Earth hourThe Empire State Building, the Eiffel Tower, Beijing’s Forbidden City, and hundreds of other world landmarks will be abruptly blacked out tonight. But the 60-minute power outages—scheduled for 8:30 to 9:30 p.m., local time—won’t be the results of a terrorist plot, natural disaster, or massive solar flare. They’re all part of Earth Hour 2011.

The organizers behind the fifth annual Earth Hour urge people to turn off lights and other nonessential appliances in a symbolic show of support for action against climate change and for energy conservation in general.

In 2010, 128 countries and territories took part in Earth Hour. Eighty-nine national capitals participated, as did nine of the world’s ten biggest cities, thousands of other communities, countless businesses, and hundreds of millions of individuals, according to WWF, the international conservation nonprofit, which organizes Earth Hour.

Earth Hour 2011 may be even larger, thanks in part to promotion by world leaders such as United Nations Secretary-General Ban Ki-moon.

“Let us join together to celebrate this shared quest to protect the planet and ensure human well-being,” Ban said in a statement. “Let us use 60 minutes of darkness to help the world see the light.”