Here is fun online calculator from Wired illustrating the Kaya Identity. Wired writes:Most of the ways we produce energy end up giving off carbon dioxide—which, in large quantities, screws up Earth's climate. But to reduce atmospheric CO2 we have to understand it. That's where Yoichi Kaya comes in. An engineer at Tokyo University, Kaya and a team of carbon experts put together this formula for computing the total CO2 emissions caused by humans—and where it comes from.If you want to see the Kaya Identity in action, pre-order your copy of The Climate Fix right now. (Thanks JJ)Think about the equation for a while and you realize that if we want to reduce emissions to zero, then either population (P), consumption (g), energy used in production (e), or carbon used to produce that energy (f) must go to zero. Of course, we don't want to depopulate Earth or stop eating and commuting. Energy use might be cut dramatically, but it can't be zeroed out. So reducing any of those factors will just buy us some time to come up with a zero-carbon energy source. Get cracking, scientists!