Earth hour is an example of how ignorance breeds odd developments. The idea is this: cities around the world turn off as many lights and appliances as possible for one hour this coming Saturday so as to have an impact on global warming. The underlying assumption is that lowering energy demand will reduce CO2 emissions and this in turn will have some sort of impact on the climate some eight hundred years from now. More significantly, according to the organizers, switching off your lights for one hour will be a "vote to save the planet" - something that can be taken to the world's leaders in Copenhagen in December. A symbolic "lights off for our future!".
Its not a bad thing to reduce energy consumption and it will be fun to have the concert and all that transport used to get people to the celebration (which will probably counter the savings). But the idea that this will have an impact on the planet is, well, simply naive.
Apart from the fact that most CO2 is absorbed quickly and that the life-time of the remaining CO2 is 4-7 years, the evidence that minor and symbolic changes to behaviour have an impact in climate is currently zero.
Further, when others have done this – Britain had a day recently when it asked the population to systematically reduce energy demand – no discernible difference was seen in energy consumption across the nation.
So, don’t expect things to change when you sit in the dark for an hour next Saturday between 8.30pm and 9.30pm.
Also, don't expect the politicians to be influenced some eight or nine months from now either.