By Kirsty Kuo | The Conversation

Marine cloud brightening: it’s a concept that has been floated in climate engineering discussions for some time. But what are the moral implications of this geoengineering technology, and how likely is it to be implemented?

What is cloud brightening?

Cloud brightening is the idea that we could increase a cloud’s albedo (reflectivity) to reflect a greater amount of radiation away from the earth, thus producing a cooling effect. This is one of several ideas for geoengineering (climate engineering); a means of reducing the symptoms of climate change.

Cloud brightening involves seeding clouds with a fine spray of saltwater, which encourages cloud micro-droplets to form. Unlike cloud seeding, where large droplets form and produce a rain shower, the droplets in cloud brightening are smaller and remain in the sky as “white cloud”. The micro-droplets scatter incoming radiation, and increase the longevity of the cloud.

This method would be most effective on clouds over the ocean. Clouds over land already contain small particles of dust and pollution, so the introduction of saltwater aerosol would have little effect.

Cloud brightening falls into the category of geoengineering techniques known as solar radiation management (SRM), together with stratospheric aerosols, space mirrors, and painting roofs white. All of these techniques focus on reducing the amount of radiation reaching the earth’s surface. The other category of geoengineering techniques is carbon dioxide removal (CDR), which involves taking carbon dioxide out of the atmosphere and trapping it in storage.

The cause vs the symptoms

Climate engineering techniques do not address the true cause of the problem of climate change – carbon dioxide emissions. They only have the potential to partially manage some of the symptoms at best. For example, solar radiation management methods do nothing to address the symptom of ocean acidification, and the maximum cooling effect that cloud brightening can achieve is limited.

This is one of the arguments against pursuing geoengineering. Surely we should focus our efforts on mitigation, rather than a partial fix? The answer to this is “absolutely”. Climate engineering is risky and full of uncertainty, and will impact the entire world’s population.

But then what is the motivation for the research that is occurring in the USA and UK into geoengineering methods? This answer is more nuanced, and is based on the timescales that are involved in mitigation and climate change.

Even if we stopped increasing our emissions from today, CO₂ levels in the atmosphere would continue to rise for hundreds of years. Reaching a ‘tipping point’ in the climate may be unavoidable. How likely is it that we will be able to reduce our emissions quickly enough to avoid the worst effects of climate change?

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