I have a Fermi problem for you. By the very nature of a Fermi problem, a precise answer is impossible, we’re merely looking for a justified order-of-magnitude estimate. Here goes:
During last week’s Earth Hour event, what amount of CO2 was not released that otherwise would have been? What is that number in terms of percentage reduction compared to the total worldwide CO2 release during an equivalent time period not during Earth Hour?
Now I’m not knocking the idea. I like to see people avoid trashing the biosphere too badly. Doubly so when it’s possible to shave some money off of the electric bill. I have almost precisely the same set of environmental opinions as Mike Rowe. The Earth is incredibly, unbelievably amazing. So are the staggering wonders of human technological achievement and mastery over many of the forces of nature. They can conflict, but there’s no reason they have to. Those guys Mike meets who turn landfill methane into energy (or any of a hundred other things) do more than any celebrity benefit concert can even think about doing to actually keep the environment on an even keel.
But I’m lapsing into preacher mode here and that’s boring. The Fermi problem was not rhetorical, I’d actually be very interested in a figure. Wikipedia has some local data as a starting point for estimates.
Extra credit: how many coal power plants would have to be replaced by nuclear plants to achieve earth-hour level reductions in emissions rates permanently?