During Earth Hour, on March 28, everyone is asked to turn off their power for one hour, starting at 8:30 p.m. local time, in a symbolic stance against global warming.

The World Wildlife Fund started the event two years ago in Sydney, with 2.2 million people and thousands of businesses going dark. The next year, more than 400 cities and 50 million folks on all seven continents participated. Some high-wattage landmarks even got involved, including the Sydney Opera House and, in New York, the Coke billboard in Times Square and the Empire State Building. For 2009, so far nearly 1,200 cities — including Chicago, Guatemala City, Vancouver, Mumbai and Bangkok — in 80 countries have signed on. Group organizers aim for 1 billion people to flick the switch, an achievement they hope to present at the U.N. Climate Change Conference, to be held in Copenhagen this year.

Some cities and tour companies are turning the statement into a celebration. Luxury tour operator Abercrombie & Kent, for one, is organizing stargazing parties at 13 African lodges and sanctuaries, which themselves plan to reduce energy consumption by half. Melbourne, Australia, is hosting a people-pedal-powered concert, and, in Athens, a conductor will lead a percussion circle as the Acropolis dims.

You can do your part on the road, too: Kill the room lights and TV, turn off the appliances, switch from plug to battery at the Internet cafe. Just remember to pack a flashlight, preferably solar-powered. For more information: www.voteearth2009.org.