Can we really count our emissions?

Most of the world's nations struck a major deal on Sunday in Glasgow to do more to bring down their emissions. But for the deal to be worth the paper it's written on, one key assumption has to be true: that we actually know what our emissions are. So can we really keep track of our climate-altering emissions? And if we can't, how much trouble are we in? Featured:  Dr Philippe Ciais, Researcher and Associate Director, Climate and Environmental Science Laboratory, Pierre Simon Laplace Institute, Paris