As climate change progresses, researchers are exploring climate engineering methods to slow it down or lessen its extent. Some proposed projects involve reflecting incoming solar radiation back into space, keeping it from warming the atmosphere. Along those same lines, a newer approach proposes disrupting the formation of cirrus clouds—the thin, wispy clouds found above 20,000 feet—to let out more longwave radiation that would otherwise remain trapped in the atmosphere.
Earlier climate model studies found that radiation management can suppress the water cycle, reducing rainfall and causing droughts in vulnerable regions throughout the world. Evidence suggests that climate change is already affecting the global water cycle; low-latitude and midlatitude land regions could see increased droughts in the future, whereas global precipitation will increase overall. Understanding how climate engineering techniques might affect the water cycle is important for evaluating their potential usefulness.
Kristjánsson et al. examined the effects of so-called cirrus cloud thinning to find out if the technique could avoid some of the problems that might accompany other radiation management approaches, including suppression of the water cycle.
The researchers used a global climate model to simulate the effects of cirrus cloud thinning. In the real world, scientists would thin out cirrus clouds by using aircraft to seed the cloud formation regions—where the icy wisps form—with small particles to reduce the clouds’ thickness and lifetime. This would allow more longwave radiation to escape from the atmosphere into space.
The team found that unlike other radiation management techniques, cirrus cloud thinning could potentially alleviate the disruption of the water cycle while keeping global temperatures down. This would keep precipitation up in regions that are prone to drought.
Still, cirrus cloud thinning is a very new idea, and it is uncertain whether the technique is even feasible. Meanwhile, the researchers call for more modeling studies to explore its potential effects. (Geophysical Research Letters, doi:10.1002/2015GL066795, 2015)
—Sarah Stanley, Freelance Writer
Citation: Stanley, S. (2016), Could thinning of high clouds combat climate change?, Eos, 97, doi:10.1029/2016EO044307. Published on 1 February 2016.