Across the prairies of Wyoming, past buffalo herds and miles from any town lies the world's biggest coal mine. For 24 hours a day, seven days a week, the North Antelope Rochelle Mine is at work. Using hulking trucks, workers strip off hundreds of feet of grass, soil and rock to get to the coal below.

They blast the coal face into chunks that are crushed and taken by train to 60 power plants on the US's busiest railway. Demand is so high for coal, which fuels 50 per cent of US electricity output, that the process never stops.

Dan Cartwright, the mine operations director, says: "Blizzards slow us down occasionally, but that's it."

Day after day, workers spend 12-hour shifts in their trucks, equipped with water tanks, refrigerators and microwaves to minimise interruptions, taking on load after load. Every day, 15,500 tons are loaded on up to 20 trains. There are more than a dozen mines in the area, the Powder River Basin, which supplies 40 per cent of the US's coal.

The industry estimates that the basin has 100-150 more years' worth of production, based on today's technology. Though most mines are much smaller, there are more than 1,000 of them in the US. The government estimates there are several hundred years' worth of coal to be recovered in the US - the Saudi Arabia of coal, with 27 per cent of the world's known coal reserves. It would take a massive effort to replace coal production. Peabody Energy, which owns North Antelope and is the world's largest private sector coal company, says replacing coal would be a gargantuan task. It would require 2,400 times more solar generation,40 times more wind power, 250 new nuclear plants, almost double the US production of natural gas, 500 hydro plants the size of the Hoover Dam or halving electricity consumption. Even then, the US would have to find a way to meet new demand, given growth forecasts.

Victor Der, principal deputy assistant secretary for fossil energy in the Obama administration, says: "It would be very difficult to move away from it. We believe coal will continue to be in the energy mix."

Yet coal-fired electricity is responsible for enormous carbon dioxide emissions. Coal is the most carbon- intensive of all fossil fuels and the most widely used to generate electricity in the US. Generating electricity is the country's largest source of CO 2 emissions - 41 per cent of the total.

The Environmental Protection Agency estimates the average US coal plant - the biggest source of electricity in the US - emits 4.6m metric tons of CO 2 each year. That is almost double that of a natural gas-fired plant. There are 600 coal-fired electricity plants in the US.

Coal produces a little over a quarter of the world's energy and almost 40 per cent of its greenhouse gas emissions, according to Blackout, by Richard Heinberg, senior fellow of the Post Carbon Institute in California. It is the biggest obstacle to the reduction of global warming.

If no action is taken, says the US Energy Information Administration, the country will emit about 7,550m tons of CO 2 a year by 2030, increasing 2005 levels by more than 14 per cent.

Mr Der says coal is so cheap and plentiful that its usage will grow globally. That is why the US believes the world must learn to capture and store carbon if it is to cut emissions significantly. "I'm optimistic that this will become part of the tools we use to address climate change,'' he says.

Barack Obama, president, from the coal-mining state of Illinois, backs continued coal use. He has said if the US can put a man on the moon, it can find a way to capture and store carbon.

The National Energy Technology Laboratory, owned and operated by the Department of Energy, predicts that by 2012 it will have a portfolio of safe, cost-effective, commercial-scale capture, storage and mitigation technologies ready for the market.

Others are not as confident. Joseph Coote, global energy and chemicals practice leader at Arthur D Little, the consultancy, says: "There is a confluence of challenges here and there isn't a lot of money. It just has the look and feel of a solid decade, with funds behind it, to perfect this. Right now there is so much uncertainty.''

Steven Chu, the energy secretary, has said the administration wants technology for coal-fired power stations to capture and store their CO 2 ready for commercial deployment within a decade.

The US, he says, could have 10-12 commercial demonstration projects operational by 2016, ready for wider deployment by 2019.

The Waxman-Markey climate bill, which is being considered in the Senate, calls for taxing power distributors $10bn over 10 years to fund capture and sequestration demonstration projects. But it gives 10-year breaks to those that capture and store most of their emissions. There is no guarantee the technology will become commercially available at an economic price, providing for widespread adoption.

Stephen Doig, vice-president of the energy and resources team at the Rocky Mountain Institute, which carries out energy policy research, says: "We're pinning our hopes on . . . an unproven technology."

Howard Herzog, principal research engineer at the MIT Energy Initiative, is also cautious: "It can be done. But it's a challenge.''

With many doubting the administration will pass emissions legislation in time for the Copenhagen climate change summit in December, the US faces a struggle in its own backyard: a third of its coal fleet is more than 40 years old and lacks top of the line environmental controls.

Mr Der says putting carbon capture technology on existing coal plants would push up operating costs by 80 per cent.

Much of that will have to be passed on to consumers, who would want assurances it is safe to have large amounts of carbon stored locally. Paul Forrester, a partner at Mayer Brown, the law firm, says: "If you push 20 years' worth of CO 2 in the ground and it leaks out, you're back 30 years. We need it to stay there for ever.''