Decline of Great Barrier Reef Provokes Calls for Geoengineering Techniques

Researchers are exploring cloud seeding and pushing cool water over heat-stressed corals as methods for protecting the reef. 

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.

“There is absolutely no doubt this is treating the symptom, not the cause.”

As the impact of climate change worsens, human-engineered solutions may be vital to saving the Great Barrier Reef until greenhouse gas emissions are brought under control, experts say. But tampering with nature comes with a number of risks.

“When you try and save the productivity of something in one part of the ocean, it affects another part. The same thing is true of the atmosphere,” saID Associate Professor Peter Strutton, a climate change and ocean geoengineering expert at the University of Tasmania.

For example, Strutton says moving colder, nutrient-rich water onto the Great Barrier Reef from deeper depths may alter primary productivity.

“In the extreme case, if you had really high concentrations of vital plankton that could decrease the amount of light for corals and that would have a negative effect on them as well,” he says.

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Likewise, extra cloud over the reef will reduce sunlight available for primary producers, such as marine phytoplankton.

While both projects have potential, Strutton said, they would need to be preceded by rigorous small-scale experiments and modelling.

Harrison will assess the potential undesirable side effects of cloud brightening as part of the feasibility study. He’s also quick to acknowledge that geoengineering projects should be paired with cuts to emissions.

“There is absolutely no doubt this is treating the symptom, not the cause,” he said. “It can buy the reef time but it is not going to guarantee the future of the reef if we can’t reduce emissions.”

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