The Live Earth concerts taking place across the planet over this 24-hour period will undoubtedly highlight two inconvenient truths about our world. The first will be the ineluctable fact of climate change. The second will be our apparent inability to understand a point unless a celebrity is making it - usually fairly badly.
"We are all fucking conscious of global warming," Bob Geldof claimed charitably this week. "It's just an enormous pop concert or the umpteenth time that, say, Madonna or Coldplay get on stage."
A privilege as it always is to take a lesson from Sir Bob on naive initiatives, this is as ill-informed as it is unfair. Mori research this week revealed that the majority of people on our relatively savvy shores still believe scientists are debating whether human activity contributes to climate change. And so it is that Live Earth overlord Al Gore has judged that you can't make an omelette without breaking a few eggs, which is why private jets, helicopters and limos are being fired up to ferry our well-meaning artistes to various stages.
There is no question that awareness will be raised. But it seems worryingly simplistic to think that there is not a trade-off between raising awareness and using people whom many know to be hypocrites to do so.
There has always been something faintly Marie Antoinettish about rock stars' understanding of green issues. Recently, Jo Wood - self-styled environmentalist wife of Rolling Stone Ronnie - was asked by this newspaper what skills she possessed for a post-oil world. Her answer began: "I come from a family of model makers, artists and sculptors ..."
The Rolling Stones will not be stamping another of their legendary carbon footprints on humanity's face this weekend, but to pluck an example from those acts who will, let's consider Sting, whose band the Police play at the New York concert. Not long ago, this fabled eco-warrior could be found advertising the biggest gas-guzzling Jaguar of them all. To clarify: Sting's personal wealth is estimated at £185m - £185m! You have to ask that if people this rich appear unconvinced that they have enough money to say no to another wedge on principle, then what hope is there that some cash-strapped Chinese worker will start giving serious thought to the kind of fuel choices he's making?
As for Sting's wife, Trudie Styler, it is difficult to know where to start with her recent 80-mile helicopter journey for a weekend at the estate of fellow environmentalist Zac Goldsmith. It beggars belief that these people can continue to be taken seriously by anyone remotely serious; yet there they are, still in the vanguard of celebrity activism alongside London headliner Madonna, whose carbon footprint last year is estimated as the worst of all the artists on the bill.
When considered in this context the kind of bargain required to make the Live Earth concerts happen tends toward the Faustian.
Writing on our engagement with environmental issues in G2 yesterday, George Marshall, the director of the Climate Outreach Information Network, voiced the fear that "we are locked into patterns of collective denial and have adopted a wide range of strategies to avoid accepting personal responsibility". The clear danger with allowing luminously compromised famous folk to front your message is that it allows both them and their audience to reason their way out of changing their behaviour to any significant degree. Your celebrities feel that they have put something back by the very act of donating their services, while your audience can feel justified in thinking - as they trudge toward Wembley tube with Genesis's private jet darkening the skies above them - that they are the least of the planet's worries.
Yet how, when celebrity advocacy has become realpolitik, can Gore's vital message avoid being compromised in this way? For my money, the former next president of the US should play much harder ball with these stars. When Geldof was organising Live Aid, he'd announce the addition of bands to the line-up before even speaking to them. When their managements called yelping that they hadn't committed, Geldof would explain icily that were they not to do so, he would announce that they had pulled out of helping millions of starving children with flies round their mouth (I paraphrase slightly). With the exception of a very few acts, who were publicly pilloried for their selfishness, they opted to remain on the bill.
Given his former line of work, Gore is well versed in the dark arts of campaigning. He should inform as many carefully chosen celebrities as he pleases that he has Swat teams of graduate researchers working round the clock to expose their bad environmental habits, and unless they put paid to them swiftly and publicly, he will use the increasing momentum of his relatively untainted movement to name and shame them.
Harsh, you may say, but it's perfectly fair. It's not as if they'll go hungry. If we are truly to live in a world where celebrities are the medium, then they should pay a little more genuine and practical heed to the message, or forfeit the chance to boost their record sales in front of a global audience of billions.