Car greenhouse gas emissions underestimated by a quarter

Carbon dioxide emissions from cars in Europe could be at least 25% higher than figures predicted by the International Energy Agency in its forthcoming annual report.

True MPG tests by What Car?, designed to give car buyers a better idea of their car’s fuel economy, measure the amount of CO2 emitted from the exhaust pipe in order to calculate MPG. Analysis of emissions from more than 600 car models on sale in Europe since 2012 has revealed that, on average, CO2 exceed the official EU figures by 25%. That equates to an extra 175 million tonnes of CO2, making the European annual total around 875 million tonnes.

In fact the difference between the official figures and the real-world numbers is growing each year; What Car?’s tests last year uncovered a 28% gap, while results for 2015 are currently more than 30% higher.

The EU figures are generated from the New European Driving Cycle (NEDC) test, which is carried out on a rolling road. Each session covers seven miles and lasts 20 minutes, and the car is tested only briefly at 75mph. What Car?’s tests are conducted on suburban routes, A-roads and motorways in south-west London for longer distances.

"While our tests show that modern cars are drinking less fuel and emitting less CO2, it’s disappointing that motorists are still being misled by the official figures," said What Car? editor Jim Holder.

"We launched True MPG in 2012 to give drivers a better idea of their car’s economy. We’re proud of what we’ve done in the three years we’ve been running these tests, but at the same time we’re all too aware that the vast majority of the cars on sale in the UK today aren’t as green as their makers claim."

The growing disparity between cars’ official CO2 emissions and the actual emissions is in part because of a rise in the number of hybrid cars on our roads. Many of these models can run on electric power for around 30 miles before the petrol engine has to fire up. In the NEDC tests, this means the electric motor is doing most of the work most of the time, which results in some astonishing figures.

Take the Mitsubishi Outlander PHEV GX3h, a petrol-electric plug-in hybrid SUV. Its official average economy figure is 148mpg and CO2 is 44g/km. Yet the True MPG is 39.2 and measured CO2 is 172g/km. The official figures mean annual road tax (VED) is free and a company car driver paying BIK at the 40% rate has a bill of £55 a month. Take the real-world figures into account, though, and VED should be £205 a year and company car tax becomes much less palatable, at £322 a month.

Then there’s the Porsche Panamera Hybrid. Officially it emits 71g/km of CO2 (free VED and company car tax bills of £253 a month). In reality, its 220g/km emissions mean annual VED should really cost you £290 and your tax bill will be an eye-watering £1042 per month.

Even the Volvo V60 Plug-In Hybrid, which promises to be a tree hugger’s dream with ultra-low emissions of 48g/km and monthly tax bills of £83, turns out to be a damp squib. Its real-world 185g/km emissions are nearly four times what we’re led to believe and you should really be paying £533 a month.

"It’s clear that the NEDC needs to be overhauled, and fast," said Jim Holder. "Car manufacturers want to delay any changes for another five years, but we want to see real-world testing implemented within two. That’s the only way car buyers can be assured that their future purchase’s emissions and economy will tally with the official figures."