Very interesting study: Continents as sponge landscapes versus deserts. What happens climatically and atmospherically when there is no more water available for evaporation over the continents?
- temperatures rise (due to reduced evaporative cooling)
- precipitation decreases (because evaporation is greatly reduced)
- continental cloud cover decreases (due to lower evaporation)
- this causes the land surface to heat up more
- the residence time of atmospheric water vapor increases by about 50 percent (presumably because there is too little water available for regular cloud formation?)
Abstract:
When we suppress evaporation to create a desert-like planet, we find that temperatures increase and precipitation decreases in the global mean. We find an increase in atmospheric water vapor over both land and ocean in the DesertLand simulation. Suppressing evaporative cooling over the continents reduces continental cloud cover, allowing more energy input to the surface and increasing surface moist static energy over land. The residence time of atmospheric water vapor increases by about 50 percent. Atmospheric feedbacks such as changes in air temperatures and cloud cover contribute larger changes to the terrestrial surface energy budget than the direct effect of suppressed evaporation alone. Without the cloud feedback, the land surface still warms with suppressed land evaporation, but total atmospheric water vapor decreases, and the anomalous atmospheric circulations over the continents are much shallower than in simulations with cloud changes; that is, the cloud feedback changes the sign of the water vapor response. This highlights the importance of accounting for atmospheric feedbacks when exploring land surface change impacts on the climate system.
This extreme experiment raises the question of how real-world changes to the land surface (e.g. land use, agriculture) may be contributing to climate change by altering atmospheric water vapor and cloud cover, and how terrestrial evaporation modulates climate on other planets or in past continental configurations of Earth’s history.
