"...Climate change could have significant geopolitical impacts around the world, contributing to poverty, environmental degradation, and the further weakening of fragile governments. Climate change will contribute to food and water scarcity, will increase the spread of disease, and may spur or exacerbate mass migration."
Source: Quadrennial Defense Review Report (USA) Feb 2010
Bite notes Many sceptics think that climate change is the province of those with left-wing political views. So it might surpise them to discover then that the Western military have great concerns about the security impacts of climate change. The featured quote can be found at the top of page 85 of the report.
With lives at stake, military planners must be pragmatistic. Peering into the future, they have to anticipate threats, weigh risks and costs, and make decisions despite certainty. While generally conservative-leaning, they know that they face grave risks if they allow ideology or preconceptions to cloud their vision. So it's worth hearing what they have to say.
Also see Tools/Narratives/Security Climate Change as a National Security Threat and
The UK has identical defence concerns. A quote from The National Security Strategy of the United Kingdom.
Globally, climate change will increasingly be a wide-ranging driver of insecurity because it acts as a ‘threat multiplier’, exacerbating existing weakness and tensions around the world. It presents a challenge that goes far beyond direct physical disruption to the environment.
[Note: Defense is spelled with an "s" in the U.S., but with a "c" in England, Australia and Canada. Since the author is from the U.K., we defer to the British spelling, except for the Pentagon article cited above!]