Forbes: The challenge of global climate change is unprecedented in world history. The fact that a molecule of carbon dioxide emitted in the U.S. is just as harmful to Chinese as one emitted in China is to Americans–or, indeed, to anyone on our planet–means that no human being is exempt from our inescapable commons. This new reality begs a completely new set of global responses. One of the most critical responses must come from the U.S. and China. For without the two largest emitters of greenhouse …