Could drying the stratosphere help cool the planet?

High-altitude clouds. Credit: Max Dollner, University of Vienna

Yes, but only to a small degree.

While human-caused carbon dioxide emissions are by far the most important driver of climate change, water vapor is actually the most abundant greenhouse gas, and is responsible for about half of Earth's natural greenhouse effect – the one that keeps our planet habitable.

Now, as scientists explore ways to address the impacts of climate change by removing excess heat-trapping carbon dioxide from the atmosphere and by reflecting sunshine back into space, one group of researchers has asked the question: Could removing some water vapor from the atmosphere also help mitigate climate change?
This is precisely the idea explored in a new research article published today in the journal Science Advances that authors have dubbed "intentional stratospheric dehydration" or ISD.

According to lead author Joshua Schwarz, a research physicist at NOAA's Chemical Sciences Laboratory, the ISD concept would involve dispersing small particles (known as ice nuclei) into high altitude regions of the atmosphere that are both very cold and super-saturated in water vapor. These nuclei would increase the formation of ice crystals that otherwise would not have formed.