But a top scientific forum here shows how far the argument for carbon sequestration has come, with a series of experts insisting it can be transformed from fiction to fact.

Driving their case is the fear that time is running out for dealing cheaply with the carbon pollution spewed out by fossil fuels.

These emissions trap the Sun's heat and disrupt Earth's fragile climate system, with potentially catastrophic effects a few decades from now.

Their focus is on power stations which burn oil, gas and coal, and whose pollution is set to soar in coming years as China and India, the two world's most populous countries, meet surging needs for energy.

Sequestrators say carbon dioxide (CO2) would be captured using solvents, either before or after the fossil fuel is burned in the plant.

The CO2 would then be pumped out, sometimes over hundreds of kilometers (miles), to disused oil and gas fields up to one kilometer (3,250 feet) underground, and stored.

It would not be the miracle cure to global warming or switch off the dependence on fossil fuels that are the source of the problem, they admit.

Even so, "it can play a global role, making very large and very rapid reductions of CO2 emissions," Jon Gibbins of Imperial College London said on Thursday.

He pointed to a pilot scheme in the North Sea as proof of its feasibility.

An experiment in Norway's offshore field, Sleipner, has been storing a million tonnes of waste CO2 per year since 1996, pumping it 1,000 metres (3,250 feet) below a cap of shale and mudstone.

Another project is in North America, where CO2 is being extracted from a coalgas plant in Wyoming and pumped 300 kms (185 miles) to Weyburn, in Canada's Saskatchewan province, where it is stored in an empty underground chamber in a working oilfield.

Environmentalists say the answer to global warming is to slash emissions themselves and swiftly wean the world off dirty fossils and onto renewable sources and hydrogen.

They also warn that the stored carbon is simply a bequeathed hazard for future generations. If the geological storage tank leaks or is breached by an earthquake the outpouring of CO2 would instantly damage the world's climate system.

Gibbins says former oil and gas fields in sedimentary basins, but also many types of water aquifers, are excellent options for safe storage: "We are looking at 90 percent retention [of the gas] for 1,000 years."

Taking out the CO2 from fuel is called "carbon neutral," in other words not adding further to emissions from that source.

But a more ambitious possibility is "carbon negative," or removing CO2 from the atmosphere.

That could be done by biofuels, suggests Peter Read, a professor at Massey University in New Zealand.

Plants suck CO2 out of the air as part of photosynthesis. By growing plants, burning them in fossil-fuel power stations and then sequestrating and storing the carbon, a dent could be made on atmospheric CO2 levels, he said.

"Don't dig for your energy - grow it," he said. "In the right conditions, you could produce all the world's needs for electricity and liquid fuels from biomass."

Typical plants could be willows, pines and other resinous trees, supplemented by seasonal crops such as corn and sugar, he said.

Former Greenpeace campaigner Bill Hare, now a visiting scientist with an eastern German institute on climate change, said the push for carbon sequestration was hated by many environmentalists as a sop to the oil and coal lobbies.

But some were grudgingly accepting it as a bridging solution between the carbon and hydrogen ages, Hare said.

"Speaking personally, I believe that all power plants being planned now should be fitted with sequestration technology. We're going to need it," he said.

The International Energy Agency (IEA), in a 2004 prediction on world energy needs over the next 25 years, said emissions of CO2 from all sectors would increase by 62 percent.

During the same period, world electricity demand is projected to double, with fossil fuels supplying most of the need.

The three-day conference, ending in this southwestern city on Thursday, focussed on scientists' latest assessment of the global warming problem.

All rights reserved. � 2004 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.

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