Steve Connor: Global warming and a coal-fired energy condundrum

Coal made Britain great. It fuelled the Industrial Revolution and powered the first steam engines, but it is one of the dirtiest fuels there is in terms of carbon dioxide and the various noxious oxides of sulphur and nitrogen.

At present, coal-fired power stations such as Drax and Didcot account for about 15 per cent of electricity produced by British power stations. Drax accounts for 7 per cent of the UK's annual electricity needs, enough to power about seven million homes.

It is almost certain that the amount of electricity generated from coal-fired stations will dwindle significantly over the next 20 years, whatever the Government decides over the future of nuclear power.

In 1950, about 90 per cent of Britain's energy needs were met with the help of burning coal. In 2000, gas was the biggest sector, supplying about 40 per cent of our needs, with oil coming second with 32 per cent and nuclear filling the gap by providing 9 per cent of the country's power.

The "dash for gas" in the 1970s and 1980s helped to keep energy prices down, reduce pollution and cut carbon dioxide emissions - but our North Sea reserves of natural gas are running out.

Coal was cheap and plentiful, but costs have risen as mines have gone deeper. Coal-fired power stations are also relatively inefficient at producing electricity. A new coal-fired plant would only have an efficiency of about 40 per cent, meaning that 60 per cent of the chemical energy in a lump of coal is lost during its conversion to electricity. A combined heat-and-power plant can improve this efficiency to between 70 and 80 per cent by using the spare heat given off by burning coal for domestic or industrial heating. The uncontrolled burning of coal produces high levels of sulphur and nitrogen oxides, which cause acid rain. Filters fitted to power station chimneys have reduced sulphur emissions by up to 90 per cent.

Proponents of coal-fired power stations believe that something similar could be done to reduce carbon dioxide emissions. They envisage high-tech filters to remove carbon dioxide, which can then be buried in repositories.

Government advisers have warned that the country needs to have a reliable mix of energy sources and that coal should remain part of that mix for strategic reasons - we still have large coal deposits within our national borders. However, our commitments to reducing carbon emissions will mean that it will be necessary to further improve a coal-fired plant's efficiency and reduce its carbon emissions.

However, China is almost certain to build several hundred coal-fired power plants over the next decade. No doubt coal will help make China great this century.