MYTH: Water Vapor is the Most Crucial, Ample Greenhouse Gas, So Why Not Control It Instead of Carbon Dioxide?
TRUTH: Yes, water vapor traps more heat than Carbon Dioxide. But because of the relationship between Carbon Dioxide, water vapor and climate, nations must focus on controlling Carbon Dioxide if they want to fight global warming. It's well-known that atmospheric levels of Carbon Dioxide are determined by how much oil, coal and natural gas we burn, how many trees we cut down and plant growth. Atmospheric levels of water vapor cannot be directly controlled by people. Instead, they are dependent on temperatures. So think of it this way, the warmer the atmosphere, the more water vapor it can hold and, as a result, water vapor is part of an amplifying effect. Greenhouse gases like Carbon Dioxide warm the air and adds to the water vapor, which in turn traps more heat and accelerates warming. Scientists know this thanks to satellite measurements that record a rise in water vapor concentrations as the globe warms.
So when it comes down to it, the best way to lower temperature - and reduce water vapor levels - is to reduce Carbon Dioxide emissions.