The percentage of the atmosphere that is water vapor can vary but it's usually 4 percent.
4 percent of the atmosphere is water vapor but it can vary between 3 percent to 4 percent.
The water vapor is the main greenhouse gas on earth.
Water vapor which is the main greenhouse gas on earth is a very important and good greenhouse gas that the earth has.
Water vapor is one of the major contributors to the greenhouse effect on earth.
The water vapor also controls the earth's temperature and without it the earth could not regulate it's temperature correctly.
So it's very important that the earth have water vapor to help control the earths temperature as well as help with the greenhouse gases.