Which greenhouse gas is the most responsible for Global Warming- CO2, methane, water vapor?
Wilipedia has a pretty good treatment of this
en.wikipedia.org/wiki/Greenhouse_gas
.
Also be aware that while the water vapor number is greater than the CO2 number, it is largely a stable number while CO2 is increasing, and also that the effect of water vapor is somewhat self-mitigating as discussed below. So, "responsible for global warming" is the largest aggregate increase in effect over time - the clear winner is CO2.
CO2 also matters more because it is pretty inert and thus has a long residence time in the atmosphere (decades). CO2 concentrations will continue to increase even if the year-over-year emission rate of CO2 into the atmosphere decreases. It will require very aggressive reductions in CO2 emissions to stabilize the CO2 level in the atmpsphere.
Wikipedia In part:
The contribution to the greenhouse effect by a gas is affected by both the characteristics of the gas and its abundance. For example, on a molecule-for-molecule basis methane is about eight times stronger greenhouse gas than carbon dioxide[6], but it is present in much smaller concentrations so that its total contribution is smaller. When these gases are ranked by their contribution to the greenhouse effect, the most important are:[7]
water vapor, which contributes 36–72%
carbon dioxide, which contributes 9–26%
methane, which contributes 4–9%
ozone, which contributes 3–7%
....
Water vapor accounts for the largest percentage of the greenhouse effect, between 36% and 66% for water vapor alone, and between 66% and 85% when factoring in clouds.[8] However, the warming due to the greenhouse effect of cloud cover is, at least in part, mitigated by the change in the earth's albedo. According to NASA, "The overall effect of all clouds together is that the Earth's surface is cooler than it would be if the atmosphere had no clouds."
