Citizens' awareness and involvement concerning the most important environmental issues that the world is facing, such as climate change, represent the winning point of Earth Hour. Launched seven years ago by the World Wildlife Fund (WWF), its major aim is to mobilize people to take action against this global key problem.
Individuals, businesses, governments and communities are invited to switch the lights off for one hour. This easy action symbolizes the willingness to adopt a more sustainable lifestyle.
The numbers reached thus far by the event are huge: last year more than 2 billion people, 7000 cities, 152 Countries and 154 companies were involved. In 2013, Earth Hour will happen on March 23 from 8.30 pm to 9.30 pm anywhere in the world.

The impacts of the initiative, however, go beyond the hour. Launched in 2012, the "I Will If You Will" campaign invites individuals and organisations to challenge others to an environmental commitment by promising to do something if a certain number of people accept their challenge.
The "Earth Hour City Challenge", on the other hand, rewards cities that are making the best efforts to be greener, cleaner and more sustainable. This year 17 cities and municipalities from Canada, India, Italy, Norway, Sweden and the United States of America were selected, and people could cast their preference to elect the Global Earth Hour Capital. The city that received the most votes was Vancouver, Canada.

Please find more info on the official website for Earth Hour.