The gist is that the Pentagon's futurists foresee a world where our changing climate has tremendous real-world effects, and they want to be ready. Lots of people know the climate is changing, but given the Pentagon's budget, it's nice to know they are preparing to protect us from things that might actually harm us (and not, for example, on potentially useless helicopter engines). In the 2014 CCAR, the Secretary of Defense, Chuck Hagel, writes that the Department of Defense will focus on just those sorts of threats:
The plan is laid out in some detail in a 20-page PDF that talks about how recurrent flooding is already affecting the Hampton Roads area of Virginia, "which houses the largest concentration of US military sites in the world" (page 2) and how "climate change will have serious implications for the Department's ability to maintain both its built and natural infrastructure, and to ensure military readiness in the future" (page 8). The Pentagon is also aware that it will likely need to conduct more humanitarian missions after natural disasters and it will need to have its weapons work no matter what the weather is like out there. We'll see if the message is heard this time.
A changing climate will have real impacts on our military and the way it executes its missions. The military could be called upon more often to support civil authorities, and provide humanitarian assistance and disaster relief in the face of more frequent and more intense natural disasters. Our coastal installations are vulnerable to rising sea levels and increased flooding, while droughts, wildfires, and more extreme temperatures could threaten many of our training activities. Our supply chains could be impacted, and we will need to ensure our critical equipment works under more extreme weather conditions. Weather has always affected military operations, and as the climate changes, the way we execute operations may be altered or constrained.
While scientists are converging toward consensus on future climate projections, uncertainty remains. But this cannot be an excuse for delaying action.