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PORTLAND, Maine (AP) - Five busloads of Mainers are taking part in a demonstration in Washington that's being described as the largest climate rally ever in the U.S.

Tens of thousands of people are expected at Sunday's Forward on Climate rally on the National Mall urging President Barack Obama to take action on climate change and reject the Keystone XL oil pipeline that would carry oil derived from tar sands in western Canada to refineries along the Texas Gulf Coast.

It's move forward on climate. Forward on climate. This is not just about tar sands. This is about moving our economy off fossil fuels and moving to renewable sources of energy.

Sierra Club Maine says it chartered four buses and that the Natural Resources Council of Maine chartered another bus to carry more than 300 Mainers to the event. One bus was carrying students from eight colleges and universities.

"I look forward to seeing enough people there so that the exclamation point gets made in the weeks news," says Lee Chisholm from Freeport. "Because I do think climate change is the issue of our time."