There are many more climate impacts that could be very important but are not as well understood as those described above. Some illustrative examples are briefly provided here.

National Security

Many processes could plausibly connect climate change to national security concerns. For instance, military experts have pointed to the potential for climate-induced food and water shortages to contribute to political instability, which can then be exploited by extremists (CNA Corporation, 2007). The potential for mass migrations associated with resource shortages or flooding are also potential “threat multipliers.” Climate changes will also likely affect military operations, such as via inundation of low-lying military bases, and introduce new geopolitical dilemnas, such as the opening of sea routes in the Arctic.

Yet perhaps because of the complex nature of national security threats and the paucity of relevant data, there are relatively few quantitative examples that document the climate sensitivity of phenomena related to national security. Some empirical evidence suggests an important role for climate in domestic and international conflict. Long-term fluctuations of global wars and death rates since 1400 are correlated with shifts in temperature (Zhang et al., 2007a). In Africa, civil wars since 1980 have been roughly 50% more likely in years 1ºC warmer than average (Burke et al., 2009). Precipitation decreases are also associated with conflict in Africa, although projected rainfall changes are not large relative to historical variability (Miguel et al., 2004; Hendrix and Glaser, 2007).

Obviously more work is needed to advance understanding of national security threats from climate change. Specifically, although the implications of climate change for resource scarcity are uncertain, the complex relationship between resource scarcity and conflict is even more tenuously understood (Barnett, 2003; Nordås and Gleditsch, 2007). At the same time, military experts routinely caution that waiting for quantitative precision can be very risky, and intuition alone is often used to make major strategic decisions for national security (CNA Corporation, 2007).

Dynamic Vegetation

Changes in climate and CO2 beyond 2100 will likely be sufficient to cause large-scale shifts in natural ecosystems. Although relatively few

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