Some statistics are so huge they defy comprehension. When it comes to grasping the trillions of dollars of the US national debt, the mind cannot compute. But occasionally a number comes up which is so striking that it sticks in the brain.
One such number is the cost of the US military providing air conditioning for its troops in Iraq and Afghanistan. A minor expenditure, you would expect, but it comes out at $20 billion (Dh73.5 billion) a year. This staggering sum is more than the total budget of Nasa, the US space agency.
This figure has been worked out by Brigadier General Steve Anderson, who until his retirement was responsible for logistics in these war zones. By the time fuel reaches the US bases dotted around Afghanistan, it costs $8 to $12 a litre, 10 times the pump price in America.
Looking at the terrain, it is not so surprising: fuel has to be trucked from the Pakistani port of Karachi for 1,300 kilometres to Kandahar or Bagram, a journey of 18 days, then transferred to smaller tankers to drive over "improved goat paths" to the bases.
The costs, which the Pentagon disputes, include paying and protecting the contractors who guard the convoys against ambush, and the medical teams to treat their wounds and to evacuate the dead. In terms of human cost, 1,000 Americans and 150 Britons have died delivering fuel.
It is hot in Afghanistan, and the soldiers live in uninsulated tents where the air conditioning struggles to keep the temperature below 30°C.
Looking at US attempts to bring their own climate, no expense spared, to one of the most isolated parts of the world, one cannot fail to be reminded of Britain's experience in the First Anglo-Afghan War of 1839-42. The fighting force was outnumbered by a vast baggage train and thousands of camp followers so that the officers could live in comfort, dining with silver cutlery. That war ended in defeat, with the British column retreating from Kabul being massacred almost to the last man.
Gen Anderson does not make that grim comparison, but he does berate the Pentagon for failing to get a grip on its profligate energy use over the past nine years. Every delivery effectively stops the counterinsurgency campaign for a couple of days while soldiers are deployed to protect the convoy. "There is a direct relationship between energy efficiency and military effectiveness," he says.
The general has a reason for going public with these calculations. Since leaving the army he has joined the private sector and is promoting energy-efficient solutions, such as spray-on insulation for tents, which would cut fuel consumption. The Pentagon now recognises the need for this.
The cost to the US budget, however, is not the key issue, even though US public opinion is being primed to believe that money saved in Afghanistan will be spent at home. "Over the last decade we have spent a trillion dollars on war," President Barack Obama has said. "Now we must invest in America's greatest resource - our people."
This is less than honest. There are good reasons for ending the war, but that air conditioning money is not going straight into the pockets of the American poor. Given that the annual US deficit is 14 times the cost of the Afghan campaign, ending the war will not magically transform the federal finances.
The real issue is elsewhere. It is the total disconnect between the amount the US spends and the enemy that it is fighting. A new report by researchers at Brown University suggests that the final bill for the decade of the "war on terror" launched by George W Bush will come out between $3.7 and $4.4 trillion.
This figure is way beyond the money allocated by Congress, as it includes the cost of looking after the injured, the cost of the "empire of fear" at home to monitor potential terrorists, and the interest payable on the sums borrowed abroad to fund the wars, since they have been fought on credit.
Thus the total sum is likely to exceed the cost of fighting the Second World War, put by the congressional Budget Office at $4.1 trillion, in today's money.
In that conflict, the US was fighting some of the most technically and militarily advanced powers in the world - Germany and Japan. As a war between near equals, it led to a kind of peace. Today's conflict pits the might of America against an enemy in a country with no infrastructure and practically no modern economy.
The economic mismatch has bred an arrogance in the US about the possibility of defeating the Taliban. But that is not the worst of it. Inevitably the tide of dollars sloshing around Afghanistan undermines the government of President Hamid Karzai, the man the West is relying on to stabilise the country.
Another statistic underscores this. One of the smaller items in the Pentagon budget is the Commanders' Emergency Response Program, small sums of money which officers can spend at will to help the Afghan people. Its budget is about $750 million a year. This is chicken feed to the Pentagon, but it just happens to be about the same as the total revenue of the Afghan state which it raises itself (as opposed to handouts from abroad).
Not surprisingly, well-connected Afghans have been siphoning off as much money as they can, from aid projects, from security contracts and drugs, and sending it abroad. Why should the Afghan elite take responsibility for their country? Let Uncle Sam pay.
According to customs figures, more cash is taken out of the country each year than the government raises in revenue. And this is only the legal transfers. The sums that leave the country illegally can only be guessed at.
Great amounts of money are needed to win wars. But the truth is that generous military budgets present their own dangers. They have led the US astray from the original task of countering the terrorism threat of September 11. A tighter rein on military spending might have allowed wiser heads to propose a strategy more likely to succeed. Instead, the prestige of the US is now linked to the outcome of a war that no amount of dollars can win.