Altering clouds and artificially increasing water movement around stressed corals are two radical solutions that scientists are looking at in order to preserve the Great Barrier Reef.

Back-to-back coral bleaching events, caused by abnormally high sea surface temperatures, have devastated the UNESCO world heritage site, turning once-colourful coral bone white and killing vast swathes of the ecosystem at its northern reaches.

Aerial surveys conducted early this year found severe bleaching had hit two thirds of the reef for the second time in 12 months.

With climate modeling suggesting things are only going to get worse, scientists are looking at a number of ways to engineer a solution.

A group of Australian researchers from the Sydney Institute of Marine Science is working on a plan to brighten clouds above the reef in order to cool the sea surface temperature below.

“The idea is to provide additional cloud condensation nuclei in the form of salt from salt water droplets to create clouds over the reef,” says Daniel Harrison, a postdoctoral research associate with the Ocean Technology Group at the University of Sydney.

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Marine cloud brightening is not a new concept and involves the production of cooling aerosols to help compensate for burning fossil fuels. By producing particles of just the right size it helps to seed white clouds that reflect incoming solar radiation.

This could be a useful tool to help prevent coral bleaching, Harrison believes, which frequently occurs when heightened sea temperatures cause corals to expel tiny photosynthetic algae from inside their tissue, turning them white.

Scientists are experimenting with a number of methods to produce cloud-seeding particles and Harrison says he and his team will be reviewing what’s the most effective over the next year.

“Ideally we’d like to use renewable energy to do this and that might involve a network of ground stations or ocean stations scattered throughout the reef,” Harrison said.

One method being considered is effervescent spray atomization, which involves combining a liquid and a pressurized gas before firing the mixture through a nozzle into the air.

While work on the project is in its infancy, Harrison said early modelling is promising.

“Modelling runs are showing it should be plausible if you reduce incoming atmospheric solar radiation to cool the reef,” he said. “The next stage in the research is to determine if it is also plausible to make enough cloud to reduce the incoming solar radiation.”

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Cloud brightening isn’t the only geoengineering solution that has been proposed to curb coral bleaching.

Local tourism operators in association with the Reef and Rainforest Research Centre (RRRC) want to investigate whether pushing cool water over the reef will reduce heat stress.

Research suggests that corals that are near upwellings, cooler currents, or wind mixing experience less severe bleaching and faster recovery times, the RRRC says.

“The proposal would focus on a limited number of sites that are relatively small in physical area. We are not attempting to pump cold water onto the whole Great Barrier Reef as has been reported elsewhere,” said managing director Sheriden Morris.

The plan, which will be powered by renewable energy, has been submitted to the federal government for funding.