Has pop music – an art form that’s supposed to be fun, frivolous and slightly irreverent – ever been as po-faced as it was on Saturday? The Live Earth concert series aimed to “bring together more than 100 music artists and two billion people to trigger a global movement to solve the climate crisis”. Eek! And to think we thought music was here to entertain us! It’s too soon to say whether the sight of six ab-flashing, hip-shaking, tit-jiggling burlesque dancers will impel us stop taking too many plastic bags at Tesco’s, but one vital issue can be tackled now: was Live Earth a good gig?

The London event – one of eight happening across the globe, in seven different continents - started with Genesis. Their four-song set, including spirited versions of ‘Invisible Touch’ and ‘Land of Confusion', made sound etymological sense, but the overall effect was cripplingly middle-aged. Did anyone really think that noodley old dad-rock would be enough to save the planet? It took a youthful jolt of energy from Johnny Borrell and Razorlight to bring the event to life: the London band's renditions of 'In The Morning', 'America' and 'Los Angeles Waltz' were as bright and efficient an energy-saving light bulb.

Sadly, Snow Patrol didn’t seem to realise that playing a song called ‘Shut Your Eyes’ after one called ‘Open Your Eyes’ might be a bit confusing for the audience. Well, which one is it, guys? Should we keep ‘em peeled or are we allowed to take a little snooze before Damien Rice comes on? Of course there was nothing confusing about the day’s message, which was hammered home via a series of cringe-inducing onstage appearances from minor celebrities. T4 presenter June Sarpong, apparently, is the woman best-placed to deliver the kick up the arse that the world needs.

Then - after a barnstorming set from Kasabian, an energetic performance from the Black Eyed Peas and a snoozesome bit of ivory-tinkling from John Legend – Geri Halliwell toddled onstage. Sadly, Ginger Spice wasn’t joined by her four girlie mates, a turn of events that cruelly robbed the gig's middle-stretch of anything resembling the wow factor. Instead, she introduced Duran Duran, who looked rather pleased with themselves for being blessed with the foresight, back in 1980, to write a song called ‘Planet Earth’. Sensibly, they stuck to the hits – ‘Ordinary World’, ‘Notorious’, ‘Girls on Film’ and, of course, that peculiarly prescient slice of new wave – but the effect was somewhat dimmed by the fact we’d seen them do a similar set at the Diana concert six days previously. Still, Nick Rhodes’ hair looked nice.

The Red Hot Chili Peppers offered the day’s first proper singalong moment when they gave us a rampaging version of ‘By The Way’, but Bloc Party’s angular art-rock was too jerky, too knowing and too slight for a gig of this magnitude. Similarly underwhelming was Corinne Bailey Rae, whose pleasant jazz-soul warblings were more suited to the lunchtime stint at All Bar One than an iconoclastic rock concert purporting to save the world.

By now, the end was in sight. The Pussycat Dolls brought a bit of glamour to proceedings, but their set posed as many questions as it answered. Do any of the seven dolls – aside from the ravishing Nicole Scherzinger – actually sing? Which one of them has got the the fittest body? Don't cha feel glad that your girlfriend isn’t the Doll who looks a bit like a man?

And then came the moment that exposed Live Earth’s inconvenient truth: the line-up just wasn’t good enough. Who had Al Gore flown in – not by private jet of course, that would be bad for a rock star’s carbon footprint – to see us through before Madonna came on? Who had the star quality, the multi-generational appeal and the all-consuming enormohits to take such an important spot on the bill? The Stones? Elton? Robbie? Nah, we were fobbed off with the Foo Fighters. Dave Grohl hollered ‘til he was blue in the face for almost half an hour, but it wasn't enough. On these occasions, whether you like ‘Don’t Let The Sun Go Down On Me’ or ‘Angels’ is almost irrelevant; the important thing is that you know, and can chant along to, all the words. Almost nobody at Wembley seemed to know more than a few snatched lyrics of ‘All My Life’ or ‘Best Of You', which is why the Foo Fighters should have come on at 1.45, not 9.45.

But then, before we'd even had time to sulk, Live Earth handed us a nice paradox. Just as Wembley was plunged into darkness to symbolise the energy-saving efforts we should all be making, God gave us light. Strutting like a catwalk model, dancing like a woman who’d lived but half of her 48 years, singing as well as she ever has, Madonna almost managed to save Live Earth. The sight of the world’s most famous woman jigging around the stage with two gypsy punks from Gogol Bordello – although, let’s face it, they could have been any old pair of ragamuffins from the Woolworths doorway – was the first genuinely surprising moment of the day. Followed by a lusty version of ‘Hung Up’, which succeeded in recreating the hedonistic glamour of Studio 54 in a 90,000-seater football stadium, the effect was dazzling. Whether Live Earth was spectacular enough to compel us to combat climate change remains to be seen, but the event did at least reaffirm an incontrovertible truth: The Queen is not dead.