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Cloud brightening might be the silver lining that saves the Great Barrier Reef from bleaching

Brightening clouds above the Great Barrier Reef could save the coral below, Australian scientists believe.

University of Sydney postdoctoral research associate Daniel Harrison said marine cloud brightening (MCB) technology could give the whole reef a chance at survival.

“We think this technology should work, could potentially save more or less the entire reef from bleaching, involves only a very short-lived atmospheric effect and has minimal risks of adverse side effects,” he said.

“The alternative is almost certainly that we watch the reef disappear before our eyes – within perhaps less than a single generation.”

The process of MCB involves making a cloud more reflective by increasing the number of cloud condensation nuclei (CCN).

“Because of what’s known as the Twomey effect, a larger number of smaller droplets reflect more light back into space. By providing the additional CCN, we can reduce the incoming solar radiation during the warmest periods when coral bleaching is imminent,” Harrison said.

“Ocean temperatures in the bleached region of the reef during 2016 were about 0.8 degrees Celsius above the normal summer maximum. If we can cool the water by this much, bleaching should be mostly avoided.”

Cooling water to that extent would require brightening clouds over several weeks or months during the warmest period of the year. But with current levels of global warming, Harrison said that cloud brightening would only be needed in hot years.

He has recently been awarded an innovation fellowship from the Myer Foundation, which will allow him to concentrate full time on investigating the technology for MCB.

“I will work on design and prototyping of a system that can meet the targeted cloud brightening using natural seawater droplets to create the additional CCN,” he said.

Harrison is hoping to develop a system capable of running entirely on renewable energy.

“The Great Barrier Reef extends over an area around 345,000 km2, and MCB offers the ability to achieve very high energy leverage, without which altering the temperature of such a staggeringly large amount of water would be prohibitively difficult,” he said.

“A single nozzle can produce trillions of salt water CCN per second from just milliliters of seawater, while natural atmospheric updrafts and the wind can help distribute them over the very large areas required.

“The physical effect is multiplied by the natural process of moisture in the air condensing onto these nanosize particles, thus increasing their volume by several orders of magnitude, which then reflect some of the sun’s radiative energy.

“The energy we need to put in to create the condensation nuclei is an extremely small fraction of the energy we are able to block from the sun. Best of all, the process replicates natural processes and uses only sea water, no chemicals.”

Harrison is part of a team of researchers at the Sydney Institute of Marine Science working on technologies for mitigating coral bleaching.

They have looked into everything from wave driven pumps to move water from the deeper ocean to cool the reef, using heat exchangers between the deep ocean and near surface reefs, genetic engineering of temperature-resistant corals, transplanting corals from warmer oceans and proposals to concentrate on just saving portions of the reef.

“I’m excited about this idea because the potential is there to give the whole reef a chance,” Harrison said.

The reef sustained the worst coral bleaching event on record in 2016, and international scientists have concluded that curbing greenhouse gas emissions is the only way to end coral bleaching.

“It is important to note that our calculations and modelling so far show that there is a limit to how much cooling you can achieve with regional marine cloud brightening. This technology only has the potential to help buy the reef time; it will not be enough to save the reef if drastic and rapid cuts are not made to global greenhouse gas emissions.”