Fundamental characteristics of the global climate are moving outside the bounds experienced in human history and there is uncertainty on how some aspects of the climate will evolve. Given the social and political contexts in which a multitude of changes are occurring, however, we can expect new and compounded stresses on people and societies around the world, many with outcomes important for national security.

Climate change will have wide-ranging implications for U.S. national security over the next 20 years through global perturbations, increased risk of political instability, heightened tensions between countries for resources, a growing number of climate-linked humanitarian crises, emergent geostrategic competitive domains and adverse effects on militaries, increasingly probable amalgamations of these security concerns are especially worrisome. Climate change alone is unlikely to trigger state failure in the next few decades but it will affect factors that that contribute to conflict, such as access to natural resources. People will increasingly decide to move because of deteriorating conditions, both within nations and into countries that are more prosperous. Perhaps most importantly, the rapidity of concurrent and compounded changes to Earth’s systems, from human and natural causes, heightens the risk for unwelcome and possibly severe climate-linked surprises.