Leading article: Live Earth's great global roar must be heard above the music

Some two billion people are expected to see the various Live Earth concerts around the world today, either by attending the shows or participating via television, radio or the internet. That figure, representing nearly a third of the world's population, cannot be dismissed. Some 150 live acts will kick off in Sydney and finish performing at the Giants Stadium in New Jersey, taking in Tokyo, Shanghai, Johannesburg, London, Rio de Janeiro and New York along the way. The hundreds of events taking place in the cause of Live Earth are about more than music, although that promises to be as superb as it is varied. At Wembley alone, 70,000 fans will hear Madonna, the Red Hot Chili Peppers, Corinne Bailey Rae, Coldplay, Bloc Party and the Black Eyed Peas. It will be the biggest global music event ever.

Yet in a sense it will also have a claim to be the biggest global political event ever. Just as the original Live Aid concert in 1985 helped to relieve starvation and poverty, and Live8 two years ago helped to push the world's largest economies to redouble their efforts to free Africa of debt and barriers to trade, so Live Earth promises to focus attention on the biggest political issue of all: the very survival of the planet. Not everyone, of course, who casually tunes in to see the Foo Fighters will be instantly converted into a green evangelist, but that's not the point or the expectation. Over the past decade or two the environment has moved from being a "fringe" issue, a cause pursued by a few lonely tree huggers, to centre stage, with orthodox politicians from Al Gore to David Cameron and David Miliband championing it.

Indeed it is greatly to the credit of Mr Gore that he has persevered in the face of ridicule when green issues, which he tried to push to the top of the agenda in his time in the Clinton administration, were unfashionable. He has succeeded in organising a vast event; one wonders what the world's future might look like today had he and not George Bush wrangled his way to victory in the flawed presidential election of 2000. As the former vice-president said in his statement launching the Live Earth project: "In order to solve the climate crisis, we have to reach billions of people. The climate crisis will only be stopped by an unprecedented and sustained global movement."

That global movement will find its voice today, with billions involved, people who are gradually becoming engaged in a great crusade, one that is essential if we are to save the planet. That movement has already succeeded in moving the debate to the point where the sceptics - including some of the most obdurate in the Bush White House - now accept the reality of global warming and mankind's role in that as a matter of scientific fact.

So what are the next phases for this global movement? First comes the need to convert the growing consensus on the environment into governmental and individual action. Frankly, it means legislation that hurts, that limits our consumption, that ensures that the costs to the environment are fully accounted for in every sphere of economic activity.

The draft Climate Change Bill published this year should be implemented as soon as possible, with the strict and binding C0 ₂ reduction targets. It means fewer cheap flights; forgoing long-haul holidays; a smaller car; working from home; avoiding the processed and favouring the organic; rejecting excessive packaging. The critics are right about the Live Earth extravaganza itself consuming energy and resources to produce, but if, as a result, governments, corporations and citizens are pushed further and faster down the route of sustainability, then that will have been an extremely worthwhile investment. Enjoy the concerts.