What would happen if you suddenly removed all the greenhouse gases from the atmosphere?— Ed Hawkins (@ed_hawkins) November 19, 2019
This animation by @CColose shows that icy regions would expand to cover large parts of the planet and global temperature would drop by about 30°C. pic.twitter.com/vB0ckLpezZ
Raymond Pierrehumbert has a nice paragraph in his textbook that explains more:
"One sometimes hears it remarked cavalierly that water vapor is the 'most important' greenhouse gas in the Earth's atmosphere. The misleading nature of such statements can be inferred directly from Fig 4.31.... If water vapor were the only greenhouse gas in the Earth's atmosphere, the temperature would be a chilly 268 K [< 0°C], and that's even before taking ice-albedo feedback into account, which would most likely cause the Earth to fall into a frigid Snowball state.... With regard to Earth's habitability, it takes two [water vapor and CO2] to tango."
- Raymond Pierrehumbert, Principles of Planetary Climate, (2011) p. 271