What We Don’t Know About Climate Change

We know a great deal about climate change, but there remains a great deal outside our grasp, of which the role of water vapor is an excellent example.  As discussed in the article linked above, water vapor is the single most important greenhouse gas, but it has characteristics that the others (CO2, methane, NO2, etc.) do not; in particular, it condenses at the temperatures and pressures that are present in our atmosphere. 

As we recall from our junior high school science classes, warm air can hold more moisture than cold air.  So this, at first blush anyway, is bad news; as the mean temperatures of the Earth’s atmosphere increase due to global warming, the amount of water vapor increases as well, causing more global warming, etc., in a kind of perpetual feedback loop.

But recall that this characteristic of water vapor, i.e., that it condenses as it chills, is responsible for the formation of clouds, and that clouds tend to reflect some of the radiation from the sun back into space, so that it is not trapped close to the Earth’s surface.

Which phenomenon will prove more dominant?  No one knows, which is why science is much more focused on the non-condensing gases, the most important of which is CO2.