Former Vice President Al Gore, whose campaign to force global warming onto the international political inspired the concerts, made a live video appearance from Washington to open the first Live Earth show, on the other side of the world in Sydney.

He took the technology a step further a few hours later, appearing on stage in Tokyo as a hologram to deliver his message.

"Global warming is the greatest challenge facing our planet, and the gravest we've ever faced," he said. "But it's one problem we can solve if we come together as one and take action and drive our neighbours, businesses and governments to act as well. That's what live earth is all about."

For the most part, the diverse range of performers wholeheartedly backed the call, and the organizers promised the huge shows were eco-friendly by using recycled goods and buying carbon credits to offset the inevitable high power bills.

Madonna, Metallica, the Police and Kanye West were among the top-billed acts listed for the biggest concerts, in London and New Jersey, with more modest lineups of mostly local and regional acts at the other venues. Concerts also were being held in Shanghai, China; Johannesburg, South Africa; Hamburg, Germany; Rio de Janeiro, Brazil and Washington.

In Sydney, an estimated 50,000 people grooved through a set by former professional surfer-cum singer-guitarist Jack Johnson, banged their heads to afro-haired 1970s retro rockers Wolfmother, and awaited the first home performance in more than 10 years by reformed 1980s hitsters Crowded House.