Is carbon dioxide the most important greenhouse gas?why not water vapor and methane?
It really depends on how you define “important”. Methane is a much stronger greenhouse gas than CO2 (by about 23 times), but there’s not very much of it in the atmosphere, and we don’t emit nearly as much methane as CO2. There’s a lot more water vapor in the atmosphere than CO2, but water vapor by itself cannot cause global warming. The amount of water vapor in the atmosphere depends on the temperature of the atmosphere. If the atmosphere isn’t warming, you can emit as much water vapor as you want and it will just fall back to the ground as precipitation. However, if something else is causing the atmosphere to warm, then it can hold more water vapor, and that increase in water vapor will cause further warming. For this reason water vapor is called a ‘feedback’. CO2 can accumulate in the atmosphere and so can cause global warming. And the amount in the atmosphere has increased by 40% due to humans burning fossil fuels and cutting down forests, etc. So personally I would call CO2 the mos
