With the world set to blow past 1.5°C of warming, researchers are increasingly studying possible methods of cooling the planet by modifying the atmosphere or the oceans. More geoengineering research is planned in 2025, such as projects aiming to make clouds reflect more sunlight and efforts to remove carbon dioxide from the atmosphere by tweaking ocean chemistry.

Such tests have long been controversial. Opponents of research on geoengineering – itself a loaded term – see it as a hubristic distraction from pressing efforts to slash greenhouse…