This year’s celebrations will be on Saturday 19 March from 8.30pm to 9.30pm. To take part, all you need to do is sign up and switch off your lights for that one hour.

From the Earth hour website: 'It’s a symbolic and spectacular lights out display with a big message – we want to protect the future of our planet!'

Since it first began in Sydney Australia in 2007, the number of countries taking part in Earth Hour has grown to an incredible 172 countries and territories – a number that keeps rising every year!

Earth Hour is not about how much energy is saved during the hour. Rather, it’s a chance to put the spotlight on the issues facing the planet, and to inspire millions across the world to live more sustainably
http://earthhour.wwf.org.uk/whats-happening/