At 8:30 p.m., this Saturday, people around the world will turn out the lights for 60 minutes to celebrate Earth Hour.
Participants will be switching off non-essential lights and electrical appliances to save energy. In the past the government of Costa Rica has joined in the event by shutting off electricity in San José municipal buildings.
In 2010, hundreds of millions of people in more than 120 countries and territories took part in Earth Hour, according to the World Wide Fund for Nature (WWF).
