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In Sydney, the Opera House went dark. In New Delhi, the lights were switched off at the city's great arch. In Kuala Lumpur, darkness fell on the Petronas Towers.

It lasts for just an hour and its power is purely symbolic. But in countries around the world, at 8:30 p.m. local time, people were switching off the lights Saturday for Earth Hour, a global call for international unity on the importance of climate change.

Since 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 letting the Opera House go dark.

Those 60 minutes are "an opportunity to adopt a shifting of the consumption culture, and behavior change towards sustainability," Indian Environment Minister Harsh Vardhan said in a statement.

Many people, of course, barely notice. Around India Gate, New Delhi's monument to the Indian dead in World War I, thousands of people continued Saturday with the city's nightly warm-weather ritual. They bought ice cream and cheap plastic trinkets. They flirted. Young children rode in electric carts that their parents rented for a few minutes at a stretch.

But for an hour the arch stayed dark, a silent call for change.

In Jordan, the Royal Society for the Conservation of Nature arranged 11,440 candles on a hilltop in the capital of Amman, establishing a Guinness World Record for the largest candle mosaic.

The candles spelled the Earth Hour motto of "60+." However, attempts to light the candles largely failed because of wind on the hilltop, which is close to the city's landmark, the Amman Citadel.