There may not have been a single question about climate change in the 2016 presidential debates, but it remains a hotly contested, partisan issue for many in the United States. That climate change is happening and requires a response is not up for debate within the upper echelons of the U.S. military, however.

Many hearings, reports, and candid observations have given testimony to this. But for those still wondering if political pressure is behind it all, a new issue of the U.S. Marine Corps Press Journal outlines some of the recent history of climate change policy in the U.S. military, from Nixon to Obama.

The special issue of the peer-reviewed journal is its first foray into climate change and the editors acknowledge it is a new direction. “Readers might wonder how this global topic impacts the U.S. Marine Corps; however, the two are not such disparate concepts, particularly when we consider the connection between climate change impacts and humanitarian aid and disaster relief operations the Corps has supported as early as 1895,” write the editors. “While it is not our intent to take a political or philosophical stance on the issue, we do intend to use this medium to inspire discussion on how U.S. agencies and Service branches address the subject based on operational demands, political pressure, and public opinion.”

The five articles, four book reviews, plus an introduction run the gamut from an examination of how climate change is impacting operations in the Pacific and a breakdown of two centuries of public dialogue on climate change to how the Office of Operational Energy is different than past efforts to “green” the military.

The introduction by Edward J. Erickson, a professor at the Marine Corps University and retired U.S. Army officer, is a concise summary of how climate change has been incorporated into the Pentagon’s operations and policy over the last decade. He traces the transition “from passive neglect in 2006 to active concern in 2015,” instigated through a mix of presidential direction and an evolution of priorities within the department itself.

The 2010 National Security Strategy, President Obama’s first, was also the first to introduce U.S. government climate policy (though Nixon received and seemed to seriously consider a memo on climate change from White House Counsel Daniel Patrick Moynihan). The National Security Strategy, which is prepared by the White House, gives direction to the military but also other branches of government, and in 2010 it noted “the danger from climate change is real, urgent, and severe.”

Afterwards, the Pentagon produced a Quadrennial Defense Review in 2010, an every-four years report to Congress on priorities, threats, and doctrine, and a National Military Strategy in 2011, which describes expected activities and resource allocations. Both of these documents take direction from the National Security Strategy, but otherwise were produced by the military itself and reflect how conceptions of climate change were evolving.

The Quadrennial Defense Review “presented climate change as a problem to be dealt with rather than a problem to be solved,” writes Erickson, noting a focus on the operating environment and how climate change will affect various missions and roles. The 2011 strategy, headed by the Chairman of the Joint Chiefs of Staff Admiral Mike Mullen, introduced the idea that demographics will affect strategic risk. Increasing population density in “underdeveloped littoral areas” may make some countries more vulnerable to natural disasters.

In 2014, the next Quadrennial Defense Review reiterated that the U.S. military considers climate change a serious risk, and the Department of Defense released a climate adaptation roadmap in response to executive orders from the White House (the 2014 roadmap is actually the second iteration for the department, but the 2012 version has apparently been taken offline).

“While some might assume that DOD officials are just going through the motions in terms of implementing climate change policies,” writes Erickson, “the stipulations for adaptation, and even mitigation, are leading to extensive changes in the department that trickle down into the activities of various U.S. military branches worldwide.”

Indeed, in response to a congressional inquiry in 2015 asking for specific examples of how climate change was affecting each of the Geographic Combatant Commands (e.g., U.S. Central Command, which coordinates activities in the Middle East and Central Asia), the Pentagon quickly released a detailed response. “The Department of Defense sees climate change as a present security threat, not strictly a long-term risk,” the report reads. Each of the Geographic Combatant Commands “share a common assessment of its significance” and “incorporate the risks posed by current and projected climate variations into their planning, resource requirements, and operational considerations.”

Over the last 10 years, Erickson notes a trend from “from generalizations to explicit understandings about risk, adaptation, and mitigation.” The 2015 National Security Strategy listed eight major risks in order of priority, with climate change coming in at number six – more important than a disruption to the energy market or failed states, but behind an attack on the homeland or allies, a global economic crisis, weapons of mass destruction, and a severe global disease outbreak. The incorporation of climate change into strategy, planning, and doctrine is notable – and the political dialogue has clearly not caught up.

“The DOD has positions and policies about climate changes that are unrelated to causal agencies,” Erickson writes, alluding to debate about whether climate change is man-made. “As a matter of policy, the DOD accepts climate change as a reality affecting the present and future operating environment and accepts that American military forces must deal with its operational consequences.”

“Regardless of whether the high-level policy decisions resolve themselves, there is absolutely no question that the DOD will have to deal with the real-world consequences of climate change, man-made or otherwise, that have been seen in recent years,” he concludes. “Instability driven by natural disasters, migration, and water and food scarcity will surely continue into the future, and American service members will find themselves at the intersection of politics and actual events.”