What percentage of the total greenhouse effect is caused by water vapor?

The answer by Paul B is excellent and there's no need for me to repeat the numbers. Water vapor is certainly the most important greenhouse gas in the atmosphere, but others are important too. If you remove either water vapor OR carbon dioxide from the Earth's atmosphere, the Earth would turn into a frozen snowball in a short amount of time, probably less than a decade. Since these things are somewhat precariously balanced, it's important that we don't cause wide swings in the amount of CO2 either upwards or downwards. The answer by James E is wrong in all sorts of ways. While irrigation can contribute to humidity locally, it is not the primary cause of Palm Springs being more humid than Twentynine Palms. During the months of July, August and September, there is a phenomenon known as the "North American Monsoon" that occurs in the southwestern states. During that time period moist air moves up from the Gulf of California and Eastern Pacific and raises the dewpoints in the desert. A particularly strong manifestation is known as a "Gulf Surge" and it is a strong, low-level tongue of moist air that flows up the Coachella Valley. It can easily be seen from surface observations starting from the southeast and moving northward. When a gulf surge occurs dewpoints in the California deserts can exceed those even in places like Key West, Florida. Since you can see the propagation northward, it is clear that irrigation is NOT the cause of the humidity increase--obviously if the dewpoint in Palm Springs goes from 40 F to 70 F in the course of an hour or two it is NOT because things like lawns and golf courses instantly appeared over that time period. The effects of the gulf surge are less in Twentynine Palms because (1) it is farther north; (2) it is partially blocked from the gulf surge by mountains to the south. Also the higher up you go in the atmosphere, the less water vapor there is on average. He and other deniers try to turn every discussion of science into a political diatribe. It is a laughable that he makes the claim "the real cause of AGW is rich liberals with their extravagant life style of lawns, pools and gardens that pump humidity into the atmosphere warming the local climate"

This is a very good question to which I do not have an answer, but (repeated) here is my idea. • It's actually very simple. Since about the late 1940s people in the west have had access to domestic washing machines, some of the more profligate use tumble driers. Imagine the trillions of tons of fresh water used by these machines and compare it to the amount that would have been used by laundering using two stones or a washboard. Nobody changed their clothes every day as we do now. The wet washing is dried either by hanging out or the tumble drier. Trillion and Trillions of tons of fresh water is thus released into the atmosphere every week, it must fall as rain somewhere. Excess moisture also (as any student of hurricanes knows) changes the way winds blow and air currents circulate around the globe. • The more the wind blows, the warmer it becomes. That's the enemy. There's your problem, Mum doing the weekly wash! QED. Source(s): Been thinking about this for years since I found out that hurricanes start as a zephyr off Africa and pick up energy and hence ferocity as they pass over water