Al Gore Monday launched a drive to mobilize 10 million volunteers to force politicians to act on climate change - twice as many as the number who marched against the Vietnam war or in support of civil rights during the heyday of U.S. activism in the 1960s.

During the next three years, his Alliance for Climate Protection plans to spend $300 million (about £150 million) on television advertising and online organizing to make global warming among the most urgent issues for elected American leaders.

The wecansolveit.org initiative aims to build up pressure on the next U.S. president to support stringent mandatory emissions controls when they come before Congress, and take a leadership role at the renegotiation of the Kyoto treaty.

Environmental activists Monday described the plan as the most ambitious public campaign launched in the U.S.

"The resources are completely unprecedented in American politics," said Philip Clapp, of the Pew Environment Group. It is equally ambitious in targets. The Alliance has already reached out to organizations as diverse as the Girl Scouts and the steelworkers union to try to broaden its appeal.