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CLIMATE AND FOOD. Throughout most of prehistory, humans acquired food by hunting, fishing, gathering, foraging, or scavenging. The animals and plants they consumed were native to the local climate and environment and provided highly variable diets. Arctic and subarctic populations fished, gathered shellfish, and hunted land and sea mammals; temperate forest populations gathered seasonal plants and hunted wildlife; prairie and savanna dwellers hunted and trapped large mammals; and tropical forest dwellers fished, gathered a variety of plant foods, and hunted small mammals. Climatic influences on the flora and fauna included in the local diet were rainfall, temperature, seasonality, and longer-term cooling and warming trends. The most extreme climate changes were the Pleistocene glacial advances and retreats in the northern hemisphere. Climatic variation in temperature and precipitation became central to food procurement when plants and animals were first domesticated about ten thousand years ago at the end of the Pleistocene epoch.

There are only a few small populations that subsist entirely on hunting and gathering of wild plants and animals, although many populations continue to supplement their diets with wild foods. An exception to this is the fish and shellfish that provide substantial amounts of food to people through commercial fishing. Nevertheless, most peoples around the globe consume domestic plants and animals that are grown or raised locally or are produced commercially.

Climate and World Biomes

Climate (general, longer-term) and weather (specific, short-term) tend to structure ecosystems around the world by regulating rates of plant photosynthesis and production and contributing to patterns of vegetation and animal life. The principal factors are temperature, which is largely a function of global latitude and elevation; precipitation, drainage, and stored fresh water resources; windflow, which can dry or chill; solar radiation; and seasonal patterns in all of these, particularly temperature and rainfall. Polar and subpolar ecosystems, which are unsuitable for agriculture, are characterized by cold winters, cool summers, and limited precipitation. Some livestock are kept in polar and mountain ecosystems: llama and alpaca in the Andes, yak in the Himalayas, reindeer in the Arctic. Temperate and subtropical zone ecosystems may have relatively high precipitation, marked seasonality in temperature, and agricultural growing seasons up to six months. Drier temperate continental ecosystems (prairies, steppes) are also highly seasonal in rainfall with cold winters. Relatively dry, temperate zones can be highly productive with the practice of irrigation. Mediterranean ecosystems (including California, Chile, and parts of the Near East) have cool, wet winters and hot, dry summers. Many of the major cereal crops of the world were domesticated in these seasonally dry, temperate, or Mediterranean ecosystems: maize or corn in Middle America, wheat and barley in the Near East, rice in Asia, and sorghum in Africa. Quinoa, a member of the goosefoot family, was domesticated in the cool, seasonally dry reaches of the Andes. Tropical ecosystems have warm temperatures throughout the year but often with seasonality of rainfall. Those ecosystems with limited and seasonal rainfall grade into tropical grazing lands or savanna, while increased rainfall yields forests from sparse woodlands up to densely wooded rainforests. Widespread rainforest agriculture today includes a form of shifting, swidden, or slash-and-burn cultivation. Within each of these broadly-defined ecosystems or biomes, there is considerable variation: variation by season and by year, with inherent risks to livestock and agricultural production. For example, dramatic heat waves or cold periods, droughts, floods, hailstorms, and hurricanes can destroy crops and domestic livestock, producing a loss in food security and even famine. These extreme events have a major impact when they occur in heavily populated areas.

World Biomes and Food Production

Plants and animals were first domesticated in the seasonally dry Mediterranean climate of the Fertile Crescent in the Near East. These farming and livestock practices then spread along the Eurasian east-west axis zone of similar latitude and climate. Most domestic seed plants (e.g., cereals, goosefoots) and pulses (e.g., beans, lentils, grams, peas) were temperate-zone domesticates, whereas some tubers and root crops were domesticated in the tropics (e.g., manioc, yams, taro). With the discovery of the New World by Europeans, many native American foods spread to parts of the Old World: the potato became a staple in temperate zones of Europe and the Himalayas; maize became a staple in the drier African tropics; manioc became a staple in the wetter African tropics. Other New World temperate-zone domesticates, such as chocolate, peanuts, and tomatoes, became favored foods around the globe.

Today, temperate and subtropical agroclimatic zones of the United States, Argentina, Europe, and eastern Asia (China and Japan) still have the highest productivity of domestic grains and livestock that feed a substantial portion of the world. This results from a favorable combination of sophisticated agrotechnology and climate. Figure 1 illustrates how climatic inputs interact with the flows of information and resources in a Western industrialized system of agriculture.

Temperate and subarctic marine biomes are highly productive sources of fish and shellfish, although these food resources are in decline because of effective commercial exploitation by Western nations.

Food Intake and Climate

Some patterns of food intake are indirectly or directly linked to climate. For example, tropical populations are often limited in protein intake. Solomon Katz (1987) noted that this occurs in traditional agricultural populations dependent on grains (maize, rice, sorghum, millet) or tubers (potato, manioc) that are high in calories, but relatively lower in protein. Among tropical forest dwellers, as in the Amazon and the Congo basins, protein must come from fish, insects, some game animals, and plant foods. A direct effect of climate is the high metabolic need for calories in arctic or subarctic zones and temperate zone winters because of increased energy needs for temperature regulation in the cold. Derek Roberts (1978) documented that arctic dwellers have an elevated basal metabolic rate (BMR), which may be adaptive in the cold. Infants who are kept under cool conditions have higher food calorie requirements for normal weight gain than infants kept under warmer conditions. In Western industrialized nations, reduced activity levels during the winter season lead to unhealthy increases in the accumulation of human body fat (and weight) or energy storage. On the other hand, the accumulation of body fat in Ama women who dive for edible seaweed throughout the year allows them to withstand the cold water off the shores of Korea and Japan.

Climate Change and Food Production

An alarming trend that is certain to influence human patterns of food intake is recent climate change. Some variation in weather and climate is normal. Yet within the past 250 years, however, increased atmospheric carbon dioxide (CO₂), resulting from fossil fuel combustion, deforestation, and agricultural activities, has led to a "green-house" effect and global warming. A major compilation of research by Houghton and other scientists from the Intergovernmental Panel on Climate Change (IPCC) in 2001 has demonstrated beyond any reasonable doubt that human activities have produced a 1.1°F (0.6°C) rise in average global temperature over the past 150 years (see Figure 2). And by the year 2100, this global temperature is expected to rise another 1.8 to 6.3°F (1.0 to 3.5°C), a change that is greater than any experienced on the globe within the past ten thousand years.

Global warming will have variable effects on local weather and climate that are dependent on latitude, elevation, and geographic location. For example, McCarthy and others (2001) have shown that sea level rise from melting glaciers during the twentieth century has been about 6 inches (15 cm), and a projected rise during the twenty-first century is an additional 18.9 inches (48 cm). This will contribute to a loss of coastal agricultural lands and an increased salinization of water and coastal lands. Influences on agricultural food production are likely to be pronounced. Higher temperatures will cause rises in rainfall and the likelihood of floods in some areas and declines in rainfall and consequent drought in other areas: extremes in weather events (floods, hurricanes, heat waves, droughts) will be more common. Both conditions will lead to crop losses and decreased plant productivity. There will be increased heat stress in livestock leading to lower milk and meat production. At the same time that coastal agricultural and grazing land will be lost to sea level rise and salinization, the human population will continue to increase, putting greater pressure on food resources.

It is estimated that the impacts of global warming will be greatest in those regions of the world such as Asia, Africa, Latin America, and the Pacific Islands, where the adaptive capacity is low and vulnerability is high because of the lack of economic resources. Africa is likely to be especially hard hit because such a large part of its land resources is arid or semi-arid savanna lands. Of the total desertification and degradation around the globe, nearly 30 percent is in Africa. Although the debate continues on whether overgrazing, overpopulation, or warming trends are the cause of desertification, nevertheless, global warming will certainly increase the expanse of dry lands on this continent and elsewhere.

Humans have a remarkable capacity to adapt to change, including climate change, through culture and technology. Global warming and its consequent negative effects on our capacity to produce food will be an unprecedented challenge to this adaptability.

See also Agriculture, Origins of; Biodiversity; Food, Future of; Hunting and Gathering; Maize; Potato; Prehistoric Societies; Swidden.

Michael A. Little