This Saturday, 8.30pm, join millions of people around the world in a mass blackout. For one hour, individuals, companies and iconic buildings will be flicking the 'off' switch as a worldwide awareness raiser for climate change. Think of it like an inverse flashmob - synchronised inactivity with a very good purpose. The so-called Earth Hour is coordinated by the WWF, who also want you to register your support online to help petition governments. Several high-profile London attractions have already pledged to join in, including Nelson’s Column, the Coca Cola signs in Piccadilly Circus, the National Gallery, National Theatre, Hayward Gallery, V&A museum, GLA buildings, and the London Eye. You might want to take a candle if you're walking along the South Bank. Let's dim the world together. If nothing else, we'll freak out the astronauts in the International Space Station.