When it comes to climate change, the Department of Defense has historically focused on preparation rather than prevention.

Last week, the Democratic presidential candidate Elizabeth Warren released a climate proposal focused on the military, calling for the Department of Defense (DOD) to decrease emissions while increasing the military's readiness for climate change. It's the latest addition to a series of climate proposals from the 2020 presidential hopeful, who has also released plans to ban offshore drilling and up renewable energy generation.

"We don't have to choose between a green military and an effective one," Warren wrote in a Medium post outlining the Defense Climate Resiliency and Readiness Act.

The Pentagon has long-recognized climate change as a threat to national security, although the lens through which the DOD has historically viewed the issue has been one of preparation and resiliency, rather than prevention and reduction of emissions.

"The DOD has been paying attention to this issue for several administrations," says John Conger, the director of the Center for Climate and Security, a non-partisan think tank that evaluates the threat of climate change. According to Conger, the DOD's focus on climate change falls into three categories: how it currently affects the military's ability to do its job; how it will change what its job is in the future; and how it affects geopolitical stability.

Extreme weather is already affecting the military's readiness today. "The DOD doesn't use live fire munitions when there's a drought out West, because it could start a wildfire," says Conger, noting that drought conditions are expected to become more common in that region. Sea level rise and severe storms can damage infrastructure and eat up resources. "Nuisance flooding is only an appropriate term when you don't have impacts and, frankly, when you flood portions of the base you have operational impacts," he says. "The main road into Norfolk Naval Station, which is the largest Navy base in the world, floods several times a year, and within the next 20 years or so, they're expecting it to flood daily."

Warren noted that hurricanes left Camp Lejeune in North Carolina and Tyndall Air Force Base in Florida with billions of dollars in damages each last year; extreme flooding in Nebraska left the Offutt Air Force Base with nearly half a billion dollars worth of damages.

Climate change is also changing the military's missions and priority. As the polar ice caps melt, new trade routes will open up and oil extractions could increase, as could fishing pressure. Activity in the region is expected to surge. "So the Navy has a whole new ocean to patrol as the ice recedes," Conger says.

For at least a decade the DOD has been looking ahead to how food and water scarcity could lead to economic crises that drive mass migrations and seed conflict. "Climate change often isn't the principal cause of instability, but it is an aggravator of instability," Conger says.

Under the Obama administration, the urgency with which the DOD was developing and adopting renewable energy technologies increased. Between 2011 and 2015, the number of renewable energy projects the military invested in tripled, and the amount of renewable energy generation doubled. Still, the United States military remains one of the planet's biggest polluters, and is the largest institutional user of fossil fuels, consuming more than 100 million barrels of oil every year.

"We have the most capable military in the world. It's also the single largest government consumer of energy, and it's dependent on fossil fuels," Warren wrote. "The Pentagon spends about $4 billion a year to power its bases at fixed locations and consumes tens of billions of barrels of fuel per year."

Warren's plan pushes the DOD's adoption of renewable technologies further: She calls for the military to reach net zero emissions on non-combat bases and infrastructure by 2030. It's an ambitious goal, but critics note the "net-zero" language leaves room for carbon offsets, which allow big polluters to keep emitting while purchasing emissions reductions from elsewhere.

Warren's proposal also requires the Pentagon to release an annual report evaluating every military base individually, "using real scientific methodology," for climate vulnerabilities. Individualized reviews are "something that [the DOD] probably ought to do," Conger says. "We've written about that in the past, at the Center for Climate Insecurity, suggesting that the DOD needs to develop what we characterized as 'military installation resilience plans' for each individual base, where they actually think through the threats at the base, because the threats are going to be different at every base, the vulnerabilities are going to be different at every base."

The most original piece of Warren's proposal in the treatment of military contractors. The DOD issues hundreds of billions of dollars worth of work to contractors every year. Under the act, contractors that have yet to reach zero emissions would "pay a small fee," equivalent to 1 percent of their contract. Warren said she would invest the money in climate-resilient infrastructure for the military.

Her plan would also renew focus on advancing renewable technologies, investing billions in a 10-year research and development program focused on micro-grids and energy storage.

Conger won't comment on the Warren campaign's proposal specifically, but he notes that, even under President Barack Obama, when the military embraced a conversation about emissions reductions and expanding renewables, DOD officials' "perspective tended to be 'I'll do those things, but it has to be in the context of helping my mission,'" he says. And while the Trump administration has de-prioritized climate change, the military has continued to evaluate how it might affect its mission. "As you think about the swings of administrations, the military's been remarkably stable in its perspectives," he adds.

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