Trident missile launch 2008 courtesy spacewar.com The military is the only sector of the economy where emissions of green-house gases (GHG) can be reduced by greater than 100%. This is because militarism is the only type of activity whose primary purpose is destruction.
When a road is bombed in Serbia, energy is used to rebuild it. Energy usage translates to the emission of GHG, primarily carbon dioxide (CO2). When a home is leveled in Afghanistan, reconstruction requires energy. Every hospital brought down and every person maimed in Iraq means CO2 emissions during the treatment of patients and construction of new treatment facilities.
Military production is unique. If it were halted, GHG emissions would be reduced by an amount equal to (a) GHG emitted from repairing what the military bombed, plus (b) GHG produced during its regular activities of building bases, using weapons and transporting troops and equipment.
Though the official figure for the military budget is $623 billion, the War Resistors League calculates total military-related spending at $1,118 billion by including NASA, Department of Energy nukes, vet benefits and interest on past military debts. Another $110 billion should be tacked on for extra spending on the war in Iraq.
The gross domestic product (GDP) is $13,246.6 billion.  Putting these together leads to an estimate that just under a tenth of the US economy is military-related spending: [$1,188B + $110B] / $13,246.6B = 9.80%
This only accounts for military sales to the Pentagon. Since US arms manufacturers are major providers for regimes throughout the world, military spending actually accounts for considerably more than 10% of the GDP.
Graphic by Harold Willens, updated 1990 by Canadian Physicians for the Prevention of Nuclear War, certified accurate by US Senate staff. The centre dot is all the explosives used in WW2, the surrounding dots the world nuclear arsenal. Those carried on one Poseidon sub are shown in the small circle upper left, in the circle lower left the 24 megatons (8 x WW2) on one Trident sub. Two squares (300 mt) will destroy all large and medium cities in the world.
Militarism may contribute more than any other 10% of the economy to oil depletion, creation of toxins and habitat destruction. Yet, the one area of the economy where a greater than 100% reduction in greenhouse gases is possible is the area least likely to be discussed in connection with climate change.
-- excerpt from Fitz, Production-side environmentalism
See also UN Secretary General, 18 Feb 09: "Progress in Disarmament Could Free Up Resources to Tackle Climate Change" and Patricia Hynes' 7 part series 2011 in Truthout "War and the Tragedy of the Commons".