Al Gore, the former American vice-president, yesterday hit back at critics who are labelling him the first "carbon billionaire" from his earnings as an investor in green technology, dismissing them as "global-warming deniers".

Since leaving office in 2001, Mr Gore has become a powerful advocate of government policies to limit carbon dioxide emissions. This week sees the launch of his latest book, Our Choice: A Plan to Solve the Climate Crisis, a sequel to his earlier work, which was also a successful film, entitled An Inconvenient Truth.

As the Copenhagen talks on a new climate-change treaty approach and the US Congress grapples with draft laws to curb emissions, Mr Gore's profile will only swell further. But as it does, so does the chorus asking if his advocacy for action on climate change is about self-enrichment as much as saving the planet.

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Some of his green investments were outlined yesterday by The New York Times. Mr Gore is a partner in the Silicon Valley venture-capital firm Kleiner, Perkins, Caufield and Byers, which has interests in companies developing alternative energy and energy-efficient technologies. He is also a co-founder of London-based Generation Investment Management, which has holdings in eco-energy companies.

He defended his business activities on ABC TV and denied he was on the way to becoming a carbon billionaire. "I am proud to have put my money where my mouth is for the past 30 years," he said. "And though that is not the majority of my business activities, I absolutely believe in investing in accordance with my beliefs and my values."

The new book reiterates the mantra that nothing will happen on climate change without political will. " We need to protect our national security, create more jobs, solve the climate crisis and do right by our kids," he said on ABC.

The book also explores numerous possible solutions to climate change, touching on such issues as forest management, geo-thermal energy and nuclear power generation, drawn from a series of "solutions summits" he held at his Tennessee home with experts.

It was almost inevitable that Mr Gore would become a target of those unconvinced by the alarm bells about global warming, particularly on the American right. "If you really want to save the planet, put down the cheeseburgers and pick up your veggie burger," Glenn Beck, the conservative TV anchor, quipped recently, apparently referring to the dangers of methane emissions from the bovine species.

While the former presidential candidate is not a lobbyist in the traditional sense, he is a frequent visitor to Capitol Hill where he continues to press members of Congress to pass legislation to curb emissions. In April, he was famously put on the spot about his business interests in the industry by the Republican Marsha Blackburn.

Mr Gore, who earns in excess of $100,000 (£60,000) for speaking engagements reacted testily to the implication in her question about a possible conflict of interest. "Congresswoman, if you believe that the reason I have been working on this issue for 30 years is because of greed," he said, "you don't know me".