Overview of greenhouse gases
The GHG inventory covers the six direct greenhouse gases under the Kyoto Protocol:
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Hydrofluorocarbons (HFCs)
- Perfluorocarbons (PFCs)
- Sulphur hexafluoride (SF6)
These gases contribute directly to climate change owing to their positive radiative forcing effect. HFCs, PFCs and SF6 are collectively known as the 'F-gases'.
In general terms, the largest contributor to global warming is carbon dioxide which makes it the focus of many climate change initiatives. Methane and nitrous oxide contribute to a smaller proportion, typically <10%, and the contribution of f–gases is even smaller (in spite of their high Global Warming Potentials) at <5% of the total.
Also reported are four indirect greenhouse gases:
- Nitrogen oxides
- Carbon monoxide
- Non-methane volatile organic compounds (NMVOC)
- Sulphur dioxide
Nitrogen oxides, carbon monoxide and NMVOCs are included in the inventory because they can produce increases in tropospheric ozone concentrations and this increases radiative forcing (warming of the atmosphere). Sulphur dioxide is included because it contributes to aerosol formation which can either warm (through absorption of solar radiation on dark particles) or cool (from forming cloud droplets and reflecting radiation) the atmosphere.
Important sources and trends
The largest source is the combustion of fossil fuels in the energy sector, typically approximately 85% of total emissions. Emissions of CO2, CH4 and N2O arise from this sector. Energy sector emissions have declined since the base year of 1990, primarily due to fuel switching to less carbon–intensive energy sources (e.g. coal to gas in the power sector) and reduced energy intensity of the economy (e.g. declining iron and steel and metal production industries).
The second largest source of greenhouse gases in the UK is the agricultural sector at up to 10% of total emissions. Emissions from this sector arise for both CH4 and N2O. Since 1990, emissions from this sector have declined due to a reduction in livestock numbers, changes in the management of manure and restrictions in the use of synthetic fertiliser.
Industrial processes sector makes up the third largest source of greenhouse gases in the UK, contributing to up to 5% of the national total. Emissions of all six direct greenhouse gases occur from this sector. Emissions from this sector include non–energy related emissions from the production and use of cement and lime, chemical industry and metal production as well as F–gases from refrigeration, air conditioning and other industrial and product use. Since 1990, this category has seen a large decline in emissions, mostly due to a reduction in bulk chemical production and metal processing industries and due to changes in process.
The Land Use, Land Use Change and Forestry (LULUCF) sector contains absorbers (sinks) as well as sources of CO2 emissions. LULUCF has been a net sink since 2001. Emissions from this source occur for CO2, N2O and CH4 from clearing of forests and vegetation, flooding of land and from application of fertilizers and lime.
Emissions from the waste sector contributed to <3% to greenhouse gas emission. The majority from CH4 from solid waste disposal on land. Overall emissions from the waste sector have decreased since 1990, mostly due to the implementation of methane recovery systems at UK landfill sites, and reductions in the amount of waste disposed of at landfill sites.
More detailed information and the latest figures are available in the latest National Inventory Report in the Reports section.
In response to the threat of climate change, the Kyoto Protocol was established. Under this agreement, the UK reduction target is −12.5% on 1990 levels (1990 for CO2, CH4 and N2O; 1995 for F-Gases). The UK needs to achieve this reduction during the first commitment period of the Kyoto Protocol which runs from 2008 to 2012.
The Climate Change Act became UK Law on the 26th November 2008. This legislation introduced ambitious and legally binding national targets for the UK to reduce GHG emissions to 34% below base year by 2020 and to 80% below base year by 2050. These targets are underpinned with legally binding five year GHG budgets.
Page last modified: 25 February 2013