The average CO2 emissions of cars on UK roads has grown by 0.8g/km to 121.3g/km in the third quarter of 2017, compared with the same period in 2016.
The last quarter's rise in emissions has been put down to the increasingly negative rhetoric regarding diesels since the emissions scandal of late 2015, which has culminated in higher taxes for new diesels, thus putting buyers off diesel cars, which typically have lower CO2 outputs than their petrol counterparts.
Average CO2 figures fell by just under 61g/km between 2000 and 2016, and car makers have an EU deadline for their fleet averages to be 95g/km or below by 2021.
This then has to be reduced by a further 30%, to 66g/km, by 2030. This target has been criticised as being too aggressive by the European Automobile Manufacturers Association (ACEA).
The stringent new targets, as well as the tax penalties, are designed to accelerate the uptake, both in production and purchase, of low-emissions vehicles such as hybrids and EVs. Despite these being the fastest-growing area of the new car industry, the segment still remains tiny.
While select manufacturers are beginning their electrification strategies over the coming year, the majority of EV plans will come into full force in 2019, meaning that 2018's average CO2 figure is likely to follow 2017's suboptimal lead.
In the first 11 months of 2017, hybrid, electric and hydrogen vehicles represented 4.7% of all new car registrations, having grown by 34.6% over the same period in 2016.
The UK's fleet sector remains below the national average, at 111.6g/km, prompting British Vehicle Rental and Leasing Association boss Gerry Keaney to say: "We currently have a poorly designed tax environment that encourages people to make their own arrangements rather than choosing a company car. This is putting older, higher-polluting grey fleet vehicles (employee-owned but used for work) on our roads.
"To this, we can add the demonisation of diesels and continued uncertainty around air quality measures, which are nudging people towards petrol cars. The inevitable result is that CO2 levels are increasing."
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