In: Economics
Andorra and the Vatican City are regarded as the process's' observers' and have not been asked to sign. The combined population of both is likewise 52. Southern Sudan is the newest nation in the world, and has been around for only a matter of months. It is understandable that its leadership did not get around to signing a 1997 climate agreement. It has probably not even filed all of its paperwork on' new nation' yet. As you know, Taiwan is experiencing constant political problems as a result of omnipresent tensions with China; it is not legally its own state and therefore it is a matter of contention whether or not it can ratify Kyoto.
That leaves the U.S. and Afghanistan as the two sole nations which have no excuse not to sign Kyoto. It's not like one of those countries has become an active war zone for the last decade Maybe one of the reasons that Afghanistan has not yet signed Kyoto is because it was too busy fighting tribal insurgencies and being bombed by the other non-signer. So, that leaves the USA. The planet's largest economy, historically the richest nation.