National Aeronautics and Space Administration


Date of this Version



Science (319): 580-581 (February 2008).


Some of the most profound and direct impacts of climate change over the next few decades will be on agricultural and food systems. On page 607 of this issue, Lobell et al. (1) show that increasing temperatures and declining precipitation over semiarid regions are likely to reduce yields for corn, wheat, rice, and other primary crops in the next two decades. These changes could have a substantial impact on global food security.

Since the 1990s, rising commodity prices and declining per capita cultivated area have led to decreases in food production, eroding food security in many communities (2). Many regions that lack food security rely on local agricultural production to meet their food needs. Primarily tropical and subtropical, these regions are substantially affected by both global climate variations and global commodity price fluctuations. Warming in the Indian Ocean (3) and an increasingly “El Nino–like” climate (4) could reduce main-season precipitation across parts of the Americas, Africa, and Asia (see the figure).

In food-insecure regions, many farmers both consume their product and sell it in local markets. This exposes farmers to climate variations, because when they produce less their income goes down while their costs go up to maintain basic consumption. Large-scale hunger can ensue, even when there is sufficient food in the market that has been imported from elsewhere.

National revenue can also be affected by large-scale droughts, which restrict the ability of countries with small budgets to purchase grain on the international market. Thus, recent large increases in grain prices reduce access to food for the poor, for example, in Tanzania, who compete for corn with ethanol producers and hog farmers in the United States. Finally, up to half of all malnutrition is driven by nonfood factors through diseases such as HIV/AIDS and malaria; the latter disease is likely to become more severe and widespread with warming temperatures.

Lobell et al. use crop models to calculate changes in agricultural production to 2030. The results show that climate change is likely to reduce agricultural production, thus reducing food availability. Identifying the impact of this reduced production will, however, be complicated by other changes. The latter include rising oil prices, the globalization of the grain market, and a structural change in demand for key food supplies due to increasing demand for biofuels and rising per-capita consumption in India and China. These changes have pushed up supply costs for staple foods by 40% or more in many food-insecure areas. Decoupling these effects to implement mitigation and adaptation programs will be difficult.

Climate change impacts on farmers will vary by region, depending on their use of technology. Technological sophistication determines a farm’s productivity far more than its climatic and agricultural endowments. Food insecurity, therefore, is not solely a product of “climatic determinism” and can be addressed by improvements in economic, political, and agricultural policies at local and global scales. In currently food-insecure regions, farming is typically conducted manually, using a hoe and planting stick with few inputs. The difference between the productivity of these farms and those using petroleum-based fertilizer and pesticides, biotechnology-enhanced plant varieties, and mechanization is extreme (5). Not only will climate change have a differential effect on ecosystems in the tropics due to their already warmer climates, but also poor farmers in the tropics will be less able to cope with changes in climate because they have far fewer options in their agricultural system to begin with. These handicaps can be exacerbated by macro-economic policies that create disincentives for agricultural development, such as agricultural subsidies in the United States and Europe and poorly implemented cash transfer programs (6).