The Complete Guide to Climate Change: Agriculture and Food Supply Impacts

The Complete Guide to Climate Change
by Brian Dawson

Sample Pages

AGRICULTURE AND FOOD SUPPLY IMPACTS

The impacts of climate change on agriculture must be viewed in the context of everincreasing demand for food and agricultural products. Agriculture currently accounts for nearly a quarter of world economic output and employment.1 The world’s population is growing rapidly, rising from 2.5 billion in 1950 to 6.5 billion in 2005 and to an expected 9 billion by 2050.2 As per capita incomes rise in industrializing countries such as China and India, so too will the demand for food and, in particular, meat – which will in turn necessitate increases in fodder crop supplies. If biofuels production also expands, so too will the area devoted to source crops.

Global crop production will have to increase significantly over the coming decades to meet these demands.3 Under normal circumstances, ongoing improvements in crop yields (due to technical advances and irrigation) and expansion of the amount of land under crop might be sufficient to meet the growing demand. However, “normal circumstances” are unlikely to prevail over the coming decades since climate change is expected to affect the environmental factors that determine global crop production.

Crop yields and agricultural production are primarily determined by soil moisture, temperature, sunlight, and soil fertility. Over the course of this century, climate change is expected to lead to higher average global temperatures, changes in annual and seasonal precipitation patterns (see water impacts), and increases in the frequency and intensity of extreme weather events. Elevated concentrations of atmospheric carbon dioxide (CO2) could also influence crop yields through the CO2 fertilization effect. These factors will fundamentally alter crop yields and the distribution of agricultural production. In some regions, changes in climatic conditions might improve crop yields, as is expected in the higher latitudes of Europe and North America. However, in most other regions, changes in temperature and water availability are expected to result in reduced yields, particularly in tropical regions, where temperatures are already at, or exceeding, optimal conditions for plant growth. Climate-induced changes in biodiversity and ecosystems – such as reductions in the abundance of essential crop pollinators (such as bees) or natural insect control species (such as insect-eating birds) could also affect yields, as could expansions in the geographical ranges of pests and diseases.

Temperature and rainfall impacts

Different crops require different temperature and soil moisture regimes for optimum yields. Water is generally the major limiting factor with regard to crop production. If there is insufficient soil moisture, as occurs during droughts, or there is too much, as occurs during floods or periods of excessive precipitation, yields decline and can even result in total crop loss. Most crops are very sensitive to temperatures above 35-40ºC as photosynthetic functioning can be impaired. Elevated temperatures tend also to reduce the growing period between sowing and harvest, thereby reducing the amount of light captured and the resulting biomass production.

The prevailing rainfall and temperature regime is a key determinant of the types of crops farmers choose to grow. The world’s principal wheat, oat, and barley production regions, for example, are located in mid-latitude regions such as Australia and central USA, where winter and spring rains are reliable and where summers are warm and dry. Wheat is not suited to warm, wet conditions, such as those found in the humid tropics and subtropics, or to the cold, high-latitude regions where the growing season is too short. Rice, on the other hand, generally requires warm and wet conditions during the growing cycle to obtain optimum yields and is well suited to tropical regions and areas that have warm monsoonal regimes. As climate regimes evolve and migrate, so too will the crops that can be grown.

Note: The rest of the chapter is omitted.