not occurred. But while direct vulnerability to events that limit local food production has decreased, vulnerability, especially of the lowest-income groups, remains and may be increased with respect to events that limit distribution or that sharply increase prices in global markets for necessities that cannot be acquired locally. Economic globalization thus changes the nature of vulnerability to climate events as well as the degree of that vulnerability (Leichenko and O’Brien, 2008). With globalization, populations become increasingly interconnected via international trade so that it becomes possible, for example, for a climatic event that affects one of the world’s grain-producing regions to influence global commodities markets in ways that can seriously affect populations that do not directly experience the climate event. In this way the well-being of households in Lagos or Nairobi can be sharply affected by a drought in Ukraine or the United States. Security analyses should consider the possibility of this sort of phenomenon in commodity markets when assessing the climate vulnerabilities of large low-income populations in key countries.

Climate and Ecological Change

Societal activities are well known to alter ecosystems. Climate change also does this—sometimes slowly, and sometimes as the result of extreme events—with results that may not become evident until an extreme climate event occurs. For example, climate change can alter the ranges of certain species of pests or pathogens, increasing the exposure of human populations or economically important nonhuman species. The expansion of the pine bark beetle in North America is a familiar example. As average temperatures in the region increased, making additional areas suitable for beetle infestations, the beetle expanded its range northward and toward higher elevations (Carroll et al., 2003). The ecological change did not become seriously disruptive to human populations until the increased prevalence of dead trees combined with drought and hot weather to produce major wildfires that affected populated areas. The wildfires in Colorado in 2012, widely described as unprecedented in extent, may have been affected by this process.

Slow climate change could potentially have similar effects on the evolution or distribution of human pathogens (influenza, yellow fever, etc.) or of pests of major crop or livestock species. When one of these pests or pathogens makes contact with a vulnerable population, epidemics, epizootics, or crop failures can spread rapidly, leading to major losses of human life and well-being. Slow processes of ecological change or slow changes in the resistance of host populations to disease organisms could lead to the crossing of a tipping point in vulnerability, at which point the meeting of pest and host populations can set off a highly disruptive chain of events.

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