Canary IslandsBefore sunrise in a quiet village in Gran Canaria, an island off the coast of northwest Africa, a team of scientists shuffles along the port’s wooden boardwalk toward a row of nine containers floating in the ocean.

“Hurry up, it’s going to get light soon,” says one bleary-eyed researcher to another, as they submerge a hefty, cube-shaped device for measuring the activity of bioluminescent organisms into one container. “That will affect our readings.”

The thermoplastic polyurethane “mesocosms,” filled with 8,000 liters of Canarian seawater mixed with varying amounts of limestone—a greyish, carbonate rock with high levels of alkaline—were part of the world’s first scientific field experiment with ocean alkalinity enhancement; research was completed in October. Many scientists hope that this