"As humans emit greenhouse gases like CO2, the air warms and holds more water vapor, which then traps more heat and accelerates warming.”
Unfortunately for them, that is just not true and is just not scientifically possible
CO2 doesn’t rise up, trap and retain heat
1.CO2 is heavy and CANNOT remain in the upper atmosphere long, but sinks down. It may be pushed up into the upper atmosphere due to hurricanes or tornadoes, but will sink after the storms subside. eMoody - CO2 Sinks
You see, they want to convince you that CO2 is trapping heat (like a greenhouse) but then don’t tell you how much and for how long. In fact, the only scientist to test CO2 absorption/emission in the open atmosphere is Professor Nasif Nahle (Monterrey, Mexico) in hispeer-reviewed paper, ‘Determining the Total Emissivity of a Mixture of Gases Containing Overlapping Absorption Bands.’ 
Professor Nasif Nahle state: “Applying the physics laws of atmospheric heat transfer, the Carbon Dioxide behaves as a coolant of the Earth’s surface and the Earth’s atmosphere by its effect of diminishing the total absorptivity and total emissivity of the mixture of atmospheric gases.” [emphasis added]
Professor Nahle's study seems to explain why Dr Hansen postulated theory that a rise in CO2 levels would cause global temperatures was so wrong, and that even though CO2 rose at an accelerated rate, temperatures DID NOT RISE as he predicted they should have. link
Does anyone really know what the earths average temperature should be? Every period has a different range. The few thousand years man has been around is just a drop in the bucket of the range of temperatures the earth has undergone. Man had no say in what the temperatures were in the past, nor will he have much to say of where they will go in the future. It is the height of arrogance to think otherwise.