Climate-driven crises could lead to internal instability or international conflict and might force the United States to provide humanitarian assistance or, in some cases, military force to protect vital energy, economic or other interests, the study said.

The Defense Department has already taken major steps to plan for and adapt to climate change and has spent billions of dollars to make ships, aircraft and vehicles more fuel-efficient. Nonetheless, the 206-page study warns in sometimes bureaucratic language, the United States is ill prepared to assess and prepare for the catastrophes that a heated planet will produce.

“It is prudent to expect that over the course of a decade some climate events — including single events, conjunctions of events occurring simultaneously or in sequence in particular locations, and events affecting globally integrated systems that provide for human well-being — will produce consequences that exceed the capacity of the affected societies or global system to manage and that have global security implications serious enough to compel international response,” the report states.