A staggering $20 billion dollars a year is what the US military is spending on air conditioning in Iraq and Afghanistan: enough to give every man, woman and child in those countries $333 each.

The US military forks out a whopping $20.2billion a year on keeping troops in Iraq and Afghanistan cool, it has emerged.

The alarming figure is more than Nasa's entire annual budget and trumps the amount the G-8 has pledged to aid Egypt and Tunisia. It's even more than the clean up cost of BPs Gulf oil spill.

Why?

An air conditioning unit at a remote Afghanistan outpost takes a gallon of fuel, which soon goes in the searing 125degree heat. This has to be shipped into Karachi, then driven 800 miles over 18 days to the war-torn country on atrociously bad roads.

'And you've got risks that are associated with moving the fuel almost every mile of the way,' Steven Anderson, a retired brigadier general who served as General David Patreaus' chief logistician in Iraq, told National Public Radio (NPR).

Fuel convoys remain key targets for attack, and according to Anderson, more than 1,000 troops have died while delivering vital supplies.

For Anderson the military would save money by going green. He claims experiments with polyurethane foam insulation tents in Iraq cut energy use by a staggering 92 per cent, taking 11,000 fuel convoys off the road.

But getting the top commanders to embrace change has been hard.

'People look at it and say "It's not my lane. We don't need to tie the operational commanders' hands" - things like this,' he said. 'A simple policy signed by the secretary of defence - a one or two-page memo, saying we will no longer build anything other than energy-efficient structures in Iraq and Afghanistan would have a profound impact.'

It was thought President Obama's decision to bring 30,000 American troops home soon would act as a relief on the coffers. But according to experts the savings made by the withdrawal do not equal the $30billion cost of putting the soilders there in the first place.

'What history has told us is that you don't see a proportional decrease in spending based on the number of troops when you draw them down,' Chris Hellman, a senior research analyst at the National Priorities Project, said.

'In Afghanistan that's going to be particularly true because it's a very difficult and austere environment in which to operate.'

The infrastructure being built in Iraq is the main expense, according to American University professor Gordon Adams. 'We're building big bases,' the costs of which are 'sunk' costs, he said.

'We're seeing this in Iraq. We're turning over to the Iraqis - mostly either for a small penny or for free - the infrastructure that we built in Iraq. But we won't see back any money from that infrastructure.

The Obama administration has also requested $13billion to train and equip Afghan security forces in the next year.

But Afghan president Hamid Karzai also hinted a couple of years ago that Afghanistan would be in no position to support its own forces 15 even 20 years from now. It's likely the US will pick up that bill as well.