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Researchers trying to save the Great Barrier Reef are attempting to cool the unusually warm sea temperatures using ‘cloud brightening,’ a geoengineering technique designed to reflect more of the sun’s rays away from the Earth. The researchers are 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.

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.

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 project leader and Southern Cross University Senior Lecturer Daniel Harrison.

The research comes after Australia suffered a devastating and lengthy bush fire season that burned nearly 12 million hectares (30 million acres) of bush land, killing 33 people and an estimated 1 billion native animals.

Just before the coronavirus lockdown, the researchers managed to deploy two boats to a site over the Great Barrier Reef, 100 km (62miles) west of Townsville, but without the international researchers who had planned to join them.

They tested a prototype turbine to atomize seawater and blow it into the air, with a drone in the atmosphere and a sampling vessel 5 km (3.11 miles) away on the sea surface. The water droplets evaporate leaving only tiny salt crystals which float up into the atmosphere allowing water vapor 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 nanosized 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 tenfold 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 it’s absolutely essential that we reduce our emissions.”

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