7.6: Food and Water

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Perhaps the most consequential change will be in the spacetime distribution of rainfall. Elementary physics dictates that as the climate warms, rainfall must become increasingly concentrated; that is, when it rains it will rain substantially harder, but the frequency of rainstorms should decline. Also, areas that presently enjoy a wet climate will generally become even wetter, whereas arid regions will become more so, with only a small increase in globally averaged annual mean precipitation. Flash flooding will become more frequent, as will the incidence of drought. Climate model projections are consistent with these inferences from basic theory.

These changes in the hydrologic cycle, which are already underway, are especially worrying because of their effects on the supply of food and water. These will become apparent first and be most severe in regions, such as the Middle East, that today have only marginal food and/or water supplies

Figure \(\PageIndex{1}\): Number of extreme U.S. agricultural loss events per 20 years relative to the current 1-in-20 event, for three emissions scenarios. From Economic Risks of Climate Change: An American Prospectus.

Figure \(\PageIndex{1}\) shows a projection of the effect of climate change on U.S. agricultural losses, relative to today’s 1-in-20 event. By the end of this century, today’s 1-in-20 loss could occur every other year.

Historically, the disappearance of certain civilizations, such as that of the Anasazi in what is today the southwestern U.S., has been attributed to food and water shortages brought on by prolonged drought. Such shortages are also thought to cause or exacerbate mass migrations and armed conflict. The link between climate change and human conflict is well recognized in the defense community. For example, in its 2010 Quadrennial Defense Review, the U.S. Department of Defense states that:

climate change could have significant geopolitical impacts around the world, contributing to poverty, environmental degradation, and the further weakening of fragile governments. Climate change will contribute to food and water scarcity, will increase the spread of disease, and may spur or exacerbate mass migration.

Political and social destabilization of a crowded, nuclear armed world finely adapted to the highly stable climate of the last 7,000 years is perhaps the greatest and least predictable risk incurred by rapid climate change. Such existential risks are difficult to attach numbers to and represent extreme outcomes whose probability is not small under high-emissions scenarios.