Ashok Sinha said climate change would end up costing the world trillions of pounds.
Stop Climate Chaos will campaign for action on three key demands. It wants the UK Government to meet its target of cutting carbon dioxide emissions by 20 per cent by 2010, demands that climate change be treated as a top international priority, and urges policy-makers to promote the development of low-carbon technologies.
At the launch, 300 people in white boiler suits gathered under the shadow of the London Eye to form a human version of the campaign's logo.
Sinha told the crowd: "The example you have set today will inspire thousands more to join us, and the action of those thousands will inspire millions more to join us."
Stop Climate Chaos has been devised by the Climate Movement, a broad-based coalition of 18 charities from environmental and development groups, trade unions, women's and faith groups.
Its mission is "to build a coalition that will create a public mandate for political action to stop human-induced climate change".
- See News Analysis, page 10.