Open Menu

    Car CO2 emissions – the ultimate guide

    Do you know what the CO2 emissions are for your car? If not, do you know where you can find the information?

    Do you know your WLTP from your RDE or what the difference is between CO2 emissions and Euro 6 Standards emissions? Do you know if your car is London ULEZ compliant?

    If not, then don’t worry. With so many changes over the last few years, things have become confusing, especially surrounding what all the different emissions ratings are for.

    CO2 rules and laws
    Countries across the globe have pledged to reduce CO2 emissions

    Our ultimate guide covers everything you need to know about car CO2 emissions, so you can understand how much car tax you might have to pay and how you might reduce the emissions on your current car.

    CO2 car emissions explained:

    1. What are CO2 emissions and why do they matter?
    2. CO2 emissions legislation in the EU and UK
    3. What is Euro 6?
    4. How is a car tested for CO2 emissions?
    5. CO2 emissions tables for car tax
    6. Where do I find the CO2 emissions rating for my car?
    7. How can I reduce my car’s CO2 emissions?

    What are CO2 emissions and why do they matter?

    For millions of years, carbon dioxide (CO2) emissions have been produced naturally on the earth by decomposition, ocean release, and respiration. These natural levels are usually kept in balance by the ecosystem of the planet as CO2 is reabsorbed in a natural cycle.

    However, CO2 can also be produced through human intervention and the burning of fossil fuels for heating, industry, and transportation.

    This increase of man-made emissions has upset the natural balance to the point of causing possibly irreversible damage to the earth and its atmosphere, known as climate change.

    For this reason, collectively, worldwide countries have pledged to take action, part of this includes significantly reducing the CO2 emissions from cars and other vehicles.

    CO2 emissions legislation in the EU and UK

    Currently, transport is the highest contributor to emissions, responsible for around 33% of CO2 emissions in the UK, and 30% across Europe. In a bid to tackle this significant contribution, the European Commission and industry associations of carmakers agreed to reduce the emissions on any new cars built.

    • The first target in 2009 was to cut average car emissions to 140 g CO2/km.
    • In 2015, this target reduced to 130 g CO2/km
    • The goal for 2021 is for 95g CO2/km

    Carbon dioxide emissions are measured by weight, in grammes (g) and calculated by how much CO2 is emitted from the exhaust pipe per the distance driven, measured in kilometres (km). CO2 emission rates are usually displayed as (g/km).

    In a similar way to fridges being labelled with energy efficiency data, all new cars for sale now have to display a label showing the fuel consumption and CO2 emissions.

    The label should be on the car or nearby and anyone shopping for a car should look out for this and report it if it’s missing.

    Alongside tackling climate change, making the air we breathe safer from pollutants has also come under scrutiny and car emissions are also targeted under Euro 6 standards as part of the European Commission’s air quality directive.

    Euro 6 standards
    All new cars must meet Euro 6 emissions standards

    What is Euro 6?

    Exhaust gases from cars contribute to air pollution, especially in concentrated areas such as cities. In addition to CO2, cars also emit the following pollutants:

    • CO – carbon monoxide
    • NOX – oxides of nitrogen is the total amount of nitrogen oxide (NO2) and nitric oxide (NO)
    • PM – particulate matter (soot from diesel cars)
    • HC – hydrocarbons

    The collective emissions of all these air pollutants were targeted by the EU with a limit set in 1993 known as Euro 1. Over time there have been subsequent revisions to these limits and all new cars must meet the current revision of Euro 6 standards.

    Air pollutant emissions data is displayed on cars for sale alongside the CO2 data, but unlike the CO2 data, it should not be used for direct comparison between different cars. The numbers are only used as a measure to meet the Euro 6 limits.

    What will happen to legislation after Brexit?

    Currently, the UK must follow the EU legislation set out in 2009 (EC 443/2009) and then in 2014 (EU 510/2011), the European Union Ambient Air Quality Directive (2008/50/EC) and Euro 6 standards (459/2012/EC).

    Following Brexit, the UK will no longer be held under EU regulation but it is anticipated that the standing EU emissions regulations will be brought into UK legislation.

    Drivers can expect that the emissions levels set in the EU will continue after we have left the Union.

    At the end of 2020, it was announced by the British government that, as part of a proposed ‘green industrial revolution’, there would be an outright ban on the sale of new petrol and diesel cars in the UK from 2035. However, some hybrid cars would still be allowed.

    How is a car tested for CO2 emissions?

    When a car or vehicle burns petrol or diesel, CO2 is emitted from the exhaust pipe and these emissions are measured during the testing of new car models and during the annual MOT test.

    Previous emissions testing for new cars was done through the New European Driving Cycle (NEDC) rating, which was based on theoretical driving calculations.

    After the emissions testing scandals of VW and others, stricter standards were set. On 1st September 2018, the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) was introduced to measure emissions more accurately.

    The upgrade of the testing system has caused considerable disruption in the car industry due to downgraded results for most car model ratings with lower fuel economy and higher emissions reported.

    Major changes in testing involve cars being scrutinised over a longer distance, at higher speeds and with in different driving conditions for a more accurate representation of driving.

    Faster acceleration, sharper braking, roof racks, and alloy wheels are all taken into consideration.

    Cars are selected at random from the manufacturing line to ensure they can’t be ‘prepared’ for testing.

    Just to confuse things even more, Real Driving testing (RDE) is also being used to supplement the laboratory-based WLTP results. The vehicle is tested on a public road to gain the best real-life emissions results.

    At this moment, only NOx is measured by RDE until more accuracy can be assured in the testing.

    It’s not just new cars that are tested for their levels of emissions. Emissions are tested annually during the MOT test and your car will fail if emissions are higher than the standard set for the age of your vehicle.

    It’s worth noting that diesel cars had a new rule introduced on 20th May 2018 for the MOT test. The standard for the car will be used from the listing on the manufacturer’s plate. If the car emissions are not listed on the plate, then the car is tested to the default level for its age.

    Roadside checks can also be made to measure emissions with an allowance of 10 days to fix high emissions if your car fails. If the emissions are exceptionally high, then you will not be able to use the vehicle until it is fixed.

    CO2 tax
    Cars valued over £40,000 now have to pay an extra £320 a year for car tax

    CO2 emissions tables for car tax

    Since 2001, car tax has been charged based on a specific model’s CO2 emissions and not engine size. In the last few years, this has become a little more complicated as rates now vary depending on when the car was registered:

    Cars registered before 1st March 2001:

    • The tax rate is based on the engine size, see here

    Cars registered between 1st March 2001 and 31st March 2017:

    • The tax rate is based on fuel type and CO2 emissions, see here

    Cars registered after 1st April 2017:

    • When the car is registered, you pay a fee for the first year depending on the emissions set for the vehicle, see here
    • After 12 months, you pay a fee based on the fuel type of the car with electric cars exempt from payment, see here
    • For a car with a value over £40,000 you have to pay an extra £320 for five years (after the first year)

    Cars registered before 8th January 1979:

    • Are exempt from having to pay a fee (but only for private vehicles)

    Where do I find the CO2 emissions rating for my car?

    If you look in your V5C registration certificate for your car, the emissions rating is listed there. Or, you can find the fuel consumption and emissions information for a new or used car on the government certificate agency website.

    Drive smart
    Making changes to how you drive will reduce your emissions

    How can I reduce my car’s CO2 emissions?

    Whatever the official emissions ratings of your car, reducing your CO2 emissions will benefit you and your car. You’ll get better performance, better fuel MPG and it will help the environment.

    Below are Motorway’s top suggestions to put into action:

    Selling your car?

    Read about everything you need to know about how to sell your car with more guides here. There’s a lot to learn as Clean Air Zones and emissions standards in the UK change in the run up to 2035.

    Sell your car the Motorway way

    Find your best offer from 5,000+ dealers