Rupert Cornwell: The US stays cool, but is global warming the price?

What single device or person has done the most to make America what it is today? George Washington, Thomas Edison, the motorcar and the internet are all obvious contenders. My vote though would be for Willis Carrier. Never heard of him? He invented modern air conditioning, that's all.

The choice, I admit, is partly inspired by the current and seemingly endless heatwave here. June in DC was the hottest on record, and this month has been hotter still, with the temperature forecast to top 38C (100F) yesterday. Add in Washington's sapping summer humidity, and you understand why the Foreign Office once upon a time considered this city a diplomatic hardship post. But that was before 1902, when Carrier came up with a device to stop the sticky air from ruining the magazines produced at a print works in New York City.

Since then, America has been transformed by air conditioning. Without it, the huge migrations from the old industrial states of the midwest and north-east to the west and south would never have happened. Take, for instance, Phoenix, set in the baking Arizona desert where highs this month have hit 46C (116F) and night-time lows are in the mid to high 20s.

In 1940, when air conditioning was for most people a miracle to be experienced in movie theatres, just 65,000 people lived there. Then AC arrived as a standard, affordable feature of new homes, and Phoenix took wing. By 1960, the population had leapt to 440,000; today it is America's fifth largest city, heart of a metropolitan sprawl where 4.3 million people live and go about their business. They live in air conditioned suburban homes, work in glass air conditioned skyscrapers and drive ever longer distances between the two in cool and comfort.

The story's similar for places such as Los Angeles, Dallas, Houston and Miami, respectively the country's 2nd, 4th, 6th and 7th biggest metro areas. World cities all, but where would they be without the invention pioneered by Willis Carrier?

And the same goes for politics. Back in 1960, when only one in eight American homes had air conditioning, America's governments and prevailing ideologies were overwhelmingly drawn from the north-east, with its entrenched Democratic traditions matched by a moderate, somewhat paternalistic Republicanism. Then AC arrived – and not by coincidence the US underwent a Republican sea change.

But (with the exception of the elder George Bush) the party's leaders since the 1960s were no longer gentlemanly "country club" types from the north-east. Not only population but also the country's political centre of gravity shifted south- and west-ward. These regions produced a new breed of Republican who reflected their more rugged, individualistic ways. Yes, George W Bush went to Yale, but he was a creature of the torrid Texan plains. Ronald Reagan may have been born in Illinois, but California made him. Who knows, without air conditioning in the US, Communism might never have fallen and Iraq might never have been invaded.

But enough of speculation. Let us focus on the facts, and in environmental terms they are not pretty. By 1980, it was calculated, the US, with only 5 per cent of the world's population, accounted for more air conditioning than the rest of the planet put together. Today, the figures are even more staggering.

According to Stan Cox, author of the recent book Losing Our Cool: Uncomfortable Truths about Our Air-Conditioned World, AC for buildings and cars alone in the US generates the equivalent of half a billion tonnes of carbon dioxide annually, more than the total CO2 emissions of France, Brazil or Indonesia.

Obviously air con has been a boon for the economy; no longer do output and productivity slump as they once did during the summer, when factories shut and office workers were sent home. The north-eastern rustbelt may slowly be re-inventing itself, but places like Houston, Las Vegas and Dallas are now year-round dynamos of the national economy.

No less obviously, AC has made summers far more bearable and easier to organise. If it's 100F in the shade and a step outside is like walking into a sauna bath – no problem. Close the windows tight, adjust the AC, and you can turn July into January. Indeed, walk into any shopping mall in Miami or Phoenix right now, and you'll wish you'd brought an extra sweater.

Worse still, Cox argues, air conditioning increases demand for more air conditioning. On the roads, the ever-growing amount of poisonous exhaust spewed out by cars makes it even more essential for other drivers to roll up their windows and crank up the AC. More subtly, the more time we spend in air-conditioned environments, the less we are able to cope with the heat provided by mother nature. And so, humans being the resourceful species they are, the air-conditioned universe widens further.

But for how much longer? As the world gets hotter and global demand for energy continues to rise, air con will have to be brought into the broader climate change debate. Do you find alternative sources, or do you find a way of getting by with less? Or, as seems to be the case in Washington, do you simply do nothing?

The weather outside may be a portent of even hotter, more uncomfortable summers to come. But Congress last week more or less hauled up the white flag of surrender on a meaningful climate change bill, opposed most stridently by Republicans from the AC belt. It's too late now for a bill before November's mid-term elections. After them, new Republican majorities may render moot any talk of reform. But then again, what's the rush? The air con's wonderful on Capitol Hill.