As Bill McKibben puts it in this eloquent post, physics and chemistry don't negotiate. Yeah, they made good "progress" in Cancun, but that doesn't mean that Global Warming gave an avuncular nod and said "Hey, you did such a good job, we'll just slow the process down for a decade or so and give your compromise time to work."
McKibben's contention is that we already live on a different planet ("Eaarth" - the title of his new book). Here's why:
"As of January 2008, our best climatologists gave us a number for how much carbon in the atmosphere is too much. At concentrations above 350 parts per million (ppm), a NASA team insisted, we can’t have a planet “similar to the one on which civilization developed and to which life on earth is adapted.” We’re already past that; we’re at 390 ppm. Which is why 2010 will be the warmest year on record, almost a degree Celsius above the planet’s natural average, according to federal researchers. Which is why the Arctic melted again this summer, and Russia caught fire, and Pakistan drowned."
Read the rest of his post here.