What Are CO2 Emissions?

Carbon Dioxide, also known as CO2, is a gas in the Earth’s atmosphere.

Natural levels of CO2 emission are balanced out in the Earth’s ecosystem through processes such as trees and plants absorbing CO2 during photosynthesis.

However, in recent years we’ve increased the level of CO2 emissions through the excessive burning of fossil fuels, including in our cars with petrol and diesel. 

Globally the world is trying to reduce the amount of man-made emissions. In the UK around 33% of 2018’s CO2 emissions were produced by transport, which is why the government is committed to reducing the amount by putting a stop to the sale of new vehicles that are powered by traditional fuels. Click here for more information on this ban.


With numerous benefits in place for vehicles with lower emissions, when it comes to looking at a new lease the vehicle's emissions are an important consideration. 

How Are CO2 Emissions Measured?

CO2 is measured by its weight in grams.

For a vehicle’s CO2 emissions, the amount of CO2 emitted over a set distance is measured. This is usually done in grams per kilometre, so when you’re looking at cars you’ll see the value written as g/km.

The UK aims for all new vehicles to only produce 95g/km by the end of this year.

There are a few different ways that emissions are being measured at the minute, take a look at these below:


Up until the 6th of April 2020 the New European Driving Cycle (NEDC) rating of a car will be used to give the vehicle its CO2 emission rating.

This measurement is reached through a series of tests in the laboratory but has been criticised for not reflecting real life driving conditions, as the tests had not been updated in nearly 20 years, and most EU countries are now changing from NEDC to WLTP measurements.

WLTP Testing:

On the 6th of April the UK will switch their emission measurement from the previous NEDC to a new set of tests – the Worldwide Harmonized Light-Duty Vehicles Test Procedure (WLTP) tests.

These tests are designed to provide ratings that reflect driving conditions in the real word, and are run over a series of different driving cycles, for a longer time and more realistic driving temperatures.

To see a more extensive breakdown of the WLTP tests take a look at this blog.


 The Real Driving Emissions (RDE) test measures the pollutants from a vehicle whilst it is being driven on a road, rather than in laboratory conditions.

This test does not replace the NEDC or WLTP test but works along side them to provide you with additional data on a vehicle's emissions.

CO2 is not currently measured by RDE tests, but may be in the future. 

Euro 6:

The Euro 6 is a revision of the Euro 1, an EU target for vehicle emissions.

It measures the other emissions, apart from CO2, that a car produces. This includes: Carbon monoxide, nitric oxide, nitrogen oxide, hydrocarbons, and particulate matter like soot.

When you’re looking for your next lease car you don’t need to worry about this measurement, as this is only given to a car to show it is meeting the European standards.

After Brexit the UK is likely to keep the current standards but not accept new ones from the EU. Instead the UK government will continue to set their own goals and restrictions in line with more general CO2 and emission reduction targets.

MOT Testing

Vehicles are also tested for their emission levels at their MOTs.

If you are leasing, and your lease is for less than three years then you will not need to worry about this.

If your lease is for longer than three years your car will need a MOT. The emissions will be rated and if they are higher then they should be it could fail the MOT, but this is very rare on such a new vehicle.

Road Tax

If you are leasing a vehicle then you will not need to worry about the road tax as this is covered by the funder for the duration of your lease.

However, if you own the vehicle then the CO2 emissions will affect the road tax you pay.

Company Car Tax

If you are using a car provided to you by your employer, then you will have to pay company car tax.

This is in part based on the CO2 emissions produced by the vehicle. Our Guide to Company Car Tax explains in full how the emission rating is taken into account.

CO2 and Low Emission Zones

With us all becoming increasingly aware of the impact that vehicle emissions have more and more cities are putting into action plans to try and reduce the amount in their city centres.

A lot of cities are following London's lead and putting in place Low Emission Zones (LEZ) or Clean Air Zones (CAZ), where vehicles that do not meet the emission standards set out have to pay a charge.

If you are looking at a new lease vehicle and work in a city where there is a LEZ or CAZ area, then you might want to look at the criteria for these and pick a car where you won’t be charged a higher rate.


How Can I Reduce My CO2 Emissions?

There are a number of things you can try to reduce your CO2 emissions on your current vehicle, including:

  • Use better fuel
  • Add cleaning agent to the fuel tank every now and then
  • Change the oil and make sure you use the right grade
  • Change the air filter
  • Keep up to date with services
  • Check tyre pressure and keep at an optimum level
  • Turn the air conditioning off
  • Remove any roof and bike racks when not using
  • Don’t sit with the engine running
  • Drive with consideration and avoid hard accelerating

Alternatively, if you are looking for a new car then you might want to consider a hybrid or even a fully electric vehicle. Check out our top offers on these or have a look at our Guide to Electric Vehicles for more information on them.

If you have any questions about the CO2 emissions on a car you’re interested in, then please get in touch on 03302210000.

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