AGW theory says that CO2 can cause some warming, for example 1C for a doubling of CO2; but that the resulting water vapour feedback will cause an extra 2C or so of warming, which is where the real AGW danger comes from. (Scared yet?)
Climate models [1, 2, 3] and observations show that each 1C of warming causes about a 7% increase in water vapour, which in turn causes a further 2C of warming.
Well, water vapour did just increase by about 7% over course of the year of 2015, but little happened to earth's average temperature; maybe a 0.2C warming at most over the same period:
