SYDNEY, Australia — Concerts in Sydney and Tokyo on Saturday kicked off 24 hours of music by more than 150 artists in a round-the-globe series of shows designed to raise awareness about climate change.

Former Vice President Al Gore, whose campaign to force global warming onto the international political scene 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 neighbors, businesses and governments to act as well. That's what live earth is all about."

Madonna, Metallica, the Police and Kanye West were among the top-billed acts listed for the biggest concerts, in London and New Jersey. Concerts also were being held in Shanghai, China; Johannesburg, South Africa; Hamburg, Germany; Rio de Janeiro, Brazil and Washington.

The Tokyo concert kicked off with a high-tech, laser- and light-drenched performance by virtual-reality act Genki Rockets. Later, popular Japanese singer Ayaka urged fans to take up the concerts' theme of changing their daily habits as a first step to reducing global greenhouse gas emissions.

Organizers were predicting live broadcasts on cable television and the Internet could reach up to 2 billion people.