Projected Trends in Extreme Weather Events
| Phenomenon | Likelihood of Changes in 2016-2035 | Likelihood of Changes by 2080-2100 |
|---|---|---|
| Warmer days and nights | Likely | Virtually certain (99-100%) |
| More hot days and nights | Likely | Virtually certain |
| More warm spells and heatwaves | Likely | Very likely (90-100%) |
| More heavy precipitation events | Likely | Very likely |
| More droughts | More likely than not | Likely (66-100%) |
| More intense tropical cyclones | More likely than not | More likely than not (33-66%) |
| More extreme sea levels | Likely | Very likely |
Source: Intergovernmental Panel on Climate Change, Fifth Assessment Report, September 2013
Effects of Climate Change on National Security: Possible Pathways
Climate and weather have long affected the national security of countries worldwide, although most often as a contributing factor that might be recognized only in retrospect. Sometimes the effects are dramatic—such as the brutal Russian winter that contributed to Hitler’s failed invasion in World War II— but more often weather and climate exert indirect effects that shape underlying social, political, and economic conditions. Academic research on the impacts of climate on political and security outcomes is still sparse, but we judge that climate will affect US national security interests over the next 20 years through the following pathways.
Threats to the Stability of Countries
Many countries will encounter climate-induced disruptions—such as weather-related disasters, drought, famine, or damage to infrastructure—that stress their capacity to respond, cope with, or adapt. Climate-related impacts will also contribute to increased migration, which can be particularly disruptive if, for example, demand for food and shelter outstrips the resources available to assist those in need.
When climate-related effects overwhelm a state’s capacity to respond or recover, its authority can be so undermined as to lead to large-scale political instability. Countries with weak political institutions, poor economic conditions, or where other risk factors for political strife are already present will be the most vulnerable to climate-linked instability. In the most dramatic cases, state authority may collapse partially or entirely. Climate-related instability is likely to create strong pressure for foreign aid, disaster assistance, or military responses. Even if climate-related disruptions do not undermine stability, however, some
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