Removing excess water vapour from the stratosphere could help cool our planet

A research team at the National Oceanic and Atmosphere Administration (NOAA) is exploring the possibility of removing excess water vapour from the Earth’s atmosphere to combat climate change.

While human-caused CO₂ emissions are by far the most important driver of climate change, water vapour is actually the most abundant greenhouse gas. It is responsible for about half of the Earth’s natural greenhouse effect that helps to keep our planet habitable.

Scientists at NOAA’s Chemical Sciences Laboratory are now exploring whether, instead of removing excess heat-trapping CO₂ from the atmosphere, we look to removing excess water vapour. 

They have called their concept intentional stratospheric dehydration (ISD). It involves dispersing small ice particles into high altitude regions of the atmosphere that are both very cold and supersaturated in water vapour. These particles will then form ice crystals as they head towards the stratosphere in a region called the Western Pacific Cold Point (WCP), which is about the size of Australia.

According to Joshua Schwartz, a research physicist at NoAA, some of the water vapour in that air will condense into ice and fall, thereby removing excess water vapour and dehydrating (at least partially) the stratosphere.

In their study, the researchers used a computer model to simulate the conditions of the WCP, driven by observations of temperature and motions of the tropical air near the stratosphere. This showed that the concept of ISD was effective in theory.

However, it’s not a complete panacea in terms of combating climate change. According to Schwarz, the effect is relatively small and ISD alone would not counteract a large fraction of the warming generated by the CO₂ created by human activities.

Nevertheless, he goes on to say that ISD may be valuable as one element within a larger portfolio of climate intervention and mitigation strategies.

The research team’s findings have been published in a paper entitled ‘Considering intentional stratospheric dehydration for climate benefits’ in Science Advances.