Calling it a visual vote for climate action, organizers of an "Earth Hour" initiative expect 2,800 cities, dozens of companies and hundreds of millions of individuals worldwide to turn off or dim their lights for an hour Saturday night.
Commitments have come in from 84 countries, according to the World Wildlife Fund, which organized the event because of its concerns about warming's impact on humans and wildlife.
"With Earth Hour, millions of people from all walks of life will demonstrate their commitment to take action on climate change," WWF CEO Carter Roberts said in a statement. "Turning off the lights is just the beginning. We're asking everyone to also make commitments to reduce their energy use during the rest of the year and to ask their elected representatives to do the right thing because we need climate legislation now."
Most electricity is produced by burning fossil fuels like coal and natural gas, a process that emits carbon dioxide, a key greenhouse gas tied to warming. While renewable energy sources like solar and wind have no direct carbon emissions, they have yet to displace fossil fuels due to costs and efficiencies.
McDonald's will even soften the yellow glow from some Golden Arches as part of the time zone-by-time zone plan to dim nonessential lights between 8:30 p.m. and 9:30 p.m. to highlight global climate change.
Key landmarks expected to go dark or dim include:
* New York City's Broadway theater signs, Rockefeller Center and the Empire State Building
* The Las Vegas strip
* The Opera House in Sydney, Australia
* The Eiffel Tower and Elysee Palace in Paris
* The Acropolis in Athens, Greece
* The National Cathedral in Washington, D.C.
* Niagara Falls
* The Great Pyramids and Sphinx in Egypt
* The London Eye Ferris wheel
* The Petronas Towers in Kuala Lumpur, Malaysia
Big growth since Sydney start in '07
Seven times more municipalities have signed on since last year's Earth Hour, which drew participation from 370 cities. Earth Hour first debuted in 2007 as an event just for Sydney, Australia. WWF estimated two million people switched off their lights that hour, followed by more than 50 million people in 2008.
Interest has spiked ahead of planned negotiations on a new U.N.-backed global warming treaty in Copenhagen, Denmark this December. The last global accord, the Kyoto Protocol, is set to expire in 2012.
U.N. Secretary-General Ban Ki-moon promoted Earth Hour participation in a video posted this month on the event's YouTube channel.
"Earth Hour is a way for the citizens of the world to send a clear message," Ban said. "They want action on climate change."
Other videos have been posted by celebrities such as rocker Pete Wentz and actor Kevin Bacon, and WWF has offered Earth Hour iPhone applications.
New studies increasingly highlight the ongoing effects of climate change, said Richard Moss, a member of the Nobel Peace Prize-winning Intergovernmental Panel on Climate Change and WWF's climate change vice president.
"We have satellites and we have ships out at sea and we have monitoring stations set up on buoys in the ocean," Moss said. "We monitor all kinds of things people wouldn't even think about. The scientific research is showing in all kinds of ways that the climate crisis is worsening."
Critic to add lighting to store
But not everyone agrees and at least one counter-protest is planned for Saturday.
Suburban Philadelphia ice cream shop owner Bob Gerenser believes global warming is based on faulty science and calls Earth Hour "nonsense."
The resident of New Hope, Pa., planned to illuminate his store with extra theatrical lighting.
"I'm going to get everyone I know in my neighborhood to turn on every light they possibly can to waste as much electricity as possible to underline the absurdity of this action ... by being absurd," he said.
Earth Hour 2009 has garnered support from global corporations, nonprofit groups, schools, scientists and celebrities - including Oscar-winning actress Cate Blanchett and the Archbishop Desmond Tutu.
McDonald's Corp. plans to dim its arches at 500 locations around the Midwest. The Marriott, Ritz-Carlton and Fairmont hotel chains and Coca-Cola Co. also plan to participate.
In the U.S., 220 cities, towns and villages have signed on - from New York City to Igiugig, population 53 on Iliamna Lake in southwestern Alaska.
Among the efforts in Chicago, 50,000 light bulbs at tourist hotspot Navy Pier will dim and 24 spotlights that shine on Sears Tower's twin spires will go dark.
"We're the most visible building in the city," said Angela Burnett, a Sears Tower property manager. "Turning off the lights for one hour on a Saturday night shows our commitment to sustainability."
Power use fell 5 percent in Chicago
The Commonwealth Edison utility said electricity demand fell by 5 percent in Chicago and northern Illinois during last year's Earth Hour, reducing about 840,000 pounds of carbon dioxide emissions.
"It goes way beyond turning off the lights," said Roberts of the WWF. "The message we want people to take away is that it is within our power to solve this problem. People can take positive constructive actions."
While the WWF welcomed even more participants this year, it did draw a line in the electricity sand. "WWF officials stressed the importance of safety during Earth Hour, asking that all lighting related to public safety remain on," it said in a statement.
As for fears of a dangerous power surge if millions turn their power back on at the same time, WWF said it had that scenario covered. "We've checked with energy companies and authorities and turning all the lights back on won't cause any issue," it promised. "The load reduction should not be significant enough to disrupt supply post Earth Hour."
The Associated Press contributed to this report.