehouses for grain: a means of distributing food, trading for it, and storing it against a risk of crop failure. (One can regard modern cities as means of maintaining and distributing wealth.) These societies exploited a new environment: the flat and arid Mesopotamian plain, with its high summer temperatures (40º C., 104º F.), high evaporation rates and relatively impermeable soils. Initially agriculture here consisted of the cultivation of rainfed winter grains, but the shift of the Indian monsoon south about 5800 years ago reduced winter rainfall so that winter crops would no longer grow. The timing of high water meant that irrigated crops would have to be grown in the hot summer. So more water was needed and soils accumulated salts more quickly. Irrigation produced a more apparently controllable supply of water than rain (it depended on the reliabability of the river’s flow patterns), and a much larger harvest per unit of land. The agricultural work was seasonal. In the off seasons, farmers could extend and maintain the irrigation system. Thus the surplus per farmer was considerably more and the other levels of the society considerably richer than in the upstream societies that still depended on rainfed agriculture. Irrigation also made large areas of new land cultivable.

The Tigris and Euphrates took parallel courses across the Mesopotamian plain, but at slightly different elevations. The plain was essentially flat; the rivers dropped 30 meters over a distance of 700 kilometers. Overflow channels connected the rivers during spring floods, and the first irrigation schemes exploited these channels. The land between the rivers was a mix of swamps, stands of date palms, forest, shrubs and grassland. Large herds of gazelle, along with other herbivores and their feline and canine predators, originally occupied the plain. The Euphrates carried a lot of silt; its delta moved out into the Persian Gulf at 15 miles per 1000 years, so ancient trading cities near the gulf are now 50 to 70 miles inland. Irrigation agriculture would have had all the disadvantages of rainfed agriculture: a poorer diet (with sufficient calories, but less balanced, with less protein, and less calcium, potassium, and other minerals and vitamins, and thus leading to poorer overall health, more skeletal disease and shorter stature); the diseases and parasites that come from contact with water containing human excreta (various worms, including those that cause schistosomiasis), and those that come from close contact with domestic animals (many of the latter are also crowd diseases that require a sufficient density of human population to maintain themselves and so flourish in cities); the skeletal problems caused by hard physical labor; and earlier death. But at least at first, some of these irrigation societies were rich and grew a wide variety of crops, including pulses and some vegetables and fruits (such as onions and figs, sources of sugars, minerals and vitamins). Animal protein came from herds of goats and sheep that were pastured out on the plains in summer, along the rivers in winter. Wooden rafts supported by inflatable goatskins brought commodities down the Tigris in summer. Timber from the rafts and the commodities, including semi-precious stones and copper, were sold, and the goatskins packed back upstream. The actual extent of nutritional diseases would have depended on how well food was distributed; of waterborn diseases on the city’s organization of things like water supply and sanitation (whether drinking water and human excreta were separated). That is to say, depending on the political situation (the extent to which the needs of the people were taken into account), the jump in agricultural productivity associated with irrigation agriculture might have let these peoples raise their general levels of health (as well as raise the standard of living of their elites), at least for some time.

There were the usual advantages of agricultural societies: a higher birth rate and higher population; permanent dwellings; fine and varied craft work; the development of the sciences of mathematics, engineering and astronomy; the construction of large public buildings; improved methods of war; and writing. In the several times writing has been invented (Sumeria; Mexico; perhaps Egypt; probably China; perhaps Peru) it always flowed from irrigation, or quasi-irrigation, societies. Sumerians seem to have invented writing first, part of the great head start of Eurasia in cultural evolution. This was a gift of geography and biology, as a modern writer has explained. The easily domesticated plants and animals of southwest Asia could be grown without much adaptation north and west through Europe and east through much of Asia, an immense area, which led to societies influencing each other with ideas, new crops, new inventions; thus cultural development was rapid. Writing in Sumeria began, like the knotted strings of the Inca, from the need to keep agricultural accounts. By making possible the recording of knowledge (as well as that of wealth) writing made possible the accumulation of knowledge (in mathematics, biology, astronomy, physics, law, natural history, human history); that is, it made possible the modern world.

Irrigation societies in Mesopotamia would all eventually collapse because of the character of the landscape’s soils and the climate. Failure through saltation, accumulation of toxic minerals, or waterlogging is the fate of virtually all large-scale irrigation schemes in hot, dry climates. The muddy waters of the Tigris and Euphrates had a relatively high salt content. This was partly natural, partly the result of some thousands of years of agricultural erosion and deforestation upstream. The high summer temperatures of the Mesopotamian Plain meant a high rate of evaporation and of water use. The time of spring high water meant that crops, unlike the rainfed grains of the Mediterranean uplands or those in Egypt, where the Nile flood arrived in early autumn, allowing for a late autumn sowing, were grown in the summer heat. Thus they required a lot of water. The high salt content of the water and the relatively impermeable soils meant that the soils would inevitably begin to accumulate salt. Salt interferes with the ability of plants to take up water and thus reduces their growth. This soon became apparent and new land was brought into cultivation as the fertility of the old fields fell. (Modern irrigation schemes in impermeable soils sometimes solve this problem by installing drains to carry away the excess water.) The development of new lands maintained total agricultural productivity and accomodated the rising population for a long time. But the climatic drying that began 5800 years ago continued. As new land ran out, and population pressure prevented the use of long-term fallows, crops in Sumeria shifted from wheat to the more salt-tolerant barley. The cities also needed wood, which had to be within an economical hauling distance (some came down the Tigris in rafts), to smelt metal, fire pottery, brew beer, burn brick, cook the pulses and grains, and for building material. Deforestation added to the salts and silt carried by the river water. The irrigators kept cows, pigs, chickens, and goats, and so the cutover forests were grazed, which prevented their regrowth. Such use slowly transformed the whole landscape within the reach of the Sumerian cities and intensified the load of silts and salts that fed the rivers. Rising silt loads made keeping the canals open a constant problem, and sent the Euphrates migrating across its plain. Such problems take time to develop on a large scale, but unless dealt with, become (like our rising curve of carbon dioxide) more and more inexorable in their effects. About 5500 years ago equal amounts of wheat and barley were grown in Sumeria, by 4500 years ago wheat amounted to 15% of the crop, by 4100 years ago 2%, by 3700 years ago no wheat was grown. Crop yields remained high until 4400 years ago —that is, for 1100 years, far longer than we have been growing industrial grain in the American Middle West. After 4400 years ago, no new land was available and crop yields fell by 40% over the next 300 years. From 4200 to 3900 years ago there was a region-wide drought. Egypt’s Old Kingdom collapsed about 4200 years ago. Water levels in the Euphrates may have fallen below the beds of the canals. The drought was so severe that in fields near the Syrian border the earthworms died. The first external conquest of the region occurred almost concurrently with the end of new land, 4375 years ago. By 3800 years ago yields were less than 20% those of earlier times and the society had effectively collapsed.

Sumerian agriculture might have been sustainable if it had been handled differently, using fields over a long rotation (like the Hohokum of the American Southwest). Some ancient irrigation agricultures were sustainable: Egypt’s; the Mayas’ ditched swamps; the raised beds of the Tiahuanaco; paddy rice in Asia; floodplain agriculture along the lower Mississippi or Amazon. None of these are irrigation agricultures in the classic sense. In the Nile Valley the flood was usually high enough, and the soils beneath were more permeable, so the water washed the salts from the flooded land. Agriculture along the Nile was a sort of improved floodplain agriculture, much like that along the Mississippi and the Amazon. In the swamps of the Maya and the raised fields of Tiahuanaco, the water percolated up from below. Paddy rice involves a constant slow flow over a more or less impenetrable substrate.

Until the building of the dam at Aswan, Egypt’s Nile Valley was probably the most naturally productive agricultural landscape in the world. When invaded by Napolean in the 1790s, Egypt’s wheat yields were twice those of France. By then the valley had been cultivated continuously for 7000 years. Half or more of Egypt’s cultivable land is in the delta. The geology of the lower Nile Valley and the use of its natural overflow basins for agriculture removed the problems of saltation and waterlogging. After the flood, the water table would drop 10 feet below the valley bottom, letting the flood waters drain away. The timing of the overflow also helped. Water from the spring rains in the uplands of east Africa (present-day Ethiopia and Uganda) reached the Nile Delta in September, so crops were sown in late fall and matured in the cooler temperatures of winter. Spring and summer irrigation was restricted by the available technology to areas near the river, which the floods would leach clean of salts every year. Fertility was provided annually by the silt, and also by human and animal manure. Fertilising minerals came with the river water from the highlands of Abyssinia, humus from the jungles of central Africa. As in Mesopotamia, the volume of silt may have been increased by deforestation for agriculture in Ethiopia and for metal smelting in the Ugandan uplands. But the river was also cleaned and regulated by its passage through the swamps of Nubia, before it fell to the lower valley. The Nile also provided fish, both in the river and off the delta. The nutrients and fresh water brought down by the Nile supported fisheries throughout the eastern Mediterranean. The problem with the Nile flood was its unpredictability. Low floods occurred about twice a decade. The heights of Nile floods are connected to El Nino Events, which influence the northward reach of the Indian Ocean monsoon, and thus the extent of spring rains in Ethiopia. Two low floods in a row were a disaster. A flood can also be too great, remaining on the land too long and preventing the sowing of the winter crops. So, loosely speaking, the agricultural area would have supported a population that could store sufficient grain for 2 years. But population control is not the point of high civilisations, the timing of low or high floods wasn’t predictable, and since Early Dynastic times the population kept rising above the food supply. Periodic starvation was common. Of course over such a long period of time Egypt also had more severe climatic disasters. The end of the Old Kingdom was caused by 300 years of low floods. A drought in the eastern Mediterranean 3200 years ago stressed all the civilizations of the area. It helped in the collapse of Mycenaen Crete, already half-destroyed by a tsunami from the volcanic eruption on Santorini. The earthquakes that accompanied the eruption apparently compromised the island’s aquifers. The Cretans traded olive oil and wine for grain from the mainland; they also grew some wheat themselves; the drought reduced their crops and meant less grain was available from the mainland. Even in this lucky landscape, the Egyptians were caught between the constant increase in the human population and the behavior of the river.

Paddy rice constitutes another sustainable agricultural system. Tropical soils in humid climates, once cleared of their natural vegetation, are in general impervious and nutrient poor. The soils are old, and have been depleted by rainfall, plant respiration, and internal erosion. Most of their nutrients are concentrated in the vegetation that is removed. In paddy rice cultivation, the nitrogen that feeds the rice plant comes largely from blue-green algae that colonize the warm, slowly moving water that covers the paddy. The water itself, descending from the uplands, provides some nutrients (phosphorus and other minerals). Trampling and working of the paddy bottom makes the soil more or less watertight, so water and nutrients are retained. Fish and freshwater invertebrates grow in the paddies and the feeder canals. In the Lake Biwa basin of Japan, very old paddy fields are used by the lake’s catfish as a spawning area and nursery: that is, as an extension of the lake itself. This use is a benefit both to the farmers, who harvest some of the fish and whose rice is more productive, and to the fish. In some cases the nutrient-rich overflow from the paddies is led to duck ponds, whose algal and insect life (food for the ducks) is supplemented by grain. The ponds, their bottom muds fertilized by the algal and bacterial growth and by that cycled through the ducks, are periodically drained and planted to vegetables. Fertility of the paddies is also maintained by adding manure from the animals that plow them, human manure, ashes, the walls of demolished mud-brick houses impregnated with soot and grease from cooking.

The water buffalo whose manure ends up on the paddy and increases its yield of rice, is fed from forage cut in the nearby forest. Irrigation water also comes from the forest. So the forest is part of the paddy system. It also provides firewood, small game, material for building and basketry. Lowland rice-growing systems, irrigated by large rivers, also depend on a predictable supply of good quality water. These systems can be overwhelmed by timber cutting in the watershed and the change in the quality, timing and amount of water delivered to the paddies that this causes.

So some agricultural systems of “high” civilizations were sustainable, some not; some landscapes could stand more human development, some less. Any human civilization is a outgrowth of an existing landscape and climate, that is, of levels of rainfall and temperature, of sea levels, flood levels, the likelihood of extreme weather events. All agricultural systems can be pushed over the edge by too much development about them or by small climatic changes. Increase in population is often the problem, though technology also matters, in that technology magnifies the effects of population. In the 1800s, perennial irrigation to grow cotton (three crops a year) began to salinize Egyptian fields. The building of the dam at Aswan, which cut off the natural flow of water and silt, turned the Nile Valley into an unsustainable agricultural system. Salinization is now a problem, the fishery for sardines off the delta has collapsed, and without a yearly influx of silt, the land in the delta is receding.

The Natural History of the Present, Chapter 8

Chapter 8: What was Wrong with the Edible Landscape? Why Agriculture?

The reasons for the adoption of agriculture are a mystery. A writer has summed up the effects of agriculture on human populations as malnutrition, periodic starvation, epidemic diseases and class division; he might have also included ‘civilization.’ Population pressure is the usual explanation. In most parts of the world horticulture closely followed the extinction of the Pleistocene large mammals. (Some people found other solutions to decreasing supplies of wild foods or expanding human populations. The Hawaiians—also horticulturalists—fattened mullet in tidal pools, while the Aborigines of southeastern Australia built weirs that created vast seasonal swamps for the production of eels. The eels were traded.) Animal herding is supposed to have preceded agriculture, but grains were being grown 12,000 years ago in the Near East, 1500 years before the usual dates given for the domestication of sheep. Signs of domestication are not always easy to read and the herding of semi-domesticated sheep and goats, as the Lapps and the Siberian tribes herd reindeer, may have preceded all this, while the first domesticated plant may have been figs. The large mammal extinctions coincided with rising seas and a warming and drying climate. Rising sea levels flooded continental shelves and ocean banks. Some of these habitats, such as the steppe connecting Alaska and Siberia, and the continental shelves off the north European coast, were very large. Animals and people were driven inland. The warming climate dried up the grassy Saharan savannahs and their rivers with crocodiles and hippopotami. It stranded a population of African elephants along the North African coast. This population of animals declined as the climate dried further and were hunted for ivory. The last of them may have become Hannibal’s elephants, led over the Alps to Rome. Such changes in climate reduced human habitat. The shifting climate resulted in deciduous forest covering much of temperate Asia, Europe and eastern North America. Much of this landscape had been steppe, or shrubby grassland with clumps of trees, inhabited by herds of horses, bison, elephants and reindeer, and by bands of human hunters. Productivity in the oceans, and in tropical forests, both limited by a lack of iron, shifted, as changes in atmospheric circulation patterns meant new winds carried iron-rich dusts from newly dry environments to new places. Expansion and contraction of the Amazon rainforest is thought to be partly caused by the supply of Saharan dust. Changes that cause a northern movement of the Intertropical Convergence Zone bring the summer monsoon from the Indian Ocean north and increase rainfall in the Sahara Desert; southward movement dries the desert. Very small changes in rainfall make the desert expand or contract. The Sahara was very dry during the late Ice Age, about 20,000 to 15,000 years ago. The Sahara grew wetter about 11,000 years ago as the glaciers melted, then began drying about 5500 years ago. At this time the rock paintings on desert walls changed from buffalo, crocodiles and elephants to small Saharan cattle, apparently newly domesticated: perhaps domesticated because of the growing drought.

So agriculture began during a time of rapid climate change. It didn’t begin in the Middle East. It began worldwide, about 10,000 years ago, with people growing plants in many different places. We Westerners, living in an era of unlimited fossil fuels, and with an extremely progressive view of history (a product of our material lives), see no mystery in this. Agriculture pointed the way out of the cave. Agriculture gave people more apparent control over their environment, through a more intensive manipulation of it, and thus more control over their lives; it made possible a sedentary life with permanent dwellings, easily storable foods, tools, clothes, beer, cooking utensils, decorative objects; more children. Agriculture can support many more people than hunting and gathering. Modern calculations indicate that solar-powered agriculture, with field work performed by men and animals, can support 64 to 256 people per square kilometer; in warmer, wetter climates multicropping is possible and the potential population doubles. Gathering and hunting can support up to 4 people per square kilometer (this is a low estimate). The worldwide average density of hunter-gathers is 1 person per 26 square kilometers (about 0.04 people per square kilometer). Most hunter-gatherers live at 20-60% of the calculated maximum carrying capacity of their environments; this may indicate their environments’ actual ability to provide continual subsistence. Similarly, wolves in Yellowstone keep elk at 20-30% below what the weather, through its effect on vegetation, would support; and thus create a more stable elk population.

With dense populations of sedentary agriculturalists, the arts bloomed: pottery-making, metal-working, tile-making, wall decoration. Many of these arts were heavy users of fuel. Mathematics, architecture, astronomy, and writing advanced along with larger, more complex, and more hierarchical societies; societies with hereditary classes of rulers, priests, warriors, artisans, farmers. Growing agricultural surpluses, that is, more excess production per farmer (as in Egypt, where a peasant produced five times the food required by his family), made possible the support of the non-farming classes. War was a sort of investment policy; a means of adding to the city’s wealth. War brought wealth through tribute and booty: in most premodern societies it is thought wealth came more from either increasing a group’s lands or war than from technological innovation. Behind all this was population growth. One of the effects of settled life is more frequent childbirth. A mother who moves camp every few days or weeks cannot deal with more than one non-ambulatory child. Some anthropologists think that nursing, which helps inhibit ovulation, went on for 4 to 6 years in a normal, that is, a gathering and hunting, society. (Gathering and hunting is by far the longest human adaptation.) At any rate, births tended to be spaced every 4 to 6 years. In an agricultural population births are limited mostly by the food supply and tend to come every 2 years. So populations began to rise. And as long as people were willing to work more, and more land was available, as long as the rains came, or the rivers rose and fell in a predictable way, agriculture would continue to feed many more people (ten to a hundred times more) per unit of land. In Neolithic Europe an agriculture of cattle, goats and hoe-cultivated wheat is thought to have supported 1 person per 120 hectares (50 acres), or about 8 per square kilometer (13 per square mile), twice that of the acorns and salmon of northern California. Most of the land was needed for browse for the animals. In Mesopotamia, cultivated land supported 100 or more people per square kilometer. (The population may have reached 20 million, with two-thirds of its 35,000 square miles of arable land irrigated, before the collapse.) A larger population is always the aim of biological evolution, and in human society, as in wolf society, numbers matter: the larger group wins the competition for resources. More resources allow the population to grow further. (Of course, technology can compound this.) Some anthropologists think the advantage of being able to mobilize people for war explains the development of agricultural chiefdoms and early states.

But none of this would have been apparent to people who harvested a few baskets of wild wheat, spilling some as they cut it down and carried it home (thus fulfilling the dispersal strategy of the wheat plant); or planted a hill of gourds (useful as containers) at a campsite to which they were likely to return in three months. Gathered wild grains may have been special foods at first, used for feasts, or to make beer. (Fruit-eating animals like elephants, American robins and people have a long acquaintance with fermentation, which is one way fruits attract attention—and explains those robins flying into autumn windows—but standard histories put the fermentation of beer several thousand years after the cultivation of grains.) The advantages of agriculture come at a later stage when people have, voluntarily or not, gathered into villages, when populations are denser, and agriculture is providing 90% or more of dietary calories. With the advantages of agriculture comes a down side: starvation, disease, more hierarchical societies, poorer health. The poorer diet, mostly of grains, expresses itself in shorter stature (the height of men may have fallen 6 inches, of women 5); in nutritional diseases like anemia and osteoporosis; in vitamin deficiencies; in overall poor health. Death comes earlier than among many of the gatherers, perhaps at 19 years in early agricultural societies, compared with 26 in groups of hunter-gatherers. (Such figures are disputed and vary. Cistercian monks in the 1300s died at an average age of 35, but it isn’t clear this figure takes into account a childhood mortality of 25-30%.) The heavy manual labor of agriculture causes degenerative skeletal diseases. Infectious diseases become more of a problem, partly because of the crowding, partly because of close contact with domestic animals, who are reservoirs of diseases that directly infect or adapt to humans. About 50 diseases are shared with cattle (including smallpox, measles, tuberculosis, and diptheria), 65 with dogs (our oldest companion), 46 with sheep and goats, 42 with pigs (including flu), some with birds (other flus), a few with horses (perhaps the common cold). Drinking water contaminated with human wastes spreads cholera, dysentery, and intestinal parasites. The parasitical diseases schistosomiasis and malaria are associated with irrigation in warm climates.

One scenario for the development of agriculture in the Middle East involves the Natufian people of present-day Israel and Jordan. About 15,000 years ago the Natufians lived on wild acorns and pistacios and hunted gazelles and wild sheep, in a landscape managed by burning. Their permanent villages were made possible by the abundant acorn crop, itself a consequence of more rainfall in the eastern Mediterranean with the retreat of the glaciers north. They also collected wild grains (wheat and two kinds of rye); these large-seeded grains returned a lot of food energy for the effort exerted in their harvest. The shutting down of the Gulf Stream between 13,500 and 12,600 years ago during the Younger Dryas Event (the result of the draining of a glacial lake in the center of North America into the Labrador Sea), caused temperatures to fall in northern Europe and a thousand year drought in southwest Asia. The acorn and pistachio crops collapsed. The Natufians, already living in villages, began cultivating cereals and keeping domestic animals. Large-seeded annual grasses such as wheat, emmer wheat and rye already formed large natural stands in their area. (In the 1960s, botanists found wild grains growing in more or less pure stands over hundreds of hectares in the same area.) The domestication of grains like wheat involves selection for plants that don’t drop their seeds when harvested, and whose seeds will sprout simultaneously when planted. It is thought the domestication of emmer wheat would have been rapid, taking 20 to 100 years, not several thousand, as with maize. (Emmer wheat is a natural hybrid of two grasses that occurred in the Near East 30,000 years ago. Bread wheat is a hybrid of emmer wheat with another grass that occurred 10,000 years later, at least 8,000 years before bread wheat was cultivated.) When warming resumed in Europe and rainfall improved in the eastern Mediterranean, farming and the keeping of domestic animals had taken hold; the villages had become larger. A later drying of the climate in the Near East, which made the growing of rainfed winter grains difficult, is thought to have led to the development of irrigation agriculture.

At some point an agricultural population outgrows its supply of wild game and gathered foods. Then return to an earlier way of life is not possible. (When their populations were still small and harvests were bad, the Anasazi, like the Pueblo people that survived them, made up the difference with wild grass seeds and pinion nuts; later, their population was too large and their landscape too altered for such foods to help.) In general, as populations grow, domestic animals, kept for meat, milk, fat, hides and traction power, are pastured on the stubble fields and in the surrounding wasteland, increasing the pressure on the local environment. Crafts such as pottery and metal-working require fuel, buildings need timber, grains must be cooked, and so trees become scarce and distant. Grazing prevents the re-establishment of forests cut for timber and fuel. As forests disappear, small streams dry up, floods increase, the land erodes, rivers grow more salty. Farmlands yield less, under continuous crops of grain. Crops also sometimes fail, and as the population grows, the threat of starvation becomes more constant. Unforseen or unmanagable environmental problems appear, sometimes the consequence of greater environmental manipulation, sometimes the result of natural disasters or of natural shifts in climate. Populations near the carrying capacity of their environments make collapse of the civilization more likely. Past problems include soil erosion about the Mediterranean basin and in upland Mesopotamia; too great or too low floods in Egypt; the slow saltation of irrigated lands in lowland Mesopotamia (these lands, like those in the American Southwest, require a long fallow to avoid saltation and waterlogging); droughts in the Andes, and in the Mayan highlands; a tectonically mediated rise in the water table along the lower Indus River that flooded the foundations of the city of Mohenjo-Daro, and required the firing of more and more brick to build the buildings up, with more and more wood cut from the drying jungle; the “dry fog” in 535 AD (from a volcanic eruption? an exploding comet?) that cooled the climate and caused crop failure and famine in Europe, southwest Asia and China. Trade, perhaps allied with weather conditions, such as the warm, wet spring weather that increases the presence of bubonic plague in the marmots of the Asian steppe, introduces new diseases, to which populations are not adapted. Rome suffered from several plagues in the years after 144 AD, at a time when a warmer, dryer climate in the southern and eastern Mediterranean and in North Africa was disrupting its agricultural base. By then the conquests that had made the early empire wealthy no longer paid their costs. (The lightly settled northern lands lacked the wealth of the older Mediterranean cultures that were first taken over.) From the first century on, the tax base of the empire was largely agricultural. Taxes, though heavy, fell short of paying the costs of administration and defense became more and more difficult. The population never recovered from the plagues of the second century. The plague of Justinian that started in 542 AD may have killed half the people in the empire. In an overpopulated society disasters and epidemics could be an economic blessing. The Black Death, which is thought to have killed a third to a half of the population of Europe from 1347-1349, was followed by a century of recurrent epidemics of diseases with severe mortalities (plague, smallpox, flu, dysentery), along with some episodes of starvation, so that in 1450 the population of Europe was probably half that of 1347. (Without the additional epidemics, the population would have recovered in 30 years. The population of China, which was affected by the Black Death earlier, also fell by half from 1200 to 1400.) The depopulation of Europe gave a considerable push to the economic expansion of the Renaissance. Poor farmland was abandoned, so crop yields rose. Food became more abundant, labor scarcer, wages higher (50% higher in Florence, compared with 50 years before); the poor gained wealth and bargaining power, which led to the peasant revolts of the late 1300s and the gradual erosion of serfdom. Technological innovation grew. Much wealth was transferred from the dying, some of it to the new European universities. In England, land without heirs went to the local nobility, who grew richer, and also financed development schemes, such as mines and the reclamation of waste land for agriculture. In general, the landed gentry lost wealth and power compared to the laboring classes. Depopulation resulted in a more diversified, more capital intensive, more technologically advanced economy, and a more prosperous population.

The Natural History of the Present, Chapter 7

Chapter 7: Limits of Sustainability in the More or Less Edible Landscape; Varieties of Desert Agriculture

Some landscapes, like the northern European hardwood forests, or the humid prairies of North America, are more tolerant of human agricultural occupation; some are less so. (Both the former are part of the loess belts of thick, wind-deposited glacial silts, which make excellent, if easily erodible, agricultural soils.) Limits often appear more dramatically in arid landscapes. The Papago Indians (the so-called bean eaters: their proper name is the Tohono O’odham) inhabited the Sonoran Desert of Arizona and northern Mexico. They were flood-water farmers; or partly so: it is thought 20-25% of their calories came from cultivated foods. Among the 75% of their diet that came from hunted and gathered foods, 4 times as many calories came from plants as from animals. The Papago farmed the mouths of desert washes, where the flood waters from the July rains spread out. Low embankments, shallow ditches and brush weirs were used to divert and distribute the flow. A brush weir constructed across the flat slowed the rush of water, made it spread out and drop its load of leaves, small sticks, rodent droppings (all excellent fertiliser); slowing its flow helped the water sink into the ground. Corn, squash, beans and pumpkins were seeded in the damp ground. Fields used for many years developed their own associations of wild plants. Some of these were allowed to seed in and were in a sense cultivated. (So-called cultivated devil’s claw, a plant used for basketry, may have been among them, as was goosefoot, a weed harvested for greens; and cross-pollination with wild chilis growing around the edge of the garden added heat to next year’s planted chilis.) To mature well, the crops usually needed a second and even a third watering. This was provided by the later, gentler, female rains, though tepary beans needed less water than corn, and corn less than pumpkins. Yuma corn, grown on the floodplain of the Colorado River to the west, matured in 60 days in ground left saturated by the receding floodwaters. So this was a system dependent on natural regularity, in a very variable environment; that is, the amount of rain and its timing varied from year to year. The environment’s variability helps explain the low level of the Papago’s dependence on cultivated foods.

In all ways water is the desert dwellers’ problem. The Papago dug shallow reservoirs near their fields to catch additional run-off (which they might use for hand irrigation as well as for household water) and also dug wells in the beds of washes. These usually held water until October or November. By then the crops had been harvested, the agricultural year was over, and the deer dance was performed to mark the start of the winter season. The tribe moved from the drier mid-altitudes where its fields were located and where the desert fruits, the foods of spring and summer, grew, to its higher, better-watered perennial grasslands: the animal pastures. Flood-water fields were partly created; they might be leveled with earth dug from the reservoirs, and enriched with nitrogen-rich earth collected under mesquite trees or other nitrogen-fixing desert shrubs, and carried in baskets to the site. Their layers of silt were increased by the brush dams. The settling silt helped level them and also made them fertile; the yearly flood of silt and organic matter renewed the fertility. Older fields had over a hundred characteristic plants, besides crop plants, and a rich insect and invertebrate life. They attracted a more varied and concentrated collection of mammals, birds, reptiles and amphibians than the surrounding desert. The man-made concentration of water and nutrients turned the fields into little oases; such fields became centers of local biological diversity. (One hundred and ten species of birds are found about Papago fields). Some of this life, especially the competitors for the crops, like rabbits, would be eaten.

Many of the collected foods of the Papago were strongly seasonal; abundant for two weeks or a month, and then gone. Such foods included the fruit of the Sahuaro and Organ-pipe cactus, which ripened in June; cholla buds and fruit; mesquite beans (mesquite yields something like 150 pounds of pods per acre, and the beans don’t require cooking to be edible); the seeds of ironweed and paloverde, and of several desert grasses, out of which a nutrituous mush was made, higher in protein and fat than cooked wheat; various greens; and sandfood (a parasitic fungus that grows on the roots of a desert shrub). A family might also consume 12 to 15 black-tailed deer per hunter, as well as other game. If these figures are accurate, it puts Papago meat consumption from large animals far above that of Northeastern tribes like the Iroquois, whose take of deer and bear in the winter hunt is estimated at 40 pounds of dressed meat per person, or less than one animal each. (The Creeks of the Southeast reportedly used 25 to 30 deer per household annually for meat and skins; in the 1700s during the trade in deerskins for European goods, Creek hunters killed 100 deer per household per year.) With these numbers, each member of a family of 5 Papago is consuming 2 to 3 deer. The desert also provided black-tailed jackrabbits, an animal of cyclical, sometimes enormous abundance, which the Pueblo Indians killed in drives; white-tailed deer; desert bighorned sheep; Merriam’s elk (now extinct); pronghorn antelope; doves and quail and their eggs; and wild turkeys. Grasshoppers were gathered for a protein-rich mush, and the larvae of the lined sphinx moth, extremely abundant after the summer rains, were dried and stored.

The neighbors of the Papago, the Pima (Akimel O’odham), who lived along the Gila, were floodplain irrigators. Where the Pima lived, the Gila floodplain was four miles wide, much of it floodplain forest. The oval fields of the Pima were surrounded by planted hedgerows of mesquite, willow and aspen. Sticks were woven among the trunks; the fence helped slow and control the irrigation waters. Mesquite was common on the floodplain, and its beans were harvested for food. Pima canals were up to 10 feet deep and 4 to 6 feet wide. The water was forced into the canals by diversion dams. Pima crops would mature with one heavy, pre-planting irrigation. The muddy floodwaters, a product of the winter’s snowmelt, also fertilised and helped level the fields. The spring flood of the Gila was caused by mountain snows, which were more reliable than summer rains, but would fail once every 5 years. Additional irrigation during the growing season produced more abundant crops and the Pima also constructed temporary embankments and dikes on the flats beyond the floodplain to divert sheet and arroyo runoff from the summer rains onto their fields. Such structures may have helped them garden in years when the spring flood failed. It is thought the Pima got 50-60% of their calories from cultivated crops. Their additional manipulations of the landscape somewhat reduced their dependence on climate variability. Instead of being dependent on a cloudburst flooding the drainage of a wash, they were dependent on a season’s snowfall over a large mountain drainage, and, to a lesser extent, on the summer rains that fed their other water traps. Since they cast a wider net, the likelihood of failure was reduced, and they could be more dependent on agriculture. In a good year the Pima could grow 2 crops (one with the spring flood, one with the July rains), and so have harvests in both July and October. Many of the Pima’s other foods (such as cactus fruit and mesquite beans) were similar to those of the Papago. In bad years they ate more collected foods. For this reason they may have encouraged the growth of mesquite trees on the floodplain. They also ate fish. Before Euro-American settlement, the Gila, like many southwestern rivers, was a slow-flowing, low-banked river, with canopy forests of cottonwood, willow, mesquite and walnut, grassy meadows, and rich marshlands with waterfowl and amphibians (the cienagas). Fish from the Gila were a staple (the Spanish claimed the Pima supplemented their diet of fish with corn and beans), especially the humpbacked sucker, which was netted in commercial quantities from the Salt River until the 1940s. (The humpbacked sucker is now extinct in the Gila. Fish were also important for the tribes along the lower Colorado.) Beaver were eaten. Beaver were plentiful along the tributaries of the Gila until trapped out by the Americans, another indication that much or most of the near-river floodplain remained densely wooded.

Like many New World tribes, the Pima practised no soil fertilization, except through the yearly flows of muddy water. As I have pointed out, North America had no large domesticable wild animals, whose domestication would encourage the use of pasture crops, which could be rotated with grain, and whose fertilising manure could be spread on the fields. A Hidatsa woman, whose people gardened in the Missouri floodplain in the mid-nineteenth century, remembered carrying horse droppings out of her gardens: they were a source of weeds. Pima soils remained productive, though it was said new land produced better, and the wheat and barley introduced by the Spanish, and adopted by the Pima as winter crops, tended to be soil-depleting. The three main native crops (the Pima also grew cotton and tobacco, both notoriously hard on soils) were corn, beans and squash, planted together in the same field. Up to a point, these were soil maintaining. Corn, the soil-depleting crop, formed a standard for the climbing, and nitrogen-fixing, beans; squash, another nitrogen user, spread its trailing vines with their large leaves out between the corn hills and sheltered the ground from sun and erosive rain. Where floodwaters did not fertilize the ground, as with the light upland soils favored by Native Americans in New England, New York State, and southern Canada, fields were only cultivated for 10 years or so, then the field, and often the village, moved. Free-living, nitrogen-fixing bacteria will provide a yearly pulse of nitrogen to continuously cultivated fields, but growing cultivated crops year after year, without a rotation into sod or forest (the poplar plantations among the cornfields of Italy and France, the plantations of pine pulpwood on the Minnesota prairie), tremendously slows the mobilization of nutrients from the soil. So productivity falls, to a low, constant level. The fields of the Narragansetts of Rhode Island were unusual in that they were apparently capable of bearing continuous crops of corn, though some accounts indicate the fields were left fallow in alternate years. (There is now doubt that the New England Indians used spring-run herring for fertiliser: it has been suggested that the use of fish was an English innovation; one writer pointed out that the Narragansetts would have been better off eating the fish.)

Landscapes like those of the Pima are easily over-exploited. All rivers are subject to cycles of downcutting and channel migration, as their floodplains, built up by layers of springtime silt, mature and grow above the reach of the spreading floodwaters. This cycle is more rapid in the young, rapidly eroding landscape of the American Southwest. For some combination of reasons (a decrease in vegetation, perhaps from drought; an increase in rainfall; tree cutting or grazing that lets storms produce more runoff and more silt) a flood begins cutting a deeper channel. This leaves the old floodplain out of reach of the floodwaters. More water is confined to the channel, which increases its erosive power. The deepening channel migrates inexorably upstream, sometimes dramatically so, in the form of a receding waterfall. Floods on the Colorado River in 1905 and 1906 led to its taking over an irrigation canal leading to the Salton Sea, a natural depression in the desert, as its main channel. According to Indian legends, this was not the first time the river abandoned its delta in the Gulf of California. The rush of water created a headwall recession in the form of a waterfall 40 to 80 feet high and 1000 feet wide, that receded upstream at a rate of several thousand feet a day. People came out from Los Angeles to see it. After an episode of downcutting, parts of the old floodplain are undercut and washed away by the river, which finally adopts a shallow and braided (rather than a deep, single) channel. Trees, or other perennial vegetation, which might stabilize the channel, have trouble establishing themselves because of the annual floods. Few fish survive in the shallow, warmer water and beaver cannot colonize the river, and help stabilize it with their dams, without trees. In time, given a sequence of favorable events (two or three good years for aspen seedling survival, for instance; or colonization by the invasive tamarisk), a single channel will form again, and a floodplain reform.

Something like this seems to have happened to Chaco Canyon in north-central New Mexico in the 1100s. The canyon had been occupied by the Anasazi people for 600 years and was densely settled. Wide ceremonial highways connected massive public buildings, and carefully laid out roads, for transporting pottery and grain in backpacks, connected Chaco with other Anasazi settlements. The Anasazi of Chaco were a state trading culture, exchanging pottery and other goods for grain among their various settlements. Thus they redistributed grain in a region of variable climate. The Chaco River was a shallow seasonal stream with a floodplain several hundred feet wide. Chaco Canyon caught runoff from a wide area and had a high rate of soil renewal and a high alluvial water table. Its relatively low elevation gave it a long growing season. The early Anasazi grew crops in the damp alluvial soils and diverted sheet runoff over the canyon bottom into irrigation channels for further irrigation. They hunted deer and collected wild grass seeds. Later they also grew crops on the mesa tops, under a mulch of stones. The stone mulch broke the force of a hard rain, letting water seep in; reduced evaporative losses from the soil; reduced erosion; reduced the temperature variation between day and night; and condensed dew. (In modern reconstructions, rock-mulched soils have double the soil moisture and four times the average yield of unmulched soils. Rock-mulched gardens were especially common in the Southwest during the droughts of the 1200s and 1300s.) The nearby watershed of the canyon, including the mesa tops, was originally occupied by a pinion-juniper woodland. The Anasazi collected pinion nuts for food and cut the trees for building material and for fuel for cooking and firing pottery. Regrowth is slow in the Southwest and as the population grew, the nut and deer harvest declined, people ate more rabbits and mice, as well as domestic turkeys raised on corn, and cutting overtook the rate of regrowth. Southwestern pinyon-juniper woodlands are a mix of bare ground, grasses and trees. Approximately 20% canopy cover by the trees constitutes dominance (the roots go into the openings and compete with grasses for moisture); herbaceous cover amounts to 15-20%; the rest is bare ground. When too many trees are removed by cutting, or when the forest occupies too much of the ground because of fire suppression, or when the grasses are overgrazed by cattle or sheep, the patches of bare ground connect and erosion is inevitable; net soil loss has been measured at 0.5 inch per decade, or 5 inches per century. While the stone mulches on their upland gardens should have prevented erosion, erosion probably explains why little now grows on the mesas about Chaco.

The buildings of Chaco Canyon also took tens of thousands of ponderosa pine timbers, carried from up to 30 miles away. In the century that preceded abandonment, 75,000 to 100,000 large pines may have been cut in the Chaco River’s watershed (some writers say 200,000 trees; not a lot of trees, really, for a population of some tens of thousands of people over a century). Trading pottery (and to a lesser extent worked turquoise) for grain let the Anasazi maintain large populations in an uncertain climate. Agricultural settlements surrounded the canyon. Land yielded less and less under continuous corn and new fields were constantly opened up; rainfall also varied from place to place and year to year. Trade was a means of redistributing grain, and thus of evening out agricultural production over a large area. Grain distribution was controlled by the people in the Big House, and depended on a ready source of fuel to manufacture pottery. The Anasazi elite were about two inches taller than the farmers who lived in more simple dwellings, whose teeth show signs of episodic starvation. By 1000 AD the pinion-juniper woodland was gone. (It has not regrown 1000 years later.) The main flourishing of the Chaco people occurred from 950 to 1150, during a period of high rainfall. About 900 AD the irrigation channels on the canyon floor began to downcut below the level of the fields. Clearing of vegetation, in this case the pinion-juniper woodland as well as the upland Ponderosa forests, increases the speed and amount of overland flow from rainfall. Downcutting could have begun with a heavy rain; or with a drought, which would further reduce the vegetation about the canyon, followed by lighter than normal rainfall. Under these conditions a light rain would produce heavier then normal runoff. But rain was relatively abundant and to compensate for the downcutting, the Anasazi dammed streams in the side canyons and used the stored water for irrigation. They also captured the water that came off the cliff on the north side of the canyon and built rock dams across the river itself, to raise its level. The population of the canyon remained high until a long-term drought began about 1140 AD. By then, the population in the canyon had been a net importer of corn for 200 years. A more general drought meant crops would fail all over the area and the trading system would have too little grain to distribute. Corn can be stored for 2 to 3 years, but no culture stores more than 2 years of grain. (Thus the saying that 3 years of drought kills everyone.) The natural foods of the area (the nuts, animals, wild grasses) were no longer sufficient to feed the population and were reduced by the drought. The Anasazi at this time (like the Maya at a time of high population) showed signs of nutritional stress from their restricted diets: severe dental caries, tooth erosion from the stone grit in cornmeal, periodontal disease, arthritic diseases, osteoporosis. Child mortality among the elite was 9.5%, among the farmers 26-45%. The earlier diet of corn, beans and squash had been supplemented by significant amounts of wild game and wild plant foods but such a diet was only possible when population densities were relatively low. Some of the people of the canyon dispersed to areas of higher elevation, which have more rain, but a worse drought late in the 1200s would destroy the Anasazi as a culture. Imports of food, and of luxury items such as pottery, stone, turquoise, macaws, shell jewelry and copper bells, into Chaco Canyon continued until near the end, which was rather sudden. Six hundred years later, in 1849, Chaco stream was clear and continuous with no signs of gullying. By 1871 the stream had cut an arroyo 16 feet deep and 40 to 60 feet wide; by 1930 the arroyo was 25 to 30 feet deep and 300 feet wide and the stream had become intermittent. Once it begins, downcutting is irreversible. Heavy machinery can be used to stabilize braided floodplains, although at considerable expense (hundreds of thousands of dollars per mile).

At European contact, many Southwestern rivers flowed through wide floodplains with meadows, cottonwoods, willows and emergent marshes. The floodwaters distributed seeds, soil, organic matter and other nutrients; their slow recession let cottonwoods and other trees germinate (the seedlings’ roots followed the water down). Throughout the Southwest and Great Basin, beaver, with their frequent dams on smaller watercourses, and their maintainance of a dense riparian forest of poplar and willow, are thought to have been a major factor in maintaining floodplains. The streamside vegetation slows the movement of water in floods, making it spread out and drop its fertilising sediment on the floodplain terrace. With less sediment and less water, the flow descending from the tributary streams is less erosive. The Pima ate beaver, but apparently, like the Cree, they took a limited number. The Pima also farmed only a part of the floodplain. Why is uncertain, but that is a problem only for people like us, inhabitants of a market society, for whom growth is life. The river was important to them for fish and the uncultivated floodplain for other foods. Unlike the Anasazi, they never developed a state culture that demanded a surplus for its support. Perhaps only parts of the floodplain were within reach of their irrigation techniques. Most likely, they also saw the limitations of their environment and controlled their population.

Anglo-American settlement of the Southwest (the final and by far the most environmentally demanding settlement to date) was preceded by the trapping out of the beaver. Timber, mostly mesquite, which then was restricted to river floodplains, was cut for mine timbers, building material, fuel to process ores, and for cooking and heating. Cattle were introduced from Texas. (The cattle, by depositing the seeds from the nutritious mesquite pods in fertile pats of manure, helped mesquite make its move from stream bottoms to the uplands, where its takeover of former grasslands has tormented cattlemen ever since.) A railroad in 1881 made it possible to ship cattle and cattle products, and cattle in the Arizona Territory increased from 5000 in 1870 to more than a million in 1890. The grazing pressure on the river floodplains was tremendous. The 1700s and 1800s were mostly dry in the Southwest. It was wet with floods from 1881 to 1884, then dry from the 1920s to the 1980s. A flood in 1891 altered the channels of the Salt and the Gila rivers, destroying irrigation systems and canals along the rivers. A drought from 1891 to 1893 reduced the cattle herds by half. Then a period of somewhat above normal rainfall continued the downcutting begun by the 1891 floods. Most of the major river floodplains were converted to shallow, braided channels. Streams downcut deeply. Native floodplain forests, deprived of moisture, declined, and were invaded by the deep-rooted saltcedars (Tamarix ramosissima or T. chinensis), alien plants introduced as ornamentals to the Southwest (some were planted by government crews in the 1930s to control erosion), which now cover 1.2 million acres of southwestern river bottoms. The bunch grasses of the American Southwest and Great Basin are not adapted to continuous grazing. The native herbivores, such as black-tailed deer, bighorn sheep, Merriam’s elk, and pronghorn antelope, are browsers that sometimes eat grass. Elk and sheep eat more of it, elk largely in the winter when it does no harm to the plants. While it is thought that over-grazing by cattle helped initiate the downcutting of the rivers, cycles of downcutting and floodplain aggradation are endemic in the Southwest. The area had been grazed (relatively lightly) by domestic sheep for two centuries before the Texans came. One can see the effects of the influx of cattle in the levels of sediment deposited in southwestern alpine lakes, which rose by 5 times in the middle of the nineteenth century and are still 3 to 4 times above pre-nineteenth century levels. The hooves of the cattle broke the crusts on the arid soils (crusts of lichen or wind blown gravel) and let them erode and blow away. In this case, a flood, followed by a period of light rainfall, which reduced the vegetative cover, followed by a period of heavy rain started a cycle of downcutting. Heavy grazing by cattle, tree cutting, the removal of the beaver made the downcutting more likely, more extensive, and more severe. Such practices provide more sediment, which increase the erosive power of rivers.

Much remaking of the desert landscape was deliberate. The valley of the Salt River, where the Hohokum had grown irrigated crops for 1500 years (they had been replaced about 1500 by the less state-like Pima culture) was converted into a major producer of irrigated grapefruit, dates, cotton, lettuce, melons and salt tolerant winter grains. The river was dammed to provide water. The dams dried up much of the channel and the floodplain forests (when not removed for fields) collapsed from the falling water tables. The Hohokum had dealt with the salty groundwater of the Salt Valley by rotating their fields every ten years; only 9-10,000 of the 100,000 hectares they cultivated were under cultivation at any one time. The Hohokum also grew agave on the uplands and ate fish from the river. Unlike the Anasazi, who were dispersed by drought and replaced as a culture by the less environmentally demanding Pueblo, the Hohokum seemed to deal with the environmental stresses they faced. They were probably eliminated by European diseases before actual contact with Europeans. The modern irrigators dealt with the salty groundwater by digging drains. Irrigation works along the Salt were destroyed by the floods of 1891 but were rebuilt.

Continued heavy grazing in the twentieth century has speeded up a shift in the vegetation of the Southwest from grasses to shrubs. This change in vegetation results in a change in the distribution of soil nutrients from even to patchy, as nutrients are concentrated under the shrubs. Like the downcutting of streams, this shift in vegetation seems irreversible. Why is unclear. Many desert shrubs use carbon more efficiently in photosynthesis than desert grasses. The shrubs thus need to allow less carbon dioxide to filter into their leaves from the atmosphere (through openings called stomata) and correspondingly to let less water out; so they are also more efficient users of water. A shift from plants less efficient at using carbon dioxide to plants more efficient at using carbon dioxide has been going on under limited rainfall regimes worldwide for several million years. It is probably part of the long-term adaptation of terrestrial vegetation to the tremendous decrease in the carbon dioxide content in the atmosphere since the Carboniferous, when carbon began to be locked up in fossil fuels. Since carbon dioxide uptake by plants is related to water use, drier conditions favor plants that can take in more carbon dioxide with less transpiration of water. Shrubs are also deeper rooted; the individual plant draws water from a deeper soil profile and essentially depletes the water available for any grasses growing in between them. Nutrients from fallen leaves, from fine root turnover, from small animal droppings then accumulate under the shrubs, creating the so-called patchy distribution of nutrients, and making it harder for grasses to establish themselves on the bare ground in between.

Agricultural systems like those of the Papago, Pima, and Anasazi were used in dry environments worldwide. The Nabataens of the Negev Desert of modern Israel and Jordan, whose capital, Petra, was carved out of the walls of a canyon, lived on what was 2000 years ago a caravan route from the Red Sea to the Mediterranean. From the first century BC to the third century AD the route connected India, Africa and China with Egypt and Greece through ports in Gaza, handling trade in cinnamon, cassia, myrrh, frankincense, cotton, silk and ivory. The Nabataens fed a population of 60,000 people on grain grown with run-off irrigation. Rainfall then is thought to have been very similar to that now: from 2 to 15 inches a year (that is, highly variable on an annual basis), coming in showers over a 2 week period. The Nabataens dammed some wadis (canyons) in their upper reaches and led the captured water through canals to fields below. They dammed the whole courses of other wadis with low stone dams (so-called rubble masonry, stone dams with an earth core, the dams up to 2 meters high), the crest of one dam level with the base of the next. These dams converted the wadi bottom into a series of stepped fields, that were filled with silt and partly leveled by the run-off of silt and water that flowed with the rains down the wadi floor. Crops had to mature with this single, pre-planting irrigation. The density of dams was great: near Ovdat, another ancient city of the Negev, 17,000 have been found within 50 square miles, a square a little over 7 miles on a side.

At the mouths of the wadis, natural terraces at the bottom of moderate slopes were used for another form of run-off agriculture. These fields used runoff funnelled down from the slopes above them. In modern reconstructions, the farms require about 20 acres of water catchment for 1 acre of cultivated ground. The degree of slope and the soil cover of the catchment are important. Steeper slopes tend to lose more water to rock fissures and depression storage. Moderate slopes yield about 20% of a light rainfall to the fields. The yield rises with a heavier rain. All slopes in the Negev are essentially devegetated. The system works precisely because the Negev is such a destroyed landscape (probably destroyed several thousand years before the Nabataens by people cutting wood and grazing goats, together with a slowly drying climate). The impervious soils, moderate slopes, and low rainfall lead to a rate of run-off sufficient to irrigate the terraces. In some cases, stones on the slopes of the ancient catchments have been collected into regularly spaced piles. Stone clearance increases run-off under very light rainfall regimes. (While it seems unlikely the stone piles create runoff from dew, such structures can also function as dew-catchers. Stone towers 30 feet high and 100 feet across at the base condensed water from the air to supply the ancient Crimean city of Feodosia; the average measured modern yield is 35 gallons per tower per day.)

The Negev receives about 100,000 gallons of water per acre per year. In modern times, experiments have been made with individual water catchments on the desert floor. This modern innovation involves much soil movement, but these catchments also work. The ideal size of the catchment varies with the location, but in general pomegranates will grow in 250 to 500 square meter catchments, which corresponds to a planting of 8 to 16 trees per acre (20 to 40 trees per hectare). By comparison, standard apple trees in humid regions are planted at 100 to 200 trees per acre. Grapes can be planted at 32 to 40 vines per acre (80 to 100 vines per hectare). The creation of such microcatchments also increases the density of forage plants like saltbush 20 to 30 times (they grow around the rim of the catchment and are used as forage by goats), and over time the water filtering down will clear the accumulated salts from the catchment’s soil. In such a ruined or severely altered landscape, such manipulation seems a definite improvement from a human point of view; and perhaps biologically. Catchments, colonized on their edges by forage shrubs (which help prevent soil movement), last more than a century, so the cost of construction has a long pay-off period. Regenerative agriculture in the Negev may mean encouraging the nitrogen-fixing cryptogramic crust typical of deserts (which foot traffic and bulldozing will destroy); and the rock-eating snails that are now the chief agents of soil formation in the Negev. The snails rasp into rocks to get at the lichens that grow under their surfaces; the rock comes out in the snail’s faeces converted to soil. Such biological weathering amounts to about a ton of material per hectare annually, and makes the snails critical agents in soil formation and nitrogen cycling, processes necessary for the establishment of higher plants.

Vinyards and pomegranate orchards would accumulate carbon in the soils under them, and so help remove carbon dioxide from the atmosphere. Millions of square miles of land world-wide that have been ruined by agriculture, grazing, logging, or mining, much of it dryland, including perhaps 30% of former agricultural lands, are candidates for such innovative, marginally profitable, carbon-removing schemes. Unlike modern commodity agriculture (much of it also marginally profitable), such schemes usually involve much hand work; that is, they also produce employment. One could not in modern times grow grain in the wadis of the Negev, or on the terraces of run-off farms, as the Nabataens did (the relative price of grain is now much, much lower than then) but one could grow other crops. Pomegranates or grapes in the Negev; salicornia, a halophyte that can be irrigated with seawater, whose yields are similar to alfalfa, and which makes a good livestock feed, in sea-side Middle Eastern or Indian deserts, alongside greenhouses that use cold seawater to condense moisture out of the desert air, at a gallon a day per square foot of glass (the water also cools the greenhouse, making the plants more efficient users of water); jojoba, a desert shrub whose seeds yield a useful oil, in Arizonan or Mexican fields that now grow irrigated alfalfa or cotton; Christmas trees, pulpwood or horticultural evergreens in the strip-mined hills of humid West Virginia, Pennsylvania and Ohio; deep-rooted native grasses and large herbivores underneath the towers of electricity-generating windmills, on the newly shaped, strip-mined hills of Wyoming or the Navaho Reservation in Arizona. Sunny landscapes can hold photo-voltaic collectors; or solar concentrators to make electricity from sun-heated steam. Such regenerating landscapes can be useful in many ways.