The blockade lasted nearly four hours, forming what organizers called the largest display of civil disobedience on the climate crisis in U.S. history. Police were out in force, but no one was arrested.

The 99-year-old coal fired power station is responsible for an estimated one-third of the legislative branch's greenhouse gas emissions. It is no longer even used to generate electricity but instead acts as a glorified boiler providing steam for heating and chilled water for cooling buildings for the legislative buildings of the Capitol Complex.

Environmental and climate celebrities led the protest action, including NASA climatologist Dr. James Hansen, who released a video on You Tube in February urging people to join him March 2 at the demonstration to send a message to Congress and the President that, "We want them to take the actions that are needed to preserve climate for young people and future generations and all life on the planet."

"What has become clear from the science is that we cannot burn all of the fossil fuels without creating a very different planet," Hansen said. "The only practical way to solve the problem is to phase out the biggest source of carbon and that is coal."

Congressional Democrats have already moved to convert the Capitol Power Plant to cleaner-burning natural gas. On Thursday, House Speaker Nancy Pelosi and Senate Leader Harry Reid released a letter asking the Capitol Architect to switch the Capitol Power Plant from coal to 100 percent natural gas by the end of 2009.

"The switch to natural gas will allow the CPP to dramatically reduce carbon and criteria pollutant emissions, eliminating more than 95 percent of sulfur oxides and at least 50 percent of carbon monoxide," wrote Pelosi and Reid in their letter to Acting Architect of the Capitol Stephen Ayers.

"We strongly encourage you to move forward aggressively with us on a comprehensive set of policies for the entire Capitol complex and the entire Legislative Branch to quickly reduce emissions and petroleum consumption through energy efficiency, renewable energy, and clean alternative fuels," they wrote.

"While the costs associated with purchasing additional natural gas will certainly be higher, the investment will far outweigh its cost," wrote Pelosi and Reid. "The conversion will also reduce the cost of storing and transporting coal as well as the costs associated with cleaning up the fly ash and waste."

"Eliminating coal from the fuel mixture should also assist the City of Washington, D.C., in meeting and complying with national air quality standards, and demonstrate that Congress can be a good and conscientious neighbor by mitigating health concerns for residents and workers around Capitol Hill," the leaders wrote.

"We've been fighting to clean up the Capitol for years - it's an important symbol for the whole nation," said Friends of the Earth President Brent Blackwelder on Thursday.

Last week, Blackwelder and representatives of Earthjustice and the Sierra Club sent letters to Reid and Pelosi asking that they stop using coal at the Capitol power plant.

"Dirty coal plants all over the country continue to release heat-trapping gases and pollute the air we breathe, so there remains much work to be done, but today's announcement is a signal of a major change in direction," Blackwelder said.

"People in D.C. have been fighting against the plant for years, it is very dirty and located in a poor neighborhood. They haven't had much success until now," said Adrian Wilson, a San Francisco-based environmental organizer with the Capitol Climate Action coalition. "The fact that three days before the action, Nancy Pelosi and Harry Reid wrote letter for plant to be switched from coal to natural gas shows the power of direct action to make change quickly."

Bruce Nilles, director of the Sierra Club's Beyond Coal Campaign, said, "Stopping the use of coal at the Capitol Power Plant will help local residents breathe easier, but the positive impacts will stretch far beyond the District. Bold measures are needed right now to reduce global warming emissions and we look forward to continuing to work with Congress and the new administration to send a clear signal to cities and states across the country that after eight long years, America is serious about clean energy and green jobs."

The Capitol Power Plant demonstration was part of a larger movement in the nation's capital on the weekend that lasted through this evening - Power Shift 2009. Some 12,000 college and high school students traveled to DC for the second Power Shift conference, a meeting of students confronting climate change, and business-as-usual attitudes in Washington.

Energy Action, a coalition of 50 environmental groups, organized the Power Shift weekend conference and lobby day. For three days, students attended seminars on the histories of coal power, direct action and uranium mining, media and leadership training sessions, grassroots organizing and anti-oppression workshops.