Drivers in the UK are switching to more economical, less polluting cars. On average their vehicles pump out 140g/km of carbon dioxide from their exhausts, a figure that’s fallen by 4.3% in just a year.

That decrease is common to motorists across northern Europe and is propelled by the scrappage scheme that most countries operated, which encouraged drivers to swap old, more polluting cars for more efficient new ones. Many drivers also used the schemes to switch to smaller cars, further reducing emissions levels. In the UK, new road tax bands which favour lower emissions and a company car tax system slanted the same way have encouraged the downward trend.

But we still have some way to go to equal Japan, where the average per vehicle is 130.8g/km. At the other extreme, the average for the United States is a massive 255.6g/km per vehicle. And there's little sign of that figure dropping.

‘American consumers need to undergo a fundamental re-think of their vehicle buying preferences,’ said David Mitchell, a spokesman for JATO Americas, the company behind the research. ‘The blame can’t just lie with consumers, though,’ he continued. ‘The product offering in the US ds little to promote alternatives to the large capacity gasoline engines which dominate the market.’

The cost of unleaded is relatively low in the US and, as a result more than a third of new cars sold in the US manages less than 20mpg overall. In Japan and Europe, almost all new cars are more economical than that. European average emissions have reduced largely thanks to the increasing popularity of diesel cars. Almost half of all the fuel sold in Europe is now diesel, compared to just 1.7% in the US. There, petrol still holds sway, taking 81% of the market.

In Japan, sales of diesel fuel are tiny but that nation’s highly congested roads favour small, highly efficient petrol engines. Hybrid cars (which use petrol and electric engines together to reduce emissions and improve fuel economy) are also more popular in Japan than anywhere else – they account for one in 10 new car sales. In the US the figure is one in 50, where in Europe it is just one in 200.