As it left Townsville, Australia, in March, the converted ferry boat had a mobile scientific laboratory and a big fan on its deck in place of its usual load of automobiles and vans. The researchers anchored in a coral lagoon 100 kilometers offshore and then turned on the cone-shaped turbine, which blasted saltwater over the rear of the boat in a mist. What occurred next was a pleasant surprise: the plume rose into the sky after momentarily floating over the ocean's surface.
Brightening the Clouds
This mist machine, which resembles a jet engine, is at the heart of an experiment that, if successful, may help decide the Great Barrier Reef's destiny. Three hundred and twenty nozzles sprayed a cloud of nano-sized particles designed to brighten clouds and block sunlight, offering some relief for the coral colonies below. Sensors on the ferry, drones, and a second boat were deployed to track the plume as it moved upward.
Small Scale Experiment
The experiment was too small to have a major impact on the clouds. But, according to Daniel Harrison, an oceanographer, and engineer at Southern Cross University in Coffs Harbour, Australia, who is leading the research, preliminary results from field tests - which were shared exclusively with Nature - suggest that the technology may perform even better than computer models predicted. Harrison says, "We are now quite sure that we can get the particles up into the clouds." "However, we must still figure out how the clouds will react."
Harrison's experiment is the first field test of marine cloud brightening, one of several controversial geoengineering methods that scientists have investigated for decades in the lab. The research is motivated by the worry that humans will be compelled to influence the Earth's climate and weather systems to mitigate the worst effects of global warming in the future.
Coral Bleaching in Australia
For many Australians, that day came in 2017, when major coral bleaching and mortality occurred throughout most of the 2,300-kilometer Great Barrier Reef due to a marine heat wave. That disaster occurred just a year after another coral bleaching incident on the reef, home to over 600 kinds of coral and supporting an estimated 64,000 jobs in tourism and fishing. Warming seas, tropical storms, and predatory starfish have caused the reef to lose more than half of its coral between 1995 and 2017.
Some scientists in other countries are concerned about the research, partly because the Australian group hasn't published much about its findings. Last year, when news of the first experiment surfaced, environmentalists worldwide protested to the idea, and the details of the 2021 trial may draw similar criticism.
Local Adaptation to Climate Change
Because its use would be limited in geography and time, Harrison emphasizes that the cloud-brightening initiative is about local adaptation to climate change, not global geoengineering. It's also part of Australia's broader Reef Restoration and Adaptation Program (RRAP), which began last year with a budget of Aus$300 million (US$220 million) to research and develop strategies and technology to restore the country's reefs. Many suggestions, ranging from cloud brightening to the breeding of heat-tolerant corals, would be firsts for humans in the natural reef system.
According to ecological modeling, a large-scale intervention incorporating several techniques, including a fleet of mist machines, may extend the reef's life as governments strive to reduce greenhouse gas emissions. But, according to Cedric Robillot, executive director of the RRAP, today's objective is to figure out what is feasible in the actual world.
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