The Empire State Building, the Eiffel Tower, Beijing's Forbidden City, and hundreds of other world landmarks will be abruptly blacked out Saturday night.
(See before-and-after Earth Hour pictures from past years.)
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."
(Related: "This Earth Hour, Don't Forget to Look Up.")
Earth Hour 2011 to Be Extended?
Earth Hour itself doesn't have a significant impact on actual energy consumption or greenhouse gas emissions, which contribute to global warming.
After all, even if electricity use stopped completely during Earth Hour, the event covers just 1 of the 8,766 hours in a year. Of course not everyone participates, and even in areas officially observing Earth Hour, plenty of essential lights and power-consuming appliances are left on.
But Earth Hour isn't about immediate energy impact, organizers say. Rather, it's about demonstrating commitment to change and serving as a jumping-off point for everyday actions.
That's why this year's event introduces "Beyond the Hour," an effort to challenge Earth Hour 2011 participants to choose an action that will help the environment and implement it over the coming year.
So far on the site people have pledged to recycle more, upgrade their light bulbs, ride bicycles, and give up meat, among other actions.
Earth Hour 2001 Backlash
At least one group, the Competitive Enterprise Institute (CEI), a D.C.-based nonprofit libertarian think tank, contends that Earth Hour sends the wrong message.
The organization is holding its own event during Earth Hour 2011—Human Achievement Hour 2011—to celebrate human inventions and innovations that "make today the best time to be alive." CEI's suggested Human Achievement Hour activities include taking a hot shower, watching TV, or phoning friends.
"They want people to turn off all of their lights for one hour on a Saturday night in spring as a symbol of a vote for action on climate change," said Michelle Minton, CEI's director of insurance studies.
"We believe that a vote has to have a choice, so Human Achievement Hour is the alternative, where people think good things about technology as a way to reach solutions to the problems of today and tomorrow."
Human Achievement Hour—including a party at CEI's offices that will stream live on CEI.org—isn't meant to oppose individuals who want to save energy, Minton explained.
But CEI takes issue with those who would, according to Minton, use the environmental movement to encourage governments to force people to conserve.
"We believe that freedom is what's necessary for individuals to come up with improved technologies not only in the West—where we can just flip the switch back on whenever we want—but also in the developing world," Minton said.
"In some places it's Earth Hour every hour of every day."