US CapitolHundreds of demonstrators are urging Congress to pass legislation to reduce greenhouse gases, and they're using the Capitol power plant as a symbol of the problem. Despite attempts by lawmakers to clean up the power plant in southeast Washington, it still burns coal and accounts for a third of the legislative branch's greenhouse gas emissions. Monday's rally on Capitol Hill was being followed by a march to the power plant, where some demonstrators planned to block entrances and get arrested.

The protest on energy and climate comes as Washington digs out from its largest snowfall of the season. Organizers note that climate change causes more extreme weather, and they say the issue is important enough that people are willing to brave the cold.

They are calling it one of the biggest U.S. protests on climate change — hundreds of activists gathered around a tiny power plant in Southeast Washington that heats and cools the Capitol. While small in size, the 99-year-old facility is a symbol of the challenges ahead for Congress on energy and the climate. That's because as lawmakers gear up to pass legislation to reduce the gases blamed for global warming and clean up the nation's energy sources, they have yet to succeed in their own backyard.

"We are holding it up as a symbol for how we can and must do better," said Mike Tidwell, director of the Chesapeake Climate Action Network, one of 40 environmental groups organizing the protest to call on Congress to pass a bill to curb greenhouse gases. Among those expected to attend are NASA scientist James Hansen, who first testified before Congress about the perils of global warming in 1988.

Hansen has called for a halt on building any new coal-fired power plants without technology to capture and store carbon dioxide, the most prevalent greenhouse gas and the chief one at the Capitol Power Plant. In 2007, the facility released 118,851 tons of carbon dioxide, according to the Energy Department — a fraction of what the nation's 600 coal-fired power plants produce. But despite repeated attempts by Congress to clean it up — including provisions in two 2007 laws — the plant still burns coal and accounts for a third of the legislative branch's greenhouse gas emissions.

Efforts to make the plant run more efficiently, reduce energy consumption and use more cleaner-burning natural gas have succeeded in recent years. But Congress is running out of options to make it fully green. On Friday the House announced that it was abandoning its goal to be carbon neutral and would no longer buy offsets to make sure it was removing as much carbon dioxide from the atmosphere as it releases. Those offsets were key to zeroing out emissions at the plant that could not be reduced by other means.

There are also questions as to whether Congress can afford to pay for more natural gas. The story of the Capitol Power Plant is one likely to play out across the country as Congress looks to limit greenhouse gases and require more energy to come from wind, solar and other renewable sources. The problems that have hampered its cleanup — politics, cost and technological barriers — could trip up similar efforts around the country. Coal-fired power plants are the biggest sources of heat-trapping gases.

It also raises the question: If Congress can't act locally, as the slogan goes, how can it begin to think globally? "They need to start by getting the coal out of Congress," Hansen said. While the use of carbon sequestration technology could reduce carbon dioxide at the facility by about 60 percent, the Energy Department determined in an April 2008 study that the facility was not a good candidate. It cited the $112 million cost, the lack of a place to dispose of the gas, and the increased emissions of other air pollutants that would result from the plant having to burn more coal to run the the carbon-trapping equipment.

Offsetting the power plant's emissions by investing in projects that reduce carbon elsewhere also doesn't look like a viable option. The House spent $89,000 in 2007 and 2008 in part to cancel out the remaining portion of its carbon dioxide emissions at the plant. But on Friday the House said it would no longer purchase offsets because there is no way to verify whether the investment actually results in carbon neutrality.

Recognizing these dead ends, last week House Speaker Nancy Pelosi and Senate Majority Leader Harry Reid wrote to the Architect of the Capitol, which oversees the maintenance and operation of the Capitol Complex, with another recycled idea: convert the plant entirely to natural gas. While four times more expensive than coal, natural gas produces about half as much carbon dioxide.

An earlier effort to rid the plant of coal and oil in 2000 was blocked by two senators from coal-producing states. Democratic Sen. Robert Byrd of West Virginia and Republican Sen. Mitch McConnell of Kentucky argued that continued use of coal would save taxpayers money because it is cheaper than natural gas.

Last week Byrd seemed more willing to compromise, saying he would support having the plant's operators look at ways to increase natural gas use. Switching from coal to natural gas would cost $139 per ton of carbon dioxide saved, or about $2 million a year — and that's just for the House's portion of heating and air conditioning. Converting the plant entirely to natural gas would require $6 million to $7 million in equipment upgrades, in addition to buying more natural gas.

Pelosi and Reid say the investment outweighs the costs. But in the midst of an economic crisis, it is not clear if that would be money well spent.