BANGKOK, Thailand - There's no shortage of ideas for high-tech measures to combat global warming: Develop clean biofuels made of corn or palm oil, build more nuclear power stations, or bury harmful carbon emissions in deep vaults.

But those are the last solutions many environmentalists want to hear about.

For the green lobby pushing this week for forceful action at a U.N. conference on limiting the rise in global temperatures, such answers either cost too much, delay an inevitable weaning from fossil fuels, or get in the way of what it sees as the real solutions, such as renewable energy and greater efficiency.

"A lot of technologies that are mentioned . . . are not exactly the most sustainable options," said Catherine Pearse, international climate campaigner for Friends of the Earth. "We may be replacing one existing problem with new ones."

Finding effective mitigation measures at the meeting in Bangkok is crucial to ensuring the world is able to cut greenhouse-gas emissions and keep the atmosphere from warming more than 3.6 degrees.

The Intergovernmental Panel on Climate Change, the U.N. network of 2,000 scientists that has produced two landmark reports on global warming this year, was working on a third study - this one on mitigation measures - for release tomorrow.

Shades of green

A draft of the report features a lengthy list of possible solutions: improved energy efficiency like hybrid vehicles, renewable sources such as solar- and hydropower, cleaner-burning coal and biofuels, reforestation, and even nuclear energy - an option the United States is pushing to give greater emphasis in the final document.

But not all the proposals are equal, environmentalists argue, saying some - such as nuclear - are dangerous, while others, like renewable energy sources, are not given proper emphasis.

The green lobby is a varied group, but the lion's share insist that concern over global warming should not lead to increased reliance on nuclear energy.

Biofuels are seen by many as an excellent option. The U.S. Congress is working on a proposal that would increase production of biofuels, predominantly ethanol, seven times by 2022. Such fuels are made from corn, palm oil, and other agricultural products.

Coal's rise

But where some see a profitable way to wean the planet from gasoline, others see even more environmental damage.

Increasing interest in biofuels is leading to an acceleration of deforestation - a cause of global warming - as lands are cleared to grow palms in places like Indonesia, critics say.

Coal is increasingly taking center stage in the debate: Hard-coal production increased nearly 80 percent from 1980 to 2005, the World Coal Institute says.

Coal, however, is an extremely dirty fuel. Scientists are trying to develop technology to capture the carbon emissions before they are released into the air and to store them underground or beneath the ocean.

Critics argue that the technology is unproven, that storage vaults could leak, and that money spent on developing such measures - prolonging use of fossil fuels - would be better spent on solar and wind power.