John Abraham, professor of mechanical engineering, was interviewed by MPR News regarding the climate effects of water vapor.

From the interview:
Water vapor is a greenhouse gas. It’s a little-known, but growing climate concern. An increase in water vapor in the atmosphere is driving more extreme weather around the world.
Abraham: “As we warm the planet, it is causing the oceans to put more water into the atmosphere. As it warms, the world is becoming more humid. The second thing to know is that humidity itself is a greenhouse gas.
“If you have enough heat and moisture for a storm, it can grow and become increasingly powerful. What’s happening is that as we’re warming the planet, we’re not only adding more heat to the world, we’re increasing the water vapor in the atmosphere. It’s a double-headed sword for why storms are becoming more severe.”