For decades, the burning of coal to generate electricity has seemed destined for the dustbin of history. What good is a fuel that emits into the atmosphere twice as much carbon dioxide (CO2) — considered the worst of the greenhouse gases — as does natural gas? Britain, for instance, once hoped to reduce its reliance on

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nginx/1.14.0 (Ubuntu) coal-generated power from around 32% to 16% by 2020 as part of its plan to cut carbon emissions by 60% by 2050.

And yet, by all indications, coal seems poised for a comeback. Thanks to high natural-gas prices, worries about gas-reserve levels and the security of supplies, and new "clean-coal" technologies, coal may end up as the bridge fuel of choice to keep Europe's lights burning until renewable, cleaner sources of power become feasible. Richard Budge, ceo of British coal company Powerfuel, says that "a reaffirmation of coal" is under way. Indeed, the British government last week released a report acknowledging that coal will continue providing a third of the country's electricity well into the future. A big factor is demand: global consumption of electricity is expected to double between 2002 and 2030. "World gas resources are not sufficient to meet the world's demand for energy. It can only be done with coal," insists Martin May, spokesman for Swedish power company Vattenfall.

Not that coal ever exactly disappeared. During the cold months of last winter, both Germany and Britain relied heavily on coal to meet power requirements. And coal remains a key power source in many other countries, including Poland, Israel and Spain. But coal use is on the rise, thanks largely to a building spree of coal-fired plants in China and India. World consumption jumped from 3.5 billion tons to 4.6 billion tons between 1994 and 2004.

Part of coal's appeal is relative security of supply. Most natural gas reserves are in the Middle East and Russia; the former is a volatile region, and the latter has shown a willingness to use gas as a political weapon. Coal reserves, however, are globally widespread, and 40% are found in o.e.c.d.countries. Moreover, gas reserves are estimated to disappear within 66 years, but proven, extractable coal reserves could last for up to 200. "World coal reserves are not merely abundant, they are superabundant," Britain's Clean Coal Task Group claimed in a report to the government last month. Britain's homegrown reserves of at least 1 billion tons could last for 60 years, while Germany and Poland have reserves of 6.7 billion tons and 14 billion tons, respectively.

Despite those advantages, coal is still thought of as a dirty, carbon-heavy source of fuel, unwelcome in a world concerned with global warming and the potential environmental crises it could unleash. But that dilemma may be solved by new technologies that could reduce CO2 emissions from coal to nearly zero. Coal-fired power stations using "supercritical" boilers produce hotter steam to run the turbines: 600°C compared to around 540°C in an older plant. Supercritical plants make more efficient use of the energy created by coal's combustion, so less carbon is emitted — around 25% less than the average coal plant. If biomass — an amalgamation of wood, crops, grasses, even household wastes — is mixed with the coal, carbon emissions can be cut by a further 20%. And the resulting electricity is still cheaper than gas-produced power. Supercritical — and now ultra-supercritical — boilers have an additional advantage: they can be retrofitted into older, dirtier plants. Another, slightly less efficient, way to use coal is through integrated gasification combined cycle (igcc) technology, which gasifies coal and uses the resulting hydrogen and carbon monoxide mix to spin the turbines.

On their own, however, these technologies aren't enough to decrease overall emissions because the world's coal-burn rate is rising so quickly. For overall emissions to fall, plants also need carbon capture and storage ( ccs) technologies that shunt the compressed CO2 deep into the ground, perhaps into depleted oil and gas reserves, or into saline aquifers beneath the ocean floor. Sequestration technology works — oil companies have been using it for years — but so far it hasn't been used in conjunction with a power plant. The promise of ccs coal plants has won the approval of some environmental groups. OnEarth magazine, published by the Natural Resources Defense Council in the U.S., recently opined: "Until coal is replaced with cleaner fuels, we must somehow make it part of the solution." Germana Canzi, a senior climate and energy campaigner for Friends of the Earth, says: "We are supporting ccs as an option to bridge the gap between the fossil fuels of today and the cleaner fuels of tomorrow."

There are obstacles that will likely mean we won't see too many full-scale coal-fired plants with ccs technology soon. Building a supercritical, 1,000-MW coal-fired plant with ccs technology from the ground up could cost around $2 billion — about 30% more than the price of a standard plant. Also, pipelines to transmit the CO2 to a burial site need to be built. Legal issues must be tackled, too. For instance, current international treaties that define burial of carbon below seabeds as "dumping" have to be amended. Still, new and refitted power plants using supercritical or igcc technologies could be made carbon-capture ready for little additional expense. "If anyone is building a new coal plant that is not capture ready, they're really stupid," says Jonathan R. Gibbins, an energy expert at London's Imperial College.

There is some movement toward a cleaner-coal future in Europe. Vattenfall is building a $63 million, 30-MW pilot plant in the east German town of Schwarze Pumpe that uses another, untested clean-coal technology: oxyfuel. The plant will burn coal with pure oxygen instead of air, mixed with CO2 to keep heat levels manageable. What's left is pure CO2. Some is recirculated to aid combustion; the rest is easily captured for sequestration. If the combustion technology works, Vattenfall will build a 250-MW demonstration plant that will transport the captured CO2 to an underground storage site. It hopes to start building full-scale carbon-free plants around 2015 to 2020.

In Britain, Powerfuel's Budge expects to break ground early next year on a $1.5 billion, 900-MW plant in South Yorkshire. It's adjacent to the Hatfield Colliery, a shuttered coal mine Powerfuel is now reopening. The plant will use igcc technology, and Powerfuel — now majority-owned by Russia's Kuzbassrazrezugol — expects to pipe the carbon into North Sea–oil reservoirs, where it can help flush out additional oil reserves. Several other carbon-capture ready projects have been proposed. E.ON, for instance, wants to build an igcc plant in the north of England that's capture ready, but says it needs a government subsidy. Imperial College's Gibbins says it's imperative that three to four projects quickly get funded to prove the validity of these technologies. "If climate change is urgent, then carbon capture and storage is a really big deal. And the sooner we do it, the more options we have," he argues. At a time when oil and gas are getting neither cheaper nor more plentiful, the world needs all the options it can find.

• THOMAS K. GROSE
• Cleaner technology and soaring energy demand leaves coal poised for a comeback