BY THE 1950s traffic in California had become so heavy that anti-smog demonstrators took to the streets. China’s cities have now reached a similar stage, minus the street protests, and local and national governments are increasingly following American and European regulators in imposing limits on emissions by new cars of nitrogen oxides (NOX), hydrocarbons and fine soot particles. China is also getting more concerned about global warming and pollution, and has started to require manufacturers steadily to reduce the carbon dioxide (CO2) emissions of the vehicles they make.

Cars the world over will become appreciably cleaner in the coming years. The European Union is the strictest master. Under its “Euro 6” standards, due to come into force next year, diesel cars’ NOX emissions will have to be 84% below the limits set when it started regulating them in 2000, and their soot output must be 96% below the initial limits set in 1992. Earlier this year Beijing, in response to an episode of appalling air pollution, introduced new limits similar to the current EU ones, which it plans to tighten further in 2016.

The EU is also leading the way in cutting CO2 emissions, ahead of Japan, China and America (see chart 4). Carmakers know full well that they will have to keep investing heavily in low-carbon technology. Average CO2 emissions are due to come down from 130g per km now to 95g per km in 2020, and plans are already being drawn up for even tougher limits in 2025, of perhaps 70g. Bosch, a maker of sophisticated fuel-injection systems and other efficiency-boosting devices, has argued that such strict limits are perfectly achievable with petrol and diesel engines, even before looking to hybrids and other low-carbon powertrains.

Yet however ambitious the limits on new cars, most of the pollution and planet-warming gases come from older models. Michel Gardel, a spokesman on environmental affairs at Toyota, says that in France 80% of the pollution from diesel vehicles comes from 20% of the country’s diesel fleet, especially those made before 2000. Another round of “cash for clunkers” subsidies for trading in smoky old bangers would help clear the roads, but governments in most countries do not have any money for such largesse just now.

Some carmakers try harder than others to be green. At the Geneva motor show in March Volkswagen unveiled the XL1, an aerodynamically shaped plug-in hybrid with CO2 emissions of just 21g per km which will go into production, albeit in small quantities. In a study last year by Interbrand of the world’s “greenest brands”, as measured by both performance and public perception, three of the top four were carmakers: Toyota (first), Honda (third) and VW (fourth). The odd one out was Johnson & Johnson, a medical firm, which came second.

Besides making their models cleaner to run, many carmakers are also trying to reduce the environmental impact of manufacturing them. Toyota has drastically cut the amount of rubbish its American factories send to landfill and Ford recently announced plans to do likewise. Ford is also working on replacing plastic parts and foam seat-stuffing made from petrochemicals with alternatives made from plant materials.

Having been depicted as environmental villains since the 1950s, cars and their makers may soon be able to move out of the spotlight. “Cars have cleaned up their energy-usage act a lot,” says John Leech of KPMG, a consultancy, “and there will be a lot more talk and focus over the next five years about houses and industry…rather than cars not being very green.”