A global phase-out of coal is now both necessary and possible, says a report from the Worldwatch Institute.

The report, "King Coal's Weakening Grip on Power", says both environmental and economic trends point towards the abandonment of coal.

The author, Seth Dunn, says: "Coal's share of world energy, which peaked at 62% in 1910, is down to 23% - roughly where it was in 1860." The use of coal declined throughout the 1990s, with a drop of 2.1% in 1998.

Coal is the most polluting fossil fuel

The report argues that coal must go for the sake of the environment, and primarily to slow the onset of climate change.

A cleaner future

However, the World Coal Institute says coal is a fuel for the future, because it is abundant, safe and clean.

Ron Knapp, the WCI chief executive, told BBC News Online: "Using current technologies, coal can now be burnt cleanly throughout the world."

The WCI says subsidies should be used only as short-term measures. But it believes coal offers the best hope of early access to better living standards for the two billion people with no access to commercial energy.

Trans-Pacific pollution

Coal is the most carbon-intensive fossil fuel, emitting 29% more carbon per unit of energy than oil, and 80% more than natural gas. It accounts for 43% of annual global carbon emissions, about 2.7 billion tonnes.

There are thought to be a thousand years' worth of coal left in the ground. But burning it all would release three trillion tonnes of carbon, five times more than scientists say is a safe level for averting serious climatic disruption.

Coal also produces sulphur dioxide and small particles of soot which the report says cause half a million premature deaths a year in the world's cities.

The pollution travels far. Dust clouds from Asian coal now reach the US west coast.

The report says acid rain from coal emissions continues to be a problem. By 2040, half the lakes and ponds in the Adirondack mountains of New York state are expected to be unable to support life.

An industry is dying, but its workers still need to live

It says many countries are now cutting their subsidies to coal producers, and says this trend must form part of a comprehensive strategy to phase out coal.

China has more than halved its subsidies since 1984.

Since that year Belgium, France, Spain, the United Kingdom and Japan have abolished or reduced their subsidies, and together halved their coal use.

Dependency hard to break

But the industrial countries still pay $30 bn annually in subsidies, the former eastern bloc $27 bn, and China and India $6 bn between them.

And many countries are still heavily dependent on coal. It accounts for 78% of overall energy use in South Africa and 73% in China. Denmark uses coal for 74% of its electricity, and the US uses 53%.

The report says the plight of former miners and other coal workers must not be ignored.

There are 10 million coal miners world-wide, less than one-third of one per cent of the global workforce.

There were 705,000 US miners in 1924, and 82,000 today. In the UK the decline has been far steeper: down from a high of 1.2 million to just 13,000.