A review of relevant data would lead one to be optimistic about the world's future capacity to feed itself under projected scenarios of climate change. On the whole, food production has kept up with population growth, the prices of cereals have been gradually declining, and trade models suggest that markets can move food effectively between countries and continents to compensate for deficits (Food and Agriculture Organization [FAO], 2003). Assuming that farmers can and will make adjustments in crop varieties, planting dates, irrigation applications, and the area they plant, research has shown that anticipated negative impacts of climate change on yields can be partially or perhaps even largely mitigated at the global scale (Helms et al., 1996; Rosenzweig and Parry, 1993).
However, when analyses are disaggregated at a regional level, these conclusions are not so optimistic. For example, maize is a crop that is central to the food security of much of Africa and Latin America. Changes in its yields are likely to be negative, particularly in lower latitude regions where it is more important to food security than in higher latitude regions (Rosenzweig and Parry, 1993). The latest Intergovernmental Panel on Climate Change (IPCC) report gives similar findings from modeling research of rice, millet, and wheat production under climate change scenarios, although the uncertainty in the models' outputs may prohibit any conclusive statements (IPCC, 2001).
Although the IPCC is also cautious about studies of future agricultural price changes (IPCC, 2001), several studies have also suggested that future cereal prices may rise anywhere between 10% and 200% with global warming greater than 2.5°C (Reilly, 1995). The precise numbers related to yield and price changes are uncertain; yet there is some concern that the stronger adaptive capacities of countries at higher latitudes will facilitate continued market dominance in cereal production, thus fostering increased dependence on food imports in many developing countries (Reilly and Schilm-melpfenning, 1999).
Such dependence is not necessarily a concern if prices continue on their negative trend. However, if cereal prices were to increase or become more volatile under progressive global warming, import-dependent countries would be negatively affected (IPCC, 2001). Countries already largely dependent on food imports would feel such impacts first (Parry, 1990; Reilly and Schilmmelpfenning, 1999). With rising food prices, the number of people at risk from hunger in developing nations would also rise by tens to perhaps hundreds of millions (Chen and Katz, 1994; Downing, 1996; Parry et al., 2001; Rosenzweig and Parry, 1993). Thus, while aggregate world food production may be able to keep up with population growth, the social consequences of climate change impacts in areas already struggling with high rates of poverty and malnutrition are cause for considerable concern.
The following section reviews the biophysical and social features that make tropical agricultural systems particularly vulnerable to climatic change, recognizing that it is not the physical region of the tropics that defines its vulnerability, but rather a complex combination of environmental, economic, and social characteristics at different scales that may have relatively little to do with latitude. This is particularly true when one focuses on the implications of climate change for regional food security, given that food security is essentially a social problem that typically involves historical inequities in resource distribution, the politics of resource access, and the differential capacities of population groups to exert an effective command over their basic necessities (Sen, 1981).
The analysis of maize and climate change in Mexico shows that while climatic impacts are not a determinant of food insecurity in the country, overall vulnerability is exacerbated when such impacts coincide with adverse trends in agriculture policy and rural welfare. Farmers, the government, and civic associations in Mexico have recently mobilized around the issue of food sovereignty or the power of the country's population to determine the content and quality of their diet according to their preferences whether through food imports or domestic production. There is some concern that climate change may not only contribute to a loss in productive capacity in agriculture, but also to a more intangible but troubling loss of control and command over the country's preferred food staple, maize.
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