<p><strong>Lights from <a href="http://travel.nationalgeographic.com/travel/city-guides/sydney-australia/">Sydney, Australia</a>'s many buildings paint the harbor two days before Earth Hour 2013, which took place on March 23.</strong></p><p>The movement, which began in Sydney in 2007, is a way for people around the world to show their support for tougher action on <a href="http://environment.nationalgeographic.com/environment/global-warming/">global warming</a> by turning off the lights for one hour starting at 8:30 p.m. local time.</p><p>Going dark is just the start for many organizations and governments around the world. Environmental challenges inspired by Earth Hour include planting 500,000 trees in Uganda to highlight <a href="http://environment.nationalgeographic.com/environment/global-warming/deforestation-overview/">deforestation</a> in the African country to gathering over a hundred thousand signatures on a petition to ban logging in parts of Russia, <a href="http://www.earthhour.org/2013outcomes">according to the Earth Hour website</a>.</p><p>The annual event is <a href="http://www.earthhour.org/page/media-centre/faqs">held at the end of March</a> to coincide with the spring and autumnal equinoxes in the Northern and Southern Hemispheres.</p>