Amanda Sutton looks over a wheat field in northern Colorado and sees a potential "carbon offset project" that could help curb greenhouse gas emissions linked to global warming.

"This is a patch of highly-cultivated land that could provide potential carbon offsets," she said, standing by the field which is owned by the city of Fort Collins and the surrounding county.

"What we would do is take this wheat field and restore it to a native grassland which would sequester carbon from the atmosphere which we could potentially sell," said Ms Sutton, an environmental specialist with the city.

Potential projects in the emerging carbon market are sprouting like wheat after a good rain across the US in anticipation of "cap and trade" provisions in a climate Bill that has narrowly passed the US House of Representatives but could see significant revision in the Senate.

They could be part of a strategy to meet the Bill's current target to cut US greenhouse gas emissions by 17 per cent of 2005 levels by 2020. A cap and trade-inspired market in Europe has been in place since 2005 and is the biggest by far.

Carbon trading and projects are already underway in various versions in the US and contribute to a global voluntary market that last year saw turnover more than double to $705 million, according to Ecosystem Marketplace and New Carbon Finance, which track such trends.

Three regional US groups are trading or in the process of creating regulated carbon trading markets.

To trade on such markets, a project must reduce greenhouse gas emissions or, in the case of converting a cultivated field to its natural state or reforesting a patch of land, act as a "carbon sink" to absorb emissions spewed elsewhere.

Once a project is certified and its "carbon offset" is measured in tons, it can sell them as "credits" to polluters unable to meet their emission targets, or even to groups that want to say they have cut their "carbon footprints".

Some experts say carbon sinks are increasingly important because the world is failing to curb greenhouse gases from power plants, planes and cars fast enough, and so needs to buy more time to avoid dangerous climate change.

But some environmentalists feel trading in pollution is ultimately a ruse.

"By using offsets, industry will be able to sidestep emissions reductions. It is a get out of jail free card," says Damon Moglen, the Global Warming Campaign Director for environment group Greenpeace.

Trees store carbon while they grow and release it back into the atmosphere when they rot. So in the vocabulary of carbon markets a healthy forest is a "carbon sink". Tree growth in the US currently sucks up about 12 per cent of the country's greenhouse gas emissions - a huge total. The US climate Bill may provide an economic windfall to land owners including non-profit organisations, cities, farmers and forest owners who can turn farmland or cleared land back into forests. It may also reward "sustainable forestry" practices, though their carbon benefit will be tough to gauge.

"We see emerging carbon markets as a very exciting revenue source for small family forest owners," said Bob Simpson, vice president for the Center for Family Forests.

Many investments currently being made are essentially "bets" on the Bill that ultimately emerges from Congress, according to Mary Grady, a director at the American Carbon Registry. Ms Grady also said carbon traders worried that the legislation currently says that the "administrator", which depending on the project could be the Environmental Protection Agency or the US Department of Agriculture will approve programmes - but it does not name the programmes yet.

"If it was clear people would have lots of confidence in making their investments but people don't know where to place their bets," she said.

Back at the field in Colorado, Ms Sutton says if this project were to become a reality - a big if - it would have to meet the stringent standards of the voluntary market and show it is removing more carbon from the atmosphere than would have happened naturally. For now, the wheat will remain.

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