Read here, here and here. The alarmist AGW hypothesis calls for an increase of atmospheric CO2 to increase atmospheric warming; that will then warm the surface causing increased water evaporation; that will then increase the amount of atmospheric water vapor (the largest greenhouse gas); that will then increase atmospheric warming; that will then warm the Earth's surface; and, etc., in a repeat-the-above scenario of a never-ending positive feedback loop finally leading to the mythical, catastrophic climate tipping points.
What's reality, though?
Ouch....the empirical evidence can be so brutal and unkind to the AGW doomsday-religion and fanatical believers.
From two different sources (click on each image for source), the empirical evidence is clear that atmospheric water vapor component is not increasing with an upward trend as predicted by IPCC's climate models and their Climategate scientists. At best, water vapor content has remained constant with the distinct possibility it has trended down over recent years.
Again, the IPCC's summary reports call for catastrophic calamities/disasters due to a hypothesis that relies on a hypothetical positive water vapor feedback mechanism that does not exist as required and predicted.