A two photo combination showing the Elizabeth Tower, which houses Big Ben at the Houses of Parliament in London, illuminated, left, and then in darkness as the lights were turned off to mark Earth Hour 2013, Saturday March 23, 2013. Earth Hour was marked worldwide at 8.30 p.m. local time and is a global call to turn off lights for 60 minutes in a bid to highlight the global climate change. (AP Photo/PA, Lewis Whyld) UNITED KINGDOM OUT NO SALES NO ARCHIVE
It's something of a voluntary rolling blackout: Communities around the globe are going dark for an hour on Saturday evening as part of an initiative called "Earth Hour," to raise awareness of climate change.
In more than 7,000 cities and towns across the planet, millions of residents are turning off their lights for an hour from 8:30 to 9:30 p.m. local time to show their environmental concern.
Here are some photos of "Earth Hour" observances.