Altering clouds to counteract global warming cast in doubt by Irish scientists

The possibility of altering clouds in the world’s atmosphere to counteract global warming has been cast in doubt by research led by Irish scientists.

The study conducted in Antarctica by NUI Galway's Centre for Climate & Air Pollution Studies (C-CAPS) assessed the likely impact of human-led interventions involving methods of "cloud brightening" to counteract climate change.

Marine cloud brightening – an engineering technique also known as cloud seeding or cloud engineering – is a theoretical form of solar radiation management that would make clouds brighter, reflecting a small fraction of incoming sunlight back into space to offset man-made global warming.

Clear evidence that Earth cools after volcanoes erupt, led some researchers to think they should mimic those effects to reduce global warming.

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NUIG researchers from joined the Spanish research vessel BIO Hesperides circling Antarctica’s Southern Ocean, known as “the world’s cleanest laboratory”, to do the study. The purpose of the expedition was also to examine how the world’s atmosphere is functioning in a pollution-free environment.

Clouds, which are made of many droplets of condensed water on air particles, cool the climate by reflecting sunlight. According to recent theories, more air pollution serves as condensation points for cloud droplets leading to more “solar reflectance”.

This has led many to believe that fossil fuel emissions and other air pollutions may off-set global warming through cloud brightening. They advocated manipulation of cloud cover by spraying water-based particles into clouds, thereby reflecting more sunlight back into space, and subsequently reducing radiation.

The Galway study found the addition of a small amount of sea-salt can dampen the effect of clouds becoming brighter as a result of increased sulphate in the atmosphere.

This means recent theories that increased sulphate production can decrease the impact of climate change need to be reconsidered, it concludes. Their findings are published in the latest issue of Nature – Climate and Atmospheric Science.

“Science is clearly pointing to the fact that carbon-based human activity is hurting our environment and there’s only one pathway to solve this – less fossil fuel and no interference with nature,” said C-CAPS director Prof Colin O’Dowd.

“The study backs up our previous thinking that sea-salt will factor out other substances and cause competition between potential nuclei influencing cloud reflectance,” he added.

Lead author Dr Kirsten Fossum said: "Clouds, particularly those overlying dark ocean surfaces, are the Earth's key climate regulators, accounting for half of global reflectance. Pollution-induced changes to cloud reflectance, represent the single biggest uncertainty in predicting future climate change."

The large area covered and systematic evidence from the cruise to Antarctica provided the vast sample of clean air needed to conclusively support this study, he said.

The study was funded by Science Foundation Ireland and the Spanish Ministry of Economy and Competitiveness while the expedition was organised by the Institut de Ciéncies del Mar in Barcelona.