Live Earth
Wembley Stadium, London
THREE STARS

Two years on from Live 8, and nearly a generation after Live Aid, it's not easy for a global mega-gig to make its mark. The early signs were that Live Earth was falling some way short. Maybe it was a mistake to try to scale the same heights without using the toxic, but potent, form of rocket fuel that comes out of Bob Geldof's gob.

The first few hours confirmed the suspicion that this was a noble cause and a rather ordinary line-up. A band like Snow Patrol, who were on third, may sell millions of albums, but they have neither the songs nor the star quality to conquer Wembley. The running order featured several other medium-sized 21st-century acts and only one superstar - Madonna, who went from about fifth on the bill at Live 8 to undisputed queen bee and show-closer here.

Some of Madonna's fellow fortysomethings pulled out the stops. Duran Duran, who were tepid last weekend at the Concert for Diana, found some fire with urgent renditions of Planet Earth and Girls On Film, and the Red Hot Chili Peppers gave the crowd a shot of the hard stuff with their edgy funk-rock. But for the first time in the history of the mega-show, there were not enough dinosaurs.

The only veterans were Roger Taylor of Queen, who led the stirring mass drum solo at the start, and Genesis, who were on next. If you were choosing a single band to represent the first half of rock history, you wouldn't pick Genesis. They opened with an instrumental, and their frontman was at the back, on the drums. This wasn't just eccentric: it was perverse.

Things looked up when Phil Collins got up to sing three of their poppier hits, but as firestarters go, Genesis were a damp match. They even broke the first rule of big shows: if you're playing in daylight, don't wear grey or black - you'll disappear into the backdrop.

Razorlight made the same mistake, as Johnny Borrell chose the wrong moment to ditch his trademark white jeans, but they played with much more energy. They have only two songs that are likely to please a huge crowd, In The Morning and America, so they just played them both, with plenty of swagger, and thus got away with breaking the second rule of giant gigs - don't play obscure album tracks.

Among the younger bands, Kasabian and Black Eyed Peas stood out. Kasabian's Tom Meighan did so literally, by putting on a colourful outfit - a Union Jack shirt. His band were loud, blokey and on-message, like Oasis with added public-spiritedness. Black Eyed Peas, the first band of the day who consisted of anything other than white males, simply worked harder than anyone else. The four of them did a lot of jumping, and so did the joint, and they had the day's first sexy woman in Fergie, who stomped around in denim shorts, looking from a distance like a healthier Kate Moss.

Before Snow Patrol, there was one song, on film, from Nanatak, a band formed by five scientists working in Antarctica - people who really do patrol snow. Their singer just stood there and sang, but he had a soulful voice and an interesting song. We could have done with more of him and less of Snow Patrol.

As an event, Live Earth was working well. Wembley was a picture, the sun was out, and the crowd were up for it. The film-clips about global warming were punchy, not preachy, the atmosphere was genial, and there were some neat green touches, from the globe beach balls bouncing around to the free squares of cotton saying 'Open your mind', which were worn as bandanas, neckerchiefs, French Foreign Legion cap-extensions and Roger Federer headbands.

Musically, however, there had been few memorable moments. David Gray and Damien Rice's stab at Que Sera Sera was fun, if way off-message, Metallica brought some authority as well as heavy riffing, and Corinne Bailey Rae lit up the early evening with a sparky set that included an apt cover of Marvin Gaye's prophetic Mercy Mercy Me. But the show remained resolutely unstolen. The half-time verdict, for all the fine intentions, had to be: less than earth-shattering.

Later on, the Beastie Boys brought some bristling energy, plus an unexpected resemblance to Madness, and Foo Fighters delivered some effective stadium rock, but it was left to Madonna to lift the evening out of the realms of anti-climax. And her set, like the whole thing, was very mixed. Her call to environmental arms, Hey You, was half rousing (a children's gospel choir) and half irritating. The author of Papa Don't Preach has long since forgotten her own advice.

When she strapped on an an electric guitar, for the normally excellent Ray Of Light, she was awful. She can't wear a guitar convincingly, let alone play one. Pausing to speak to the audience, she was even worse - bossy, hectoring and humourless, reprising the moment from Live 8 when she decided to play the gym mistress from hell - although there was one arresting phrase, 'an avalanche of awareness', to remind you that underneath the brittle exterior lies a sharply tuned mind.

But when Madonna remembered that she is essentially a dancer, not a musician, she was very good. She tore off her rather prim black skirt and romped through th surefire disco-pop of Hung Up in skin-tight pedal-pushers, with a hint of the girlish skip that first endeared her to us, a hundred hits ago. She bounced coquettishly off a posse of male dancers in an echo of the Material Girl video. She showed her knack for riding a wave by drafting in the charismatic gypsy punks from Gogol Bordello to add zest to La Isla Bonita. In the end, she did give the show a lift.

Many newspaper writers - and readers - have taken the view that it's hypocritical for pop stars to lecture us about climate change. If so, it is also hypocritical for us newspaper people to have an opinion, because our words are still carried to the paying reader by fleets of trucks, thundering up the motorways late at night. The truth is that nearly all of us in the affluent west have consumed more of the earth's resources than we should have. We are now waking up to that fact. It's a process that most of us are doing slowly, a little painfully, and with alarming amounts of self-consciousness. The earth doesn't care whether one person is smug or another is boring. The earth just needs us to consume less, to turn the tide.

The pop stars have consumed more than most, although we fans have been willing collaborators, buying their all-plastic discs and often driving long distances to their shows. So if they are changing too, that's great – and backstage at Live Earth, there was some rapid education being done to point them down the path of cleaner fuel, less electricity and degradable sets. Hypocrisy isn't when you say one thing, having done another: it's when you say one thing and CONTINUE doing another. We don't know yet that that is happening, so let's hold our fire. We're all in this together.