Lala Kounta still remembers 2020, when the waters off the coast of Senegal where she grew up turned unusually warm, triggering a toxic algal bloom that sickened hundreds of fishermen. That personal reckoning with marine catastrophe set her on a new research path—one that has now revealed a sobering truth about one of climate science's most controversial ideas: solar geoengineering could shield 25 to 75 percent of the world's oceans from marine heat waves, leaving vast stretches of sea still dangerously exposed.
The findings, published in Environmental Research: Climate by researchers at Michigan State University, arrive as ocean heat waves grow increasingly devastating. These underwater infernos are longer and more frequent than they were a century ago, and their impacts ripple through ecosystems and economies with startling speed. When high ocean temperatures struck off southern Chile in 2016, a toxic algal bloom wiped out 100,000 metric tons of salmon and trout—the largest fish farm mortality ever recorded. Thirty years of warming has killed more than half the living coral in Australia's Great Barrier Reef. A single marine heat wave can cost billions of dollars. From 2014 to 2016, a massive warming event off the U.S. West Coast starved sea lions and seabirds as their food sources fled to cooler waters.
Kounta, a physical oceanographer and postdoctoral scholar working with professor Phoebe Zarnetske in MSU's Ecology, Evolution and Behavior Program, understood that conventional climate solutions were moving too slowly. This prompted her team to examine a more radical proposal: stratospheric aerosol injection, a form of solar geoengineering that would use planes to release sun-blocking particles—like sulfur dioxide—high into the stratosphere. The concept mimics what volcanoes do naturally. When Mount Pinatubo erupted in the Philippines in 1991, it launched millions of tons of sulfur dioxide skyward, where the particles reflected incoming sunlight and temporarily cooled the planet by roughly half a degree Celsius for two years.
Using computer simulations, Kounta and her collaborators modeled marine heat waves under scenarios with and without solar geoengineering. The results underscore both the urgency and the limitations of the approach. Without intervention, ocean temperatures are projected to rise by 1 degree Celsius by 2069, with marine heat waves becoming hotter and longer across 97 percent of the world's oceans. But solar geoengineering wouldn't solve this problem uniformly. While the technology could cool some regions substantially, the unequal distribution of benefits means that millions of people dependent on fisheries in certain areas would remain vulnerable.
The National Academies has issued three reports in the past 30 years calling for more research into solar geoengineering's consequences, though most studies have focused on atmospheric warming rather than ocean impacts. Zarnetske and Kounta's work fills a critical gap, forcing the climate community to confront a hard reality: even technological interventions come with trade-offs, and some communities may be left behind. The research doesn't argue for or against solar geoengineering—it simply lays bare what it could and couldn't do. As marine heat waves intensify and coastal livelihoods hang in the balance, policymakers will need to wrestle with whether partial protection is better than none, and who gets to decide which oceans matter most.