Water vapor trends is a big subject and so this article is not a comprehensive review – there are a few hundred papers on this subject. However, as most people outside of climate scientists have exposure to blogs where only a few papers have been highlighted, perhaps it will help to provide some additional perspective.
Think of it as an article that opens up some aspects of the subject.
And I recommend reading a few of the papers in the References section below. Most are linked to a free copy of the paper.
Mostly what we will look at in this article is “total precipitable water vapor” (TPW) also known as “column integrated water vapor (IWV)”.
What is this exactly? If we took a 1 m² area at the surface of the earth and then condensed the water vapor all the way up through the atmosphere, what height would it fill in a 1 m² tub?
The average depth (in this tub) from all around the world would be about 2.5 cm. Near the equator the amount would be 5cm and near the poles it would be 0.5 cm.
Averaged globally, about half of this is between sea level and 850 mbar (around 1.5 km above sea level), and only about 5% is above 500 mbar (around 5-6 km above sea level).
Read the article