In Sydney, the Opera House has gone dark. In New Delhi, the lights have gone off at the city's great arch. In Kuala Lumpur, darkness has fallen on the Petronas Towers.
Earth Hour lasts for just 60 minutes and its power is purely symbolic. But beginning at 8:30 p.m. local time, in countries around the world, people are switching off the lights in a global call for international unity on the importance of climate change.
Beginning in Sydney in 2007, Earth Hour has spread to more than 180 countries, with tens of millions of people joining in, from turning off the porch lights to dimming the Opera House.