The entire Global Warming affair is based on two things, generally accepted by all sides as "fact":

       1. there has been a 1 degree F rise in the average ambient air temperature as measured above land, since the great Irish Potato Famine (circa 1845)

       2. there has been an increase in atmospheric CO₂ during the same period of time, perhaps from 290 PPM to the present 361 PPM

All else is speculation. Anyone who says he knows what the average ambient air temperature will be in 2050 is guessing.