Until the talks, the US military was exempt from reporting its total emissions after getting a congressional opt-out to the Kyoto Protocol, which itself was never ratified by Congress. The new COP21 agreement could reverse that, but the details of the deal don't go as far as forcing any emissions reductions, and it's entirely possible that Uncle Sam might get yet another exemption.
"Lets face it, vast swathes of our military are big carbon emitters – tanks, Jeeps, humvees, jet planes – and of course much of our navy is not nuclear-powered, so [the Paris agreement] could be used as a Trojan horse," Steven Groves, a senior research fellow at the US-based Heritage Foundation told The Guardian. "This might be a good opportunity for people concerned with national security to go to congress and get some type of legislative exemption in the same way as was done during the Kyoto time period."
While the idea of reporting carbon emissions might irk some in the military-industrial complex, the reality is that the US military has made concerted efforts at shrinking its carbon footprint. Uncle Sam isn't doing this out of the goodness of his heart, though – cutting carbon emissions would likely mean reducing the military's reliance on fossil fuels, a move that could not only save American lives but remove (or at least lower) a serious logistical hurdle for planners.
In many ways, the military has already taken to embracing this movement. The Navy's nuclear-powered carriers and submarines don't rely on any fossil fuel, and in 2014, it made headlines after announcing plans to develop biofuels for its ships and aircraft. Such a development would likely spread like wildfire to the Army, Air Force, and Marines, and make a serious dent in whatever the military's carbon emissions end up being.