Here are key moments from President Obama's commencement address to the Coast Guard Academy class of 2015, in which he told the graduates climate change would affect "everything that you do in your careers." (WhiteHouse.gov)

"We have a little bit of money devoted to a comprehensive, worldwide effort to deal with the threat of global warming," the president said. "It is simply a matter of science and evidence. It is … necessary to reverse it to stand up for America's values and America's interests."

Given that we've employed the standard trick of not naming the president, you may have guessed that the quote above doesn't come from President Obama's remarks at Wednesday's Coast Guard Academy commencement. In that speech, Obama linked the security of the country with the threat of climate change in the same way. But the comments above instead come from a speech about two decades ago -- by President Bill Clinton.

The most remarkable thing about Obama's Coast Guard comments, in which he argued that we must address the threat of climate change if only to decrease global instability and risks to U.S. facilities, is that it's the refrain to a long-running tune. The link between our security and our carbon emissions has been drawn time and again.

Within Obama's two terms, the drumbeat has been consistent. In 2009, the Navy looked at maritime security risks posed by climate change. In 2011, Rear Adn. David Titley gave a talk at TedxPentagon (!) that considered the issue. (That speech is below.) In 2012, a major general from the U.S. Northern Command warned that melting Arctic ice would create a new, northern coast that would enter into geopolitical considerations. And last year, the Pentagon released a report stating that "[o]ur armed forces must prepare for a future with a wide spectrum of possible threats, weighing risks and probabilities to ensure that we will continue to keep our country secure."

In 2003, the Pentagon drafted a speculative plan that addressed the national security threat from an abrupt change to the world's climate -- a shift of several degrees of temperature in a matter of a decade or so. It garnered a substantial amount of attention at the time, but was mostly regarded as a thought experiment. Consensus remains that such a temperature change will happen much more slowly.

But military experts under President George W. Bush were addressing the more realistic, slower effects of climate change, too. We reported in 2007 that the U.S. Army War College funded a conference to address the security implications of climate change. That was soon followed by a report from a panel of retired military leaders that was blunt: "Global climate change presents a serious national security threat which could impact Americans at home, impact United States military operations and heighten global tensions." DARPA started looking into military use of biofuels before Bush left office.

Under Clinton, the administration was open in its advocacy on the issue, even if the military was more reserved. Vice President Al Gore had already called climate change "the most serious threat we have ever faced" in his book "Earth in the Balance" by the time Clinton was moving into 1600 Pennsylvania Avenue. After Clinton signed the Kyoto Protocol aimed at reducing carbon dioxide emissions, House Republicans and retired military officials at that point worried that the protocol itself posed a national security risk, given that it required the reduction of energy use -- and the military used more energy than any other part of the government. In response, Clinton exempted the military from being affected.

A link between national security and the climate even predates Clinton. In June 1988, a Senate committee addressed the problem of climate change for the first time, hearing testimony from several scientists, including James Hansen, then of NASA Goddard Space Flight Center and who since has been an outspoken activist on the subject. After that hearing, Michael Oppenheimer of the Environmental Defense Fund was asked to clarify some of his comments. In a responding letter, he wrote, "For the U.S., continuous emissions at current levels or higher means continuous change, loss of ecosystems, and probably loss of farm productivity, wetlands, beaches and coastal infrastructure. The security of the nation depends on stabilization of the atmosphere."

At the Coast Guard Academy on Wednesday, President Obama played the same tune.