Measuring energy's contribution to climate change
Emissions of greenhouse gases like carbon dioxide (CO2) strengthen the greenhouse effect, accelerating global climate change. Generating electricity is one of the biggest contributors to greenhouse gas emissions worldwide.
The contribution of an energy source to climate change is measured by calculating carbon emissions over the lifetime of the generating equipment. An energy source's carbon footprint is measured in grams of CO2-equivalent per kilowatt-hour (gCO2e/kWh) of electricity generated.
Every energy source has strengths and weaknesses, such as its inherent carbon footprint. To meet its carbon-reduction commitments, the UK has to phase out the use of carbon-rich fuels to generate electricity, and to replace them with low-carbon equivalents.
Wind, solar, hydro and nuclear power stations all operate with close to zero CO2 emissions. Any emissions they do produce come largely from building the power station and, in the case of nuclear power, manufacturing the fuel. These emissions are amortised across the long life of the power station.
Power stations that use fossil fuels, such as coal and gas, produce significantly higher levels of CO2 emissions. In the future, this problem could potentially be mitigated by fitting carbon capture and storage (CCS) technology to coal- or gas-fired power stations, but this is not yet proven to work on an industrial scale and they would still produce higher emissions than generating from renewable sources.
Furthermore, CCS will make fossil-fired power stations more expensive to build and less efficient to run, and could lead to issues in the future around storing the captured CO2.
In 2009, about 22% of the UK's electricity came from low-carbon energy sources. The Government recommends that by 2020 this figure should increase to around 40%, and the Committee on Climate Change recommends that by 2030 almost all the UK's electricity needs to come from low-carbon sources. Hence the UK Government favours a transition to a diverse mix of low-carbon generating technologies where the strengths of one energy source compensate for another's weaknesses.
The Greenhouse Effect
The Greenhouse Effect is central to the climate change debate. The effect is a process where radiation from the sun is absorbed by Earth and converted to heat, but is then trapped by the atmosphere.
What does it mean for the UK?
Lowering emissions is vital for the UK energy industry, so the climate change implications of each energy source have important impacts for the UK.
The Energy Sources
Wind farms have a carbon footprint of 11gCO2e/kWh. Wind is not zero-carbon due to emissions from construction, maintenance and decommissioning, but has one of the lowest carbon footprints of the scalable generating technologies.
Solar energy has a carbon footprint of 72gCO2e/kWh. Solar does not look so green when the carbon footprint of fabricating the panels is included. But lower-carbon manufacturing techniques can help to bring this down in the future.
Large hydroelectric power stations have a carbon footprint of around 10–30gCO2e/kWh. Hydroelectric dams require significant quantities of carbon-intense concrete but their long life spreads this over years of near-zero carbon electricity generation.
The carbon footprint of a tidal turbine – the average level of greenhouse gas emissions it is responsible for over its lifetime including manufacture and maintenance – is about 18 grams of carbon dioxide-equivalent for each kilowatt-hour of electricity it generates (gCO2e/kWh). Other marine technologies, such as wave power devices, are still in the early stages of development, so it is not possible to estimate their potential carbon footprint yet.
Nuclear power has a carbon footprint of 16gCO2e/kWh. Most of a nuclear power station's emissions occur at construction and decommissioning. Averaging out these emissions over long years of operation at close to zero-carbon levels puts nuclear power among the low-carbon energy sources.
Gas-fired power stations have a carbon footprint of 487gCO2e/kWh. Gas could play a role in UK generation for many more years with help from carbon capture and storage technology, which could cut a gas-fired power station's carbon footprint to 170gCO2e/kWh.
Coal-fired power stations have a carbon footprint of 870gCO2e/kWh. Coal is the biggest emitter among the popular fuels, so to meet Government climate change commitments no new coal-fired power stations will be built without carbon capture and storage technology – which could reduce a coal-fired power station's carbon footprint to 190gCO2e/kWh.
Oil-fired power stations have a carbon footprint of around 650gCO2e/kWh. The three remaining UK oil-fired power stations, currently used only to hit peak demand, are due to be phased out after 2015.