Earth Hour is a global event organised by the World Wildlife Fund (WWF). It is a is a "call to action to every individual, every business and every community throughout the world to stand up, to take responsibility and get involved for a sustainable future".

Last year, hundreds of millions of people over 4000 cities in 88 countries took part and switched off their lights for one hour.

How many people will join together this year in "the celebration and contemplation of the one thing we have in common - our planet"?