Of all the potential impacts of climate change, it is the threat to the food supply that is perhaps the most frightening. With more than six billion mouths to feed and only so much arable land on which food can be grown, the margin for crop failure is shrinking. Food abundance, the norm for the past several decades, is beginning to give way to scarcity. For example, global droughts during the 2007 growing season led to shortfalls of millions of metric tons of grains, forcing exporting powers like Australia to have to consider importing to meet internal demands. Protests have been launched against the increased price of tortillas in Mexico and pasta in Italy. The United Nation's World Food Programme (WFP) has seen operating costs jump 50 percent since 2002, and expects another 35 percent rise by 2010.
One benefit of climate change is the expansion of vineyards in the United Kingdom: the last time wine was produced on a such a wide scale in England was during the Medieval Climate Optimum of 800-1300 c.E., before the Little Ice Age of the 16th to the mid-19th centuries. Warmer temperatures are expected to expand growing seasons in regions close to the poles, opening up new land to agricultural development, particularly in the northern latitudes. Climate zones may move north by anywhere between 100350 mi. (161-563 km.), and up 500-1,800 ft. (152585 m.) in elevation. Some current climate zones will disappear completely, while new microclimates will be created.
Another potential benefit of global warming will be the fertilization effect of carbon dioxide (CO2). Carbon dioxide is a plant nutrient that, under optimal conditions, can stimulate and enhance photosynthesis. It can also improve a plant's ability to use water by inhibiting transpiration, the evaporation of water out of organic material. Higher CO2 concentrations could also mitigate the damaging effects of other environmental pollutants, such as SO2, the main pollutant in acid rain. Over 90 percent of the world's crops could theoretically benefit from CO2 fertilization, although some staple crops like maize, sorghum, millet, and sugar cane would not. A 1990 study estimated that it could increase crop productivity 10 to 20 percent over the next century.
Crop growth is implicitly tied to air temperature. Higher temperatures speed a plant's development, which for farmers means a shorter period between the planting and harvesting of crops. In some areas, planting will be able to begin earlier in the calendar year, and temperatures may allow multiple planting cycles in a season. But outside the northern latitudes, the impact of higher temperatures becomes a negative. Prolonged periods of 90 to 100 degree F weather causes severe damage to most crops. Heat-stressed livestock do not thrive, with high temperatures reducing, for example, milk production.
The same fertilizing effects of CO2 seen in plants also work on weeds, which may become more invasive in a warming world. This will require heavier application of weed-controlling agents, most of which emit greenhouse gases as they break down, to protect threatened crops. Insects and pests are likely to take advantage of warmer winters and move into new regions; a longer period of summertime warmth will also allow some destructive insects, like grasshoppers, to go through several reproductive cycles in a single year, maximizing the potential damage. Bacteria and fungi will take advantage of new wind patterns and warmer, wetter conditions to bloom.
Higher temperatures also have an effect on soil quality. Warmer soil breaks down organic matter more quickly, stripping it of nutrients and requiring the use of more fertilizers to enhance soil fertility. These, like pesticides and herbicides, emit pollutants. Dried-out soil is also more prone to erosion. Precipitation patterns are expected to change dramatically over the next century. Climate scientists expect that there will be more prolonged dry spells, punctuated by brief, heavy downpours. This will have a negative impact on crop yield, because most staple crops are sensitive to drought stress. Heavy rain falling on very dry soil exacerbates soil erosion. Increased risk of flooding raises the likelihood of crop damage or outright destruction. Aside from the increased risk of drought, farmers will also have to face an overall reduction in available water for irrigation, stemming both from changes in the global hydrologic cycle and an increasing urban population.
There are a number of ways farmers could adapt to climate change, ranging from very simple techniques such as changing their sowing dates to take advantage of an earlier spring, to the more complex options including developing methane-recovery systems that sequester livestock manure into digesters and turn them into biogas. While the use of genetically modified (GM) crops remains controversial in many parts of the world, gene manipulation could create crops that are more resistant to many of the situations that might present themselves in a warming world.
SEE ALSo: Agriculture; Food Miles; Impacts of Global Warming; Plants.
BIBLIoGRAPHY. Food and Agriculture Organization, www. fao.org (cited November 2007); Livestock, Environment, and Development LEAD Initiative, www.virtualcentre.org (cited November 2007); Overseas Development Institute, www.odi.org.uk (cited November 2007).
Heather K. Michon Independent Scholar
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