It looks like Earth Hour — the one hour a year when everyone turns off their lights as a symbol of concern over global warming — is going to be huge this year. Seventy-four cities in 62 countries have already committed, and organizers are hoping to reach a billion people in 1,000 cities by the time the hour itself rolls around on 28 March 2009.

Not bad for something that started with one city in 2007 and struck, er, some as a kind of empty symbolism. Get a billion people involved and, well, your symbolism isn’t so empty any more. Here’s a video to pass around:

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