rev 12/31/20,2/26/21 Water Vapor vs  CO 2  for Planet Warming Dan Pangburn, P.E. (ret), MSME, ASME life member Abstract During at least the time period when water vapor (WV) and carbon dioxide (CO 2 ) have been accurately measured worldwide, 1988-now, and apparently for centuries, WV increase has been responsible for the human contribution to Global Warming with no significant net contribution from CO 2 or any other greenhouse gases. Introduction A useful insight to the influence of WV on planet warming can be obtained from understanding why cloudless nights cool faster and farther when absolute water vapor content of the atmosphere is lower; especially when there is no dew or frost. This simple observation demonstrates that water vapor is infrared electromagnetic radiation (IR) active which makes it a so-called greenhouse gas (ghg), thermalization takes place (ghg molecules absorbing radiant heat from the surface or other ghg and sharing the absorbed energy with surr