The number of cars on the world's roads surpassed one billion last year, according to a study that has spurred debate on what the rapidly-growing car population will mean for the world's economy and environment.

According to a report from Ward's Auto released last week, the global number of cars exceeded 1.015 billion in 2010, jumping from from 980 million the year before.

Not surprisingly, China led the way in vehicle growth, with the number of cars on Chinese roads increasing by 27.5 per cent, amounting to half the entire global growth.

That gives China the world's second largest car population, with 78 million vehicles. But the United States still constitutes by far the largest vehicle population in the world, with 239.8 million cars, the Ward's study reported.

In fact, China would have to increase the number of cars on its roads nearly sixteen-fold to equal the number of cars in the U.S. on a per capita basis. Ward's reports that there are 1.3 people for every car in the U.S., while in China there are 6.75 people per vehicle.

If China were to have as many cars per capita as the U.S., its fleet alone would amount to approximately one billion cars.

But while China's car population has been exploding, the U.S. has seen a less than one per cent increase in its vehicle population, roughly in line with most developed economies.

Earlier this year, the OECD's International Transport Forum forecast that the number of cars worldwide would reach 2.5 billion by 2050.

According to a seminar from Daniel Sperling at UC Davis' Institute of Transportation, a vehicle population of 2 billion would require the world to produce at least 120 million barrels of oil per day, up from about 87 million today. Given the slow depletion of conventional oil sources and the gradual move towards more expensive alternative sources such as the Alberta oil sands, it's not clear the world could develop such a large capacity to produce oil.

Transportation "currently accounts for 23 percent of the world's greenhouse-gas emissions," Brad Plumer writes at the Washington Post. "And most of that unconventional oil is significantly dirtier, from a CO2 perspective, than the traditional stuff. If people in the developing world keep buying vehicles ... then simple upgrades in fuel-efficiency alone aren't going to be enough to stop a steady uptick in global temperatures."

In an analysis published two years ago, Sperling noted that while "Beijing alone now adds nearly 1,500 cars to its roads every day," China's rapidly evolving economy makes the country ideally suited to lead the way in developing alternative energy vehicles.

Calling the country a "hotbed of innovation" that is "well positioned to respond to internal demands and international initiatives," Sperling pointed out that China is working on small electric cars; is imposing "aggressive" fuel efficiency standards; and is developing innovative public transit systems.

"What China can do, with its massive size and economy, is foster these ideas until they are fully developed and then launch them abroad," Sperling and co-author Deborah Gordon wrote.

Yet China, along with the rapidly growing economies of India and Brazil, are leading the world in increased demand for cars. And these countries often express resentment when they perceive efforts to curb unsustainable growth as being unfriendly to their development.

At this year's International Transport Forum, European speakers urged a renaissance in the use of bicycles as an alternative to cars. But representatives from China and India pointed out that their populations are currently in the process of shedding their bicycles in favour of more sophisticated transportation.

"The bike is better to get around in Beijing, but bicycle use is dropping fast due to poor air quality and the danger from car traffic," Tongji University professor Pan Haixiao said.

"Cycling is a miniscule thing," B.K. Chaturvedi of India's Planning Commission said. "That's not the future."