Researchers trying to save the Great Barrier Reef are attempting to cool the unusually warm sea temperatures using cloud brightening (also known as cloud whitening), a geo-engineering technique designed to reflect more of the Sun’s rays away from the Earth.

What is cloud brightening?

Project leader and Southern Cross University lecturer Daniel Harrison said cloud brightening was one of the most innovative and promising potential methods that could protect very large areas of reef.

“Cloud brightening could potentially protect the entire Great Barrier Reef from coral bleaching in a relatively cost-effective way, buying precious time for longer-term climate change mitigation to lower the stress on this irreplaceable ecosystem,” Harrison said.

“Microscopic sea water droplets are sprayed into the air, evaporating leaving just nano-sized sea salt crystals which act as seeds for cloud droplets, brightening existing clouds and deflecting solar energy away from the reef waters when heat stress is at its maximum. In the future this technology might be able to be applied over the Great Barrier Reef to reduce the severity of coral bleaching during marine heat waves, cooling and shading the corals below,” he said. 

What is the significance of such an experiment? 

In the last few weeks, and for the third time in five years, the Great Barrier Reef has suffered a mass bleaching event where stress from unusually warm water temperatures bleach the coral white and can kill it.

Bleaching occurs when healthy corals become stressed by changes in ocean temperatures — causing them to expel algae, which drains them of their vibrant colours.

February was the warmest month on record in terms of water temperatures around the reef, with readings in some places of more than 3 degrees Celsius above average for the time of year. 

“If we can brighten the clouds just a little bit over the whole summer, then we can cool down the water enough to stop some of the coral bleaching,”  said Harrison.

The research comes after Australia suffered a devastating and lengthy bushfire season that burned nearly 12 million hectares of bushland, killing 33 people and an estimated 1 billion native animals.

How is the experiment conducted?

The team is spraying microscopic sea water droplets into the air over the reef, which creates more cloud cover and more shade in an effort to save the health of one of the world’s most important marine ecosystems.

Just before the coronavirus lockdown, the researchers managed to deploy two boats to a site over the Great Barrier Reef, 100km west of Townsville, but without the international researchers who had planned to join them.

They tested a prototype turbine to atomise seawater and blow it into the air, with a drone in the atmosphere and a sampling vessel 5 kilometres away on the sea surface. The water droplets evaporate leaving only tiny salt crystals which float up into the atmosphere allowing water vapour to condense around them, forming clouds. 

“When we did all the analysis cloud brightening came out as really one of the better ideas that we’d found because there’s very high energetic leverage,” Harrison said.

“So just a small amount of energy to produce these nano-sized salt crystals results in a very large amount of energy getting reflected back from the cloud and cooling down the coral,” he added.

Next year, the team plans to test the technology at three times the size, ready for a ten-fold increase a year later, which the researchers say should be able to brighten clouds across a 20-by-20-kilometre area.

If we find out that this technology works as well as we hope then one day we could have these machines scattered all through the Great Barrier Reef, Harrison said. 

This might buy us a couple of decades but at the same time its absolutely essential that we reduce our emissions. 

Great Barrier Reef

The UNESCO World Heritage-listed Great Barrier Reef World Heritage Area is a vast and spectacular ecosystem with one of the world’s most unique collections of biodiversity. 

Stretching 2,300 kilometres along the Queensland coastline from Bundaberg in the south to Cape York in the north, the Great Barrier Reef is approximately 348,000 square kilometres in size. This vast expanse is bigger than the United Kingdom, Holland and Switzerland combined, with over 2,900 coral reefs and 1,050 islands and coral cays. 

It has an incredibly diverse ecosystem, home to 1,500 species of fish, more than 30 species of whales and dolphins, six of the seven species of marine turtles and 22 species of seabirds.

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