At present, the growing implications for humans of extreme weather events suggest that climate-change related disruptions are well underway (see following map for illustrative examples of recent extreme weather events). Individual weather occurrences remain difficult to attribute entirely to climate change, however.
Looking forward, we assess that during the next five years national security risks linked to climate change will arise mostly from distinct extreme weather events, especially in regions with weak governance, poor living conditions, or persistent conflict that limit the capacity of governments and societies to cope with additional stress. When extreme events occur where they have not before, that too will be disruptive, even for advanced industrial countries.
We assess that during the next 20 years—in addition to increasingly disruptive extreme weather events—climate change effects will play out in broader, systemic ways, such as more acidic oceans, degraded soil and air-quality, and rising sea levels, resulting in sustained direct and indirect effects on US national security. Weather events of modest severity will be disruptive when their impacts are compounded as part of a rapid sequence or in clusters.
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