Cloud engineering could be a "painkiller" for global warming, study led by University of Birmingham finds

A technique that increases the amount of cloud cover could be an effective "painkiller" for global warming, helping to increase climate cooling.

Marine cloud brightening; a ‘painkiller’ for global warming?
Spraying particles into the marine atmosphere can increase cloud cover and have a cooling effect. Photo by Jason Blackeye on Unsplash.

Marine cloud brightening (MCB) – also known as cloud engineering – involves spraying tiny particles or aerosols into the marine atmosphere where they mix with clouds. These aerosols help to increase the cloud cover and consequently, the amount of sunlight clouds can reflect, having an overall cooling effect.

The climate intervention could be a painkiller, rather than a solution, for global warming say scientists accounting for 69-90% of the cooling effect, much more than previously thought. Their study has been published in Nature Geoscience.

Aerosol injection

MCB has garnered much information in recent years; it could help offset the effects of anthropogenic global warming and help buy some time while the global economy decarbonises. Although previous models estimating the cooling effects of MCB focussed on the ability of aerosol injection to produce a brightening effect on the cloud, just how MCB works to create a cooling effect and how clouds respond to aerosols is poorly understood.

Researchers, led by the University of Birmingham, investigated this phenomenon by creating a "natural experiment" using aerosol injection from the effusive eruption of Kilauea volcano in Hawaii to study the interactions between these natural aerosols, clouds and climate.

They utilised machine learning and historic satellite and meteorological data to create a predictor to show how the cloud would behave during periods when the volcano was inactive, which in turn helped them to clearly identify the direct impacts of volcanic aerosols on the clouds.

Marine cloud brightening; a ‘painkiller’ for global warming?
How MCB works to create a cooling effect and how clouds respond to aerosols is poorly understood. Photo by Billy Huynh on Unsplash.

They found cloud cover increased by up to 50% during the periods of volcanic activity, producing a cooling effect of up to -10 W m-2 regionally (global heating and cooling is measured in watts per square metre, with a negative figure indicating cooling).

“Our findings show that marine cloud brightening could be more effective as a climate intervention than climate models have suggested previously,” says lead author, Dr Ying Chen of the University of Birmingham. “Of course, while it could be useful, MCB does not address the underlying causes of global warming from greenhouse gases produced by human activity.

“It should therefore be regarded as a ‘painkiller’, rather than a solution, and we must continue to improve fundamental understanding of aerosol’s impacts on clouds, further research on global impacts and risks of MCB, and search for ways to decarbonise human activities,” Chen concludes.

Growing evidence

This work adds to the growing evidence that “current climate models may underestimate the impact of aerosols on clouds as they don’t seem to have a strong enough response,” says Professor Jim Haywood, from the University of Exeter and the Met Office Hadley Centre. “More aerosols seem to result in a larger cloud fraction, which cools the climate more than the models predict.”

Haywood says marine cloud brightening could be more effective than previously thought: “However, there is still so much that we don’t understand about aerosol-cloud interactions meaning that further investigations are imperative.”

Experiments using the technique are already underway in Australia in an attempt to reduce bleaching on the Great Barrier Reef, while a team from the University of Washington recently conducted its first outdoor aerosol experiment from a decommissioned aircraft carrier in Alameda, California.

News reference

Chen, Y., Haywood, J., Wang, Y. et al. (2024) Substantial cooling effect from aerosol-induced increase in tropical marine cloud cover. Nature Geoscience.