Question: If water vapour is such a prominent greenhouse gas, should we be concerned with regulation of atmospheric water vapour levels?

Due to the temperature dependence of water vapour concentration in our atmosphere and the rapid cycling of water vapour through the atmosphere, there is little we can do to affect the amount of water vapour in our atmosphere directly.

However, as we change the radiation balance of the earth by adding more greenhouse gases to the atmosphere, the average temperature of the air is likely to increase. This higher average temperature would result in more evaporation and a higher water vapour concentration. In this way, we can affect the water vapour concentration in our atmosphere indirectly as part of a positive feedback loop.

As you learn about some of the other important greenhouse gases, keep in mind how increasing their concentrations in the atmosphere can affect the amount of water vapour in our atmosphere.

Question: Water can be found in all three phases (solid, liquid and gas) under natural conditions. How do you think this property makes water unique among greenhouse gases, enhancing its ability to regulate climate?