If we’re going to increase defense spending, we should consider targeting the enemy.

The budget President Trump released this month increases Defense Department spending by $54 billion, or 10 percent. It increases Homeland Security expenditures by almost 7 percent. At the same time, it decreases spending by the Environmental Protection Agency by an astounding 31 percent, and eliminates EPA spending on climate programs. “As to climate change…we’re not spending money on that anymore,” according to Mick Mulvaney, the Director of the Office of Management and Budget. It’s “a waste of your money.”

That’s a mistake. The failure to address climate change has profound security implications. Environmental advocates are not the only ones who hold this view; U.S. defense and intelligence agencies have long shared the concern.

A Pentagon analysis released in 2004 evinces a particularly dystopian view of the climate threat: “Disruption and conflict will be endemic features of life.” The report is especially noteworthy in that it was commissioned by well-respected Pentagon advisor Andrew Marshall. According to a February 21, 2004 report in The Guardian, Marshall “is a Pentagon legend …dubbed ‘Yoda’ by Pentagon insiders” in recognition of his vast experience.

In 2007, a report commissioned by the Center for Naval Analyses and including 11 retired generals — eight four-star and three three-star — released a study saying that global warming “presents significant national security challenges to the United States,” which the U.S. must address or face serious consequences. It refers to climate change as “a threat multiplier for instability in some of the most volatile regions of the world,” in part by causing water shortages and damaging food production. According to the report, 40 percent of the world’s population gets at least half its drinking water from mountain glaciers that are now disappearing.

In a study commissioned by the C.I.A., the National Research Council said in 2012 that the U.S. is unprepared to address the catastrophes that climate change will create. The study says that over the next decade there will be climate events with “consequences that exceed the capacity of the affected societies or global system to manage and that have global security implications serious enough to compel international response.”

I agree that the effects of a changing climate... impact our security situation. Secretary of Defense James Mattis

In 2014 the Pentagon released a report referencing the dangerous impacts of climate change on food and water supplies, damage to infrastructure, the spread of disease, and mass migration. The report said: “These developments could undermine already-fragile governments that are unable to respond effectively or challenge currently-stable governments…. These gaps in governance can create an avenue for extremist ideologies and conditions that foster terrorism.”

In that report the Pentagon highlighted the vulnerability of the military’s 7,000 bases and other installations. It warned that “in places like the Hampton Roads region in Virginia, which houses the largest concentration of US military sites in the world, we see recurrent flooding today, and we are beginning work to address a projected sea-level rise of 1.5 feet over the next 20 to 50 years.”

Even President Trump’s recently confirmed Secretary of Defense, James Mattis, provided written comments along these same lines to the Senate Armed Services Committee. In January, Secretary Mattis said: “I agree that the effects of a changing climate — such as increased maritime access to the Arctic, rising sea levels, desertification, among others — impact our security situation.”

This is not the first time Secretary Mattis has opined on climate change and its military implications. In 2010, the United States Joint Forces Command released a document entitled “The Joint Operating Environment.” The Foreword is signed “J.N. Mattis, General, U.S. Marines Commander, U.S. Joint Forces Command.” The report lists climate change “as one of the ten trends most likely to impact the Joint Force.” It references shrinking Arctic sea ice as opening new areas for natural resource exploitation that may raise tensions among Arctic nations. It cites a 2007 event in which “two Russian submersibles made an unprecedented dive 2.5 miles to the arctic sea floor, where one ship dropped a titanium capsule containing a Russian flag.”

Referencing sea level rise caused by climate change, the Joint Forces Command report notes that “one-fifth of the world’s population as well as one-sixth of the land area of the world’s largest urban areas are located in coastal zones less than ten meters above sea level.” These numbers dwarf the numbers of refugees now moving west in Europe, with enormous implications for geopolitical instability.

From the viewpoint of national security, climate change ought to rank near the top among America’s enemies. Yet, just when we should be ramping up that battle, this administration is rejecting the advice of its own military and intelligence advisors.