By Mike Collett-White

LONDON, July 7 (Reuters) - More than 100 rock stars play nine concerts across the globe on Saturday in the hope of persuading millions of fans to go green and pressure governments to do the same.

Following in the footsteps of the Live Aid and Live 8 mega-gigs, Live Earth aims to reach up to two billion people through radio, television and the Internet, and features acts including Madonna, Red Hot Chili Peppers, Snow Patrol and Snoop Dogg.

"This is a planetary emergency," organiser Al Gore said, summing up the urgency he and others feel about the need to convince polluters to curb emissions and slow global warming.

The former U.S. vice president and environmentalist told Reuters he wanted Live Earth viewers to pressure leaders to sign a new treaty by 2009 that would cut global warming pollution by 90 percent in rich nations and more than half worldwide by 2050.

He added that the concerts, kicking off in Sydney and ending on Rio de Janeiro's Copacabana beach, were the start of a three- to five-year campaign to promote awareness of climate change.

Gore and his galaxy of pop stars are likely to dominate news bulletins and Web traffic on the day, but there is widespread cynicism among fans and campaigners about using rockers renowned for their conspicuous consumption to promote green living.

"Some people feel that as long as they are preaching the right message, it doesn't matter if they espouse it as well," said Michael Musto, entertainment columnist at the Village Voice in New York. "I have a problem with that."

Bob Geldof, the man behind Live Aid and Live 8, joined the Live Earth detractors, saying the world was already aware of the dangers of global warming and the event lacked a "final goal".

ARTISTS HIT BACK

Some stars appearing at the concerts hit back at the criticism.

"It's easy to criticise but what are you doing?" asked Benin singer Angelique Kidjo at a news conference in Johannesburg ahead of the concert there.

"Get your butt out there and do something. If we don't do something today, then when there's another tsunami then that cynical person, his arse is going to be on that wave."

Concert planners are trying to keep the "carbon footprint" of Live Earth to a minimum, using renewable sources to power the gigs and investing in renewable energy to offset greenhouse gases spewed out by stars' jets or travelling fans.

The event starts in Sydney, and moves on to concerts in Tokyo, Johannesburg, Shanghai, London, Hamburg, New York, Washington and Rio de Janeiro.

There will also be footage from Antarctica, where the previously unknown band Nunatak, comprising two engineers, a marine biologist, a meteorologist and a polar guide at a remote British research station, have recorded a short set.

The "gig" in front of 17 fellow researchers allows Gore to keep his promise to hold at least one concert on all seven continents on the date 7/7/7.

Preparations for the event have not been without hitches.

A planned concert in Istanbul was ditched due to lack of interest and security concerns, while organisers had an 11th hour reprieve in Rio de Janeiro, where a judge lifted a ban on the concert on Thursday.

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