Water Vapor as a Greenhouse Gas
The Distortion
For some reason, climate change deniers sometimes say things that are both demonstrably untrue and are worse for their cause. Case in point: deniers will often untruthfully claim that climate change scientists do not take into account water vapor, a major greenhouse gas.
The Truth
Every major model of climate change takes water vapor into account. Every. Single. One. And, when you look at the reality of it, including water vapor into your model probably makes the problem worse not better.
Here’s why: water vapor does trap heat in the atmosphere, but the amount of water in the atmosphere (and therefore the amount of heat it traps) is a result of how warm the air is, not a cause of it. If there is too much water vapor in the air, it just precipitates out as rain, or sleet, or snow storms. And if the air can hold more, available water evaporates into the air.
But warmer air can hold more water. So as carbon pollution warms our air, the air can hold more water, which causes still more heat to be trapped and the climate to warm even more. Water vapor, in other words, is seen as a multiplier of climate change.
