New cars emitting more CO2 than older models, warns Which?

The latest new cars are producing more carbon dioxide emissions than older models, according to new research by Which?

Test data from the consumer group found that the most recent petrol, diesel and hybrid cars are emitting an average of seven per cent more CO2 than cars from as recently as two year ago. However, it also found that they were emitting far lower amounts of other harmful pollutants, such as nitrous oxide and carbon monoxide.

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Which? examined data for every car it has tested since the start of 2017 - a total of 292 models - and found an average increase in CO2 of 10.5g/km from 151.6g/km to 162.1g/km. The rise in CO2 emissions was seen across almost all car classes and fuel types.

Rather than use official WLTP figures, the Which? analysis was based on its own in-house testing, which uses an additional tough motorway cycle, loads cars with 200kg of weight to simulate passengers, and switches the air con and radio to reflect real-world use.

While average CO2 emissions were up, the levels of NOx and CO were significantly lower than for older models (Photo: Shutterstock)

The analysis revealed that most cars which meet the latest emission regulations, Euro 6d-temp and Euro 6d emit more than those which met Euro 6b and Euro 6c, which lasted until 2017 and 2019 respectively.

Small petrol cars - in the supermini class - saw an average increase in CO2 emissions of 11.2 per cent (to 145.7g/km), while mid-size petrol SUVs - the class including the Nissan Qashqai, Ford Kuga and Renault Kadjar, rose by 20.4 per cent (to 189.8g/km). Large petrol-electric hybrids (Ford Mondeo/BMW 3 Series size) were the worst offenders, with an average increase of 31.7 per cent (to 117.4g/km).

Which?’s testers suggested that the continued increase in weight of cars is partly to blame for the increase in CO2 emissions. While manufacturers are increasingly using lightweight materials in new models' body construction, Which?’s test figures show an average 67kg increase (3.4 per cent) Euro 6d-temp/6d cars, compared with earlier models that meet Euro 6b/6c.

In general, new generations of a car are larger than their predecessors and often feature more technology, which contribute to their rising weight.

Which?’s lab experts also suggested that the technical and software modifications needed to reduce harmful emissions, such as NOX and CO, could have led to a rise in fuel consumption and, as a result, higher CO2 emissions.

Drop in NOx pollution

Their testing did find significant reductions in emissions linked to damaging human health. In petrol cars, carbon monoxide emissions have dropped by 40.6 per cent, on average. Across tested diesel vehicles, the decrease in NOx was an average of 84 per cent.

Lisa Barber, editor of Which? Magazine, said: “It is shocking to see our tests uncover increasing levels of carbon dioxide emissions for the latest cars that are being built and sold to UK consumers.

“Manufacturers must ensure that they are doing everything in their power to create cleaner vehicles that are fitter for our planet and its future.”