Concerts for causes can be tricky. There’s no way to be perfectly pure and righteous, especially with concerts devoted to environmental issues. Musicians whose main job is showing people a good time can be awkward attempting to promote virtue. (Sydney’s first band, Blue King Brown, had no problem with that, however: It’s a funk and reggae agitprop group urging people to unite and fight the system.)

Live Earth is designed to be carbon neutral, adding no net difference to greenhouse gases despite its demand for wattage and gasoline. Between sets, the netcast has shown some relentlessly clever promotions for recycling and conservation. “If everybody boiled only the amount of water they needed for tea…” O.K., I just unplugged my cell-phone charger. But I can’t be the only one who marvels that the MSN netcast is sponsored by Chevy.