In 2007, the first Earth Hour was held in Sydney, when 2.2 million homes and businesses switched off their lights for one hour from 7.30pm on Saturday 31 March.

It showed Sydney was committed to reduce the threats linked to global warming and Sydneysiders proved that by acting together they could be effective.

In 2008, support for Earth Hour had spread to 35 countries and this year, on 28 March 2009, it is anticipated that Earth Hour will involve at least 1 billion people in 80 countries around the world, including 56 capital cities.

At least 17 of the G20 countries are participating in Earth Hour 2009.

But Earth Hour is about more than one night. It's about inspiring people everyday to make changes that will help achieve Earth Hour's ultimate goal of reducing global carbon emissions by 5%.

The person who initiated Earth Hour is the CEO of WWF, Greg Bourne, who sees Earth Hour 2009 as a global referendum, a visual mandate for change. He says Earth Hour can help set the agenda for the coming eight months, to encourage national and global leadership to make a binding agreement at the Copenhagen meeting of world leaders in December 2009.

Earth Hour 2009 will be held at 8.30pm local time around the world on 28 March.