Rising global temperatures, rapidly melting arctic ice and other effects of climate change are posing immediate risks to US national security and military and humanitarian operations, the Pentagon warned Monday.

In a comprehensive report billed as a roadmap for adapting to climate change, the Defense Department said it has begun to boost its "resilience" and ensure mission readiness is not compromised in the face of rising sea levels, increasing regularity of natural disasters, and food and water shortages in the developing world.

"Climate change will affect the Department of Defense's ability to defend the nation and poses immediate risks to US national security," according to the report.

"A changing climate will have real impacts on our military and the way it executes its missions."

The roadmap aims to adapt to climate change in part by integrating the risks into war games, strategic defense planning and how the military stores and transports supplies.

Defense Secretary Chuck Hagel, speaking at a conference in Peru on Monday, painted a bleak picture of how glacier loss, increasingly violent storms and drought-driven crop failures are already affecting millions of people, and may "trigger waves of mass migration."

"We have already seen these events unfold in other regions of the world, and there are worrying signs that climate change will create serious risks to stability in our own hemisphere," told a conference of defense ministers of the Americas.

"Our militaries' readiness could be tested, and our capabilities could be stressed," Hagel said, adding that the trends "will clearly have implications for our militaries."

"A higher tempo and intensity of natural disasters could demand more support for our civil authorities, and more humanitarian assistance and relief."

The challenges could undermine already-fragile governments and "create an avenue for extremist ideologies and conditions that foster terrorism."

The report said the Pentagon's "unique capability to provide logistical, material, and security assistance on a massive scale or in rapid fashion may be called upon with increasing frequency" as climate change intensifies challenges brought about by global instability.

The department said part of its mitigation efforts will focus on ways to reduce greenhouse gas emissions.

Hagel pointed to December's United Nations climate change convention to be held in Lima, and stressed that "defense leaders must be part of this global discussion."