Lights at about 750 major landmarks also will be switched off.
The World Wide Fund for Nature said the initiative traces its origin back to Australia in 2007 when businesses and residents in Sydney turned off their lights for 1 hour to make a statement about energy use and global warming, RIA Novosti reported Friday.
Organized annually by the WWF for the last Saturday in March, "Earth Hour is your chance to vote for Earth by shutting down your lights between 8:30 p.m. and 9:30 p.m. your local time," the WWF said on its Web site.
"This year, Earth Hour asks people to commit to the event, big or small, for the coming year, taking Earth Hour beyond the hour," said Andy Ridley, co-founder and executive director of Earth Hour.
Cities participating in the global initiative will not just switch off their electricity. They'll also plant greenery and install LED street lamps, the WWF said.