Climate Change Information Sheet 10

Agriculture and food security

• Some agricultural regions will be threatened by climate change, while others may benefit. The impact on crop yields and productivity will vary considerably. Added heat stress, shifting monsoons, and drier soils may reduce yields in the tropics and subtropics, whereas longer growing seasons may boost yields in northern Canada and Europe. Projections of regional climate change and the resulting agricultural impacts, however, are still full of uncertainties (as illustrated by the table below).
• Climate and agricultural zones are likely to shift towards the poles. Because average temperatures are expected to rise more near the north and south poles than near the equator, the shift in climate zones will be more pronounced at higher latitudes. In the mid-latitude regions (45^o to 60^o), present temperature zones could shift by 150–550 km. Since each of today's latitudinal climate belts is optimal for particular crops, such shifts could strongly affect agricultural and livestock production. Efforts to shift crops poleward in response could be limited by the inability of soil types in the new climate zones to support intensive agriculture as practiced today in the main producer countries.
• Soil moisture will be affected by changing precipitation patterns. Based on a global warming of 1–3.5^oC over the next 100 years, climate models project that both evaporation and precipitation will increase, as will the frequency of intense rainfalls. While some regions may become wetter, in others the net effect of an intensified hydrological cycle will be a loss of soil moisture. Some regions that are already drought-prone may suffer longer and more severe dry spells. The models also project seasonal shifts in precipitation patterns: soil moisture will decline in some mid-latitude continental regions during the summer, while rain and snow will probably increase at high latitudes during the winter.
• Higher temperatures will influence production patterns. Plant growth and health may benefit from fewer freezes and chills, but some crops may be damaged by higher temperatures, particularly if combined with water shortages. Certain weeds may expand their range into higher-latitude habitats. There is also some evidence that the poleward expansion of insects and plant diseases will add to the risk of crop loss.
• More carbon dioxide in the atmosphere could boost productivity. In principle, higher levels of CO₂ should stimulate photosynthesis in certain plants. This is particularly true for so-called C3 plants because increased carbon dioxide tends to suppress their photo-respiration, making them more water efficient. C3 plants make up the majority of species globally, especially in cooler and wetter habitats, and include most crop species, such as wheat, rice, barley, cassava and potato. The response of C4 plants would not be as dramatic. C4 plants include such tropical crops as maize, sugar cane, sorghum and millet, which are important for the food security of many developing countries, as well as pasturage and forage grasses. Experiments based on a doubling of CO₂ concentrations have confirmed that "CO₂ fertilization" can increase mean yields of C3 crops by 30%. This effect could be enhanced or reduced, however, by accompanying changes in temperature, precipitation, pests, and the availability of nutrients.
• The productivity of rangelands and pastures would also be affected. For example, livestock would become costlier if agricultural disruption leads to higher grain prices. In general, it seems that intensively managed livestock systems will more easily adapt to climate change than will crop systems. This may not be the case for pastoral systems, however, where communities tend to adopt new methods and technologies more slowly.
• The global yield from marine fisheries should remain unchanged by global warming. The principal effects will be felt at the national and local levels as the mix of species changes and people respond by relocating fisheries. These possible local effects could threaten the food security of countries that are highly dependent on fish. In general, some of the positive effects of climate change could include longer growing seasons, lower natural winter mortality, and faster growth rates at higher latitudes. The negative ones could include upsets in established reproductive patterns, migration routes, and ecosystem relationships.
• Food security risks are primarily local and national. Studies suggest that global agricultural production could be maintained relative to the expected baseline levels over the next 100 years. However, regional effects would vary widely, and some countries may experience reduced output even if they take measures to adapt. This conclusion takes into account the beneficial effects of CO₂ fertilization but not other possible effects of climate change, including changes in agricultural pests and soils.
• The most vulnerable people are the landless, poor, and isolated. Poor terms of trade, weak infrastructure, lack of access to technology and information, and armed conflict will make it more difficult for these people to cope with the agricultural consequences of climate change. Many of the world's poorest areas, dependent on isolated agricultural systems in semi-arid and arid regions, face the greatest risk. Many of these at-risk populations live in sub-Saharan Africa; South, East and Southeast Asia; tropical areas of Latin America; and some Pacific island nations.
• Effective policies can help to improve food security. The negative effects of climate change can be limited by changes in crops and crop varieties, improved water-management and irrigation systems, adapted planting schedules and tillage practices, and better watershed management and land-use planning. In addition to addressing the physiological response of plants and animals, policies can seek to improve how production and distribution systems cope with fluctuations in yields.

Selected crop studies of future climate change

Region                                Impact on yields (%)                                  Maize                Wheat Latin America            -61 to an increase        –50 to –5
Former Soviet Union            -                   –19 to +41
Europe                   –30 to an increase      increase or decrease
North America            –55 to +62                 –100 to +234
Africa                   –65 to +6                     -
South Asia               –65 to –10                 –61 to +67 Other Asia and Pacific Rim     -                    –41 to +65

Source: Intergovernmental Panel on Climate Change, "Summary for Policymakers: Scientific-Technical Analysis of Impacts, Adaptations, and Mitigation of Climate Change", p. 10, in "Climate Change 1995", Vol. 2, Cambridge University Press.