Explainers ·

What is cloud brightening?

Cloud brightening is a world-leading technique to cool and shade coral reefs by boosting cloud cover to reflect light and heat from the sun.

What is cloud brightening?

Sea salt crystals, stirred up by winds from the ocean’s surface, naturally attract and gather moisture, and when air rises they form the beginnings of individual cloud droplets, called nuclei. Low-lying clouds over the ocean reflect sunlight – or solar radiation – and provide shade over the waters and corals below. Fluctuations in sea salt particles in the atmosphere can affect the number of droplets in clouds and so reduce or increase their reflectivity.

Early atmospheric measurements over the Reef have shown the natural concentrations of cloud droplet nuclei may be lower during the summer months when the risk of bleaching is highest than at other times of the year. Cloud brightening works by boosting natural processes during this time, increasing the amount of sea salt crystals in the air and creating brighter marine clouds.

How do you brighten clouds?

A specially-designed seawater sprayer, which works a bit like a snow-making machine, uses surrounding seawater to generate hundreds of trillions of microscopic sea salt crystals. These crystals float into the sky to form a fog and bolster the existing clouds' reflectivity.

The sprayer is attached to a barge so it can be used at specific sites and areas of the Reef, depending on atmospheric conditions.

Does cloud brightening work? 

Our research team, led by Southern Cross University’s Dr Daniel Harrison, began trialling the technology needed to conduct cloud brightening on the Great Barrier Reef in 2020 and the early results are promising. We proved the engineering techniques tested – spraying up a ‘plume’ of sea salt aerosols – can reach the clouds.

Modelling work has shown us that to be effective, sprayers need to operate over weeks to months, lowering the temperature a little each day, when bleaching risk is high. It is not a drastic change, but rather a cooling accumulation in the waters of the Reef over a number of weeks.

If scaled up, we could protect the entire Great Barrier Reef from coral bleaching in a relatively cost-effective way, buying precious time for our Reef while the broader issue of climate change is addressed.  

Why is cooling and shading our Reef important? 

While the world works towards reducing greenhouse gas emissions, there is also an urgent need to explore and develop techniques and strategies now to protect our Reef for future generations, minimising further loss, helping damaged reefs recover and rebuilding vibrant coral ecosystems.

For each year we delay deploying new interventions, the cost to achieve the same outcome increases. Along that timeline we will progressively lose biodiversity that cannot be recovered. By acting now to develop new, safe solutions quickly, we can stay ahead of the curve.

To help our Reef recover, we’re delivering more than 100 Reef-saving projects and the world’s largest coral reefs program. We’re developing, testing and deploying new techniques to protect and restore coral reefs at scale and help them resist and adapt to a changing climate. Cloud brightening is just one part of our innovative cooling and shading work, which can be scaled up and deployed to save corals on the Great Barrier Reef.

Find out about the latest trial here.

The Reef Restoration and Adaptation Program is funded by the partnership between the Great Barrier Reef Foundation and the Australian Government’s Reef Trust. It is delivered by a collaboration between the Australian Institute of Marine Science, the Great Barrier Reef Foundation, CSIRO, The University of Queensland, QUT, Southern Cross University and James Cook University.