Could "Cloud Brightening" Save the Great Barrier Reef From Climate Change?

To put it gently, the Great Barrier Reef has not had a great couple of years. A 2016 heat wave killed 29 percent of the reef’s coral, and the pace of climate change shows no sign of slowing. But one scientist’s outside-the-box idea may buy the Great Barrier Reef a little more time — and it’s a really big idea.

Daniel Harrison, Ph.D., a research fellow at the Sydney Institute of Marine Science, proposes that making the clouds over the Great Barrier Reef brighter and more reflective would bounce more sunlight away from the Earth. This, he says, could help keep the water around the reef from warming quickly and bleaching the coral. To achieve this inconceivably huge task, Harrison proposes spraying seawater up at the clouds, where the salt molecules from the water would encourage water to condense around them. Theoretically, the higher salt content in the clouds would make them brighter than your average clouds. And since atmospheric water droplets need to condense around something to form clouds, Harrison says the salt in seawater — which will leave the water behind as giant fans blow it through the air — will provide the particles necessary for clouds to form.

“Over the land there’s a lot from dust and everything,” Harrison tells China’s state-run news agency Xinhua. “Over the ocean they’re largely formed by sea salt. The idea is that we’d take sea water and we’d spray it out as these nano-sized droplets and they evaporate leaving the sea salt crystal behind.” It sounds ambitious, but Harrison explains that this urgent matter calls for creative solutions.

“[Losing the reef] isn’t something that’s going to happen in future generations, it’s right now in this generation if we don’t act now,” he told The Sydney Morning Herald on Monday. “It’s truly scary.”

He’s not the only one who thinks the reef is in immediate danger, and he’s not the only one desperately looking for answers.

While a paper published in April in PLOS Genetics suggests that some of the Great Barrier Reef’s coral is evolving to survive warmer waters, climate change may be progressing too rapidly for the reefs to keep up. Another paper published in April in Proceedings of the National Academy of Sciences showed evidence that scientists could use CRISPR/Cas9 gene editing to enhance beneficial traits in coral, but that team’s results were mixed, and it’s not clear whether the genetic changes would remain in future generations once the altered coral got released into the wild. So-called “coral in-vitro fertilization” has shown promising early results, but it won’t help stop future bleaching and die-offs.

Since nobody has come up with a home run answer to the threat posed by warming ocean waters that are driven by climate change, even strange ideas like cloud brightening are receiving serious consideration. Harrison represents a growing body of scientists who argue that geoengineering projects like this may be the best hope for saving the Great Barrier Reef.

In a paper published in June 2017 in the journal Earth’s Future, a team of atmospheric scientists proposed that cloud brightening could be feasible, but also emphasized that scientists need to devise controlled experiments to test the strategy.

“A major, unsolved question in climate science is: How much do aerosol particles cool the planet?” first author Rob Wood, a professor of atmospheric sciences at the University of Washington, said in a statement. By “aerosol,” he means particles sprayed into the air — as in Harrison’s seawater idea. “A controlled test would measure the extent to which we are able to alter clouds, and test an important component of climate models,” said Wood.

One of the main issues that Wood and his colleagues identified is that it’s hard to measure the effectiveness of aerosol cloud brightening, since global climate research can’t adequately untangle aerosol cooling effects from other factors. For this reason, they’ve called for small-scale controlled experiments to see just how much a solution like cloud brightening could really change things.

With the effects of climate change racing forward unabated, even strange solutions deserve consideration, and that’s exactly what will happen when Harrison presents his plan to experts in Queensland on Tuesday.