So, Earth Hour is this thing where, for one hour, everyone turns out the lights. It's meant to send a signal to take a stand against climate change - though I don't know how much of a difference it's going to make.
In any case, I still think it's a pretty cool idea - it will make some cool photo's from space. Maybe, for that one hour, enough people do it to make a noticeable reduction in emissions for one hour, that it gets extended to "Earth Day", and then "Earth Week", and then "Earth Month". That would be pretty cool.
Here's the link: Earth Hour 2009.