Action on climate depends on estimating what CO2 levels will exist in the future decades. Scientists use assumptions about, for example, CO2 levels in the year 2070 in order to perform calculations of warming. Recently, there has been discussion about the plausibility of the highest emission 'pathway.' We consider some of the implications. Head to "MassClimateAction-dot-org-slash-blog" for the hot links to what we talked about!