Washington (CNN) President Barack Obama used his commencement speech to the U.S. Coast Guard Academy in New London, Connecticut on Wednesday, to focus on a topic he called an immediate national security threat: climate change.

"Climate change will impact every country on the planet. No nation is immune," the President told the 218 graduating cadets. "Climate change constitutes a serious threat to global security, an immediate risk to our national security, and, make no mistake, it will impact how our military defends our country. And so we need to act — and we need to act now."

President Obama stressed the effects of climate change and its role in natural disasters and humanitarian crises, citing potential increases in refugee flows, a lack of food and water and threatening the readiness of U.S. military forces.

"Many of our military installations are on the coast, including, of course, our Coast Guard stations. Around Norfolk, high tides and storms increasingly flood parts of our Navy base and an air base. In Alaska, thawing permafrost is damaging military facilities. Out West, deeper droughts and longer wildfires could threaten training areas our troops depend on."

Earlier this month, the Obama administration, citing "rigorous safety standards" and a long review process, granted conditional approval to energy giant Shell to begin oil drilling in the Arctic waters off the coast of Alaska.

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