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What are CO2 emissions?

  • Why is it important to know about emissions?
  • How do they affect you?
  • CO2 emissions explained.

Written by Seth Walton Published: 28 July 2017 Updated: 22 August 2023

Carbon dioxide – widely known by its chemical formula, CO2 – is one of the gases produced when motor fuel ignites in an internal combustion engine. CO2 emissions have come under increased scrutiny over the last two decades or so for the role they play in climate change and global warming as a greenhouse gas. In response, the motoring industry is turning to electric cars to reduce emissions.

It’s now near-universally accepted that lowering your carbon footprint – that is, the amount of carbon dioxide released into the atmosphere as a result of your activities – is beneficial for the planet and global human health. Car manufacturers are striving to reduce the level of carbon dioxide their cars produce by electrifying their fleets, as the 2030 ban on internal combustion engines looms. But why are they so important?

On this page, we’ll explore why CO2 emissions are important and why they are shaping the future of the automotive industry.

Where do CO2 emissions come from?

Many major industries produce high levels of CO2, but since the advent of the combustion engine, cars have contributed toward global output. When fuel burns in an engine, the same chemical reaction that creates the explosions within a cylinder also combines carbon with oxygen in the air to produce carbon dioxide – CO2.

Gasses coming out the back of a car's exhaust
Cars with low emissions could save you money on your road tax.

The gas is then channelled through the exhaust manifold, out the back of the car and into the atmosphere.

Why are CO2 emissions important?

The subject of CO2 emissions is now graver than ever as destructive weather events around the world attributed to global warming are becoming more frequent. As both car manufacturers and car buyers aim to lower their carbon footprints, buying a low-CO2 car has become more of a priority for consumers.

Can I save money by running a low-emitting car?

As an incentive to buy low-emitting cars, the amount of CO2 produced will determine how much road tax you pay, both as a personal user and a company car driver. The lower the emissions, the lower the road tax. It’s measured in grams per kilometre – written as ‘g/km’ in car brochures and technical specs – and is the average amount of CO2 emitted from the car’s exhaust per kilometre travelled.

Air pollution in a built up urban area
CO2 emissions from cars significantly contribute towards urban air pollution.

Generally, the lower the CO2 rating, the better the fuel economy, too. Electric cars have zero emissions, while plug-in hybrids (PHEVs) tend to emit much less carbon dioxide than traditional petrol or diesel cars as power is delivered from the engine and an electric motor. For a full deep dive into the costs of charging an EV, check out our page on how much it costs to charge an electric car.

If you’re a business driver, CO2 emissions have an impact on how BIK tax you pay. Check our full guide to BIK tax for more info.