Nearly 200 campaigners boarded a special train which is travelling 3,000 miles coast to coast across America this week from California to New York.

The Amtrak train left Emeryvillle, San Francisco, on Monday 15 September 2014 and will arrive in New York in time for the People’s Climate March on Saturday, as a prelude to the United Nations climate summit, which starts on Monday 23 September and involves 180 countries.

"This is an epic journey we are embarking on," Valerie Love, who works for the Center for Biological Diversity, told a cheering crowd outside the station.

Ms Love, 29, added: “It's a big movement. We are telling leaders we need more than talk. We need bold action to leave our children and grandchildren a safe, healthy and liveable future.”

The train was expected to pick up activists in Sacramento, Reno, Salt Lake City, Denver, Lincoln and Chicago.

So many people wanted to take part in the venture that a second train left California on Tuesday 16 September.

Jenna Jablonski of America’s National Association of Railroad Passengers was also on board.

She said NARP wants to be sure that rail, as the most energy-efficient mode of travel, is part of the conversation on climate change. NARP says the data prove that trains are a cleaner way to get around:

Transportation accounts for about 30% of US greenhouse gas emissions (Bureau of Transportation Statistics)

Amtrak is 34% more efficient than cars and 17% more efficient than commercial aviation (Oak Ridge National Laboratory)

Commuter trains are 16% more efficient per passenger-mile than cars and 25% more than light trucks (Oak Ridge National Laboratory)

2.9 billion gallons of fuel were wasted in traffic congestion in 2011 – enough to fill the New Orleans Superdome four times over (Texas Transportation Institute)

Ms Jablonski said: “It makes me feel good to know that when I travel for work, or home to see my family, I can do it in a way that doesn’t dump pollutants into the air, adding to the crisis that is threatening the prosperity of future generations.”

NARP President Jim Mathews said: “Building a future transportation network that grapples with the reality of finite conventional energy sources almost by definition demands rail.

“Even without taking into account the energy and environmental benefits we will get later from innovations like high-speed passenger rail or electric automobiles, passengers are voting with their dollars in favour of lower-carbon travel today.”

The Climate Train is hosting structured seminars and skill-sharing workshops, and there are rallies at several stops along the whistle-stop tour.

Information from Contra Costa Times and NARP