The fog was neither subtle nor slow. It did not emanate gradually from the sea or roll gently down the slopes of the nearby islands. It erupted into the air with all the drama of a volcanic-ash plume. Yet, for all that, its source was quite modest: a grid of nozzles, about 20 feet wide, stationed on the back of a ship.

On a hot February morning, that ship and two smaller companion barges — nicknamed Big Daddy and the Twins — roamed a bay within the Palm Islands cluster, off the northeastern coast of Australia. Each pumped seawater aboard, pressurized it and sprayed it into the air through hundreds of tiny nozzles arrayed on metal frames. Dense plumes of fog billowed from all three vessels, forming long white strands that eventually converged into a seamless cloak. Daniel Harrison — an engineer, pilot and oceanographer based at Southern Cross University’s National Marine Science Center — surveyed the scene from the large ship’s observation deck, one hand on his wide-brimmed brown felt hat to keep it from flying away. It was the most successful test of the technology to date, he said.

Since 2016, Harrison and his colleagues have been investigating whether it is possible to reduce coral bleaching in the Great Barrier Reef by altering the weather above it. As the planet heats up, unusually high ocean temperatures are stressing corals around the world, forcing them to eject their symbiotic partners: the photosynthetic single-celled algae that live in their tissues and provide them with much of their sustenance. Theoretically, machine-generated fog and artificially brightened clouds can shade and cool the water in which corals live, sparing them much of that stress.

Not far behind the primary fogger on the big ship stood a pair of cloud-modifying machines known as the cannons. From a distance, each tubular white contraption resembled a jet engine angled toward the sky. Up close, you could see that they were mostly hollow, outfitted on one end with a large fan and on the other with a ring of torpedo-shaped manifolds, each of which supported nearly 100 small metal nozzles. When the scientists switched them on, a series of squat, square air compressors began to groan and shake, like washing machines pushed to their breaking point. This time, seawater pumped onboard was combined with highly pressurized air before being expelled through the nozzles. The result was a fine white mist that burst from the cannons at more than 60 miles per hour. As the wind lifted the briny spray into the air, it intermingled with low-lying clouds, making them more reflective.

Harrison’s project is essentially a highly localized version of geoengineering: the deliberate modification of the planet to counteract climate change. When Harrison began his undergraduate studies in the late 1990s, geoengineering was still largely taboo in the scientific community. In a paper that considered the history of such research, the climate scientist Stephen Schneider recalled that even the idea of including a single chapter on geoengineering in a 1992 National Research Council report resulted in “serious internal and external debates.” The physicist David Keith, now a prominent figure in the field, remembers colleagues in the ’90s telling him that pursuing geoengineering might tarnish his reputation and derail his career. Not much changed in the subsequent two decades, though there were some high-profile geoengineering blunders.