The theory behind marine cloud brightening is that brighter or whiter clouds reflect more sunlight back into space. This reduces the heat absorbed by Earth’s atmosphere and provides respite from the effects of increased carbon emissions while we work on lowering them.
It’s thought that clouds over the marine environment have the most to gain from such brightening efforts. But how do you brighten a cloud, and does it work as well in practice as the theory suggests?
The main way that scientists are proposing to brighten clouds is by spraying them with aerosols containing fine particles of sea salt. Aerosols act as ‘condensation nuclei’ in clouds, encouraging water vapour to coalesce and increase the concentration of droplets, leading to thicker, brighter clouds. The same effect occurs with pollution particles.
Working out which are the right-sized particles to deliver to the right types of cloud at the right times is a tricky business, however. They would also have to be seeded on a large enough scale to see the desired results in terms of reflecting sunlight. And what if there are unforeseen effects on clouds or the climate?
Current research efforts involve mostly small-scale experiments and computer simulations, although some real-world studies have proven controversial. In May, city officials put a stop to a cloud brightening experiment in Alameda, California, after being alerted to it via media reports.
Meanwhile, experts have also recently suggested it’s possible to glean useful information from ‘natural’ experiments. Researchers studying clouds near Kilauea volcano in Hawaii showed that the aerosols produced naturally during eruptions increased cloud cover by 50 per cent.
Ultimately, the decision about whether to deploy marine cloud brightening on a large scale lies with policymakers, who haven’t seen enough evidence thus far to convince them of its benefits. But that may change as the science and the climate crisis progress.
This article is an answer to the question (asked by Bethany Shepherd, Derbyshire) 'Could marine cloud brightening help us fight climate change?'
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