As per Wikipedia definition, Earth Hour is:

… an international event that asks households and businesses to turn off their lights and non-essential electrical appliances for one hour on the evening of 29 March at 8 pm local time until 9 pm to promote electricity conservation and thus lower carbon emissions.

Why?
Because climate change is scary as hell. Think about environmental awareness and energy efficiency.

When?
Saturday, March 29th, from 8pm to 9pm.

Just Vancouver?
Are you kidding?! People around the World will be joining together to turn out their lights for Earth Hour, taking a stand against climate change.

How?
There should be a switch somewhere in your house And yes that means also your computer, TV, radio clock, fridge.

WWF Canada one of the promoter, said:

Many iconic buildings and landmarks around the world will be turning out their lights for Earth Hour including the Golden Gate Bridge, San Francisco; Alcatraz Jail, San Francisco; Sydney Opera House, Sydney, Australia; Brighton Pier, UK and the Sears Tower, Chicago.

Canada has one of the highest participation rates around the globe with over 150 cities participating! Many buildings and landmarks will turn off their lights. These include the CN Tower, Niagara Falls, Toronto Eaton Centre, Fairmont Royal York Hotel, Honest Ed’s in Ontario; the Olympic Flag, City Hall Clock and all buildings in which the City of Vancouver operate; and the MacDonald Bridge, City Hall, and Parade Square in Halifax.

Happy, Earth Hour!