BioEd Online

An economic assessment predicts that the number of private cars on the world's roads will skyrocket from today's figure of just over 600 million to between 1.4 and 2.7 billion by 2050, doubling or quadrupling their carbon dioxide emissions.

"That's quite a lot, just for personal pleasure," says Ina Meyer from the Austrian Institute of Economic Research, who presented her results at the Earth System Science Partnership meeting in Beijing on 11 November.

Transport is a prime user of fossil fuel today, and is expected to continue to be so in the future. Whereas water and sunlight can power electricity plants, cars continue to be best suited to easily transported petroleum.

And people continue to be devoted to cars, a passion that is now catching on in Asia. Carbon dioxide emissions from all forms of transport are growing in Asia; in China this growth rate is 6.4% a year twice as fast as total global emissions (see ' Carbon tally shows growing global problem'). In most Asian countries, Meyer adds, the proportion of petroleum products going towards cars rather than some other energy use is also creeping upwards.

The numbers, which Meyer cranked out for her PhD and have now been submitted to the journal Energy Policy, are a stark reminder of the need to develop alternative transport energy sources.

"The automobile manufacturers have a responsibility to decarbonize," says Meyer.

Number crunch

To arrive at the numbers, Meyer first made the common economical-modelling assumption that people's behaviour will remain roughly the same. So in each country people will continue to spend the same proportion of their salary on a car. Population and gross domestic product (GDP) projections then predict a stock of more than 1.4 billion cars on the road by 2050.

Assuming a bettering in fuel efficiency of 1 litre per 200 kilometres every 20 years (as has happened so far), that means emissions of more than 4 gigatonnes of carbon dioxide a year by 2050, compared with today's annual 2 gigatonnes.

But, says Meyer, as a rule people actually start to spend a larger proportion of their earnings on a car as they get richer, so this is probably an underestimate.

She then instead assumed that every country would follow the same car-buying behaviour as the United States, with people buying more and more until reaching a saturation limit of about 0.6 cars per person. This leads to an estimate of 2.7 billion cars and 8 gigatonnes of carbon dioxide by 2050.

This is probably an overestimate, admits Meyer, since most countries don't have the wide-open spaces of America that make a car a necessary luxury, but instead face an overburden of traffic jams that comes with high-density living. "The truth is probably somewhere in between," she says.

Fortunately, the current research and development into biofuels, and electric and hydrogen cars, makes Meyer's emissions predictions look pessimistic. But it is urgent that such research continues, say environmental researchers in Beijing (where the main roads have more than 10 lanes of traffic and the city's iconic bicycle stock has declined dramatically).

"We need a portfolio of technologies," says Jürgen Kropp at the Potsdam Institute for Climate Impact Research in Germany.

"And you have to have good public transport," adds Meyer. She herself rides a bicycle. "And sometimes I fly to Asia."

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