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# 2.2 Transport’s carbon dioxide emissions

There is a second major issue: the emission of ‘greenhouse’ gases which contribute to climate change. These are mainly carbon dioxide (CO2) from the combustion of fossil fuels, although with small contributions from nitrous oxide, a minor component of NOx and methane, a product of incomplete fuel combustion.

Globally, in 2022, transport contributed over 20% of CO2 emissions from the burning of fossil fuels (IEA, 2024).

In the UK, national domestic CO2 emissions (i.e. those emitted within the UK) have fallen, but as shown in Figure 3, most of the reduction between 1990 and 2018 was in electricity generation. Despite tightening vehicle fuel efficiency standards over this time period, there was almost no change in overall transport emissions. In 1990, transport CO2 emissions only made up about a fifth of total UK emissions. This proportion had risen to a third in 2018.

Figure 3: UK domestic CO2 emissions by sector, 1990–2018

In 2018, greenhouse gas emissions from cars and taxis made up over a half of the UK domestic total (see Figure 4). Although domestic aviation and shipping only made up 6% of the total, there were a further 42 million tonnes of international emissions (shown in black) produced by aircraft and ships which refuel in the UK.

Figure 4: Greenhouse gas emissions by mode of transport (millions of tonnes), UK - 2019

The UK Committee on Climate Change, which advises the government, has been most insistent that UK policies should address both domestic and international transport emissions.

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