Current Human Emissions on Path to Cause Mass Marine Extinction Event

Science, 28 April 2022

Under a high emissions scenario, the combination of ocean acidification, ocean warming and oxygen loss — especially in the polar oceans — will result in catastrophic marine species loss by 2300. The scale of loss would be on par with the five mass ocean extinction events in Earth’s past. Rapidly curbing global emissions to keep within the 1.5°C/2°C limit of the Paris Agreement could largely prevent this outcome, and reduce ocean extinction risk by 70%. In 2021, global oceans broke two long-term records: they reached both the highest temperatures, and the lowest levels of oxygen since human records began. As atmospheric temperatures rise, the ocean absorbs heat and forms a buoyant layer of warm water along its surface. Along with heating the upper layer itself, this mantle of warm water slows mixing with colder deeper layers, preventing oxygen-rich surface waters from cycling into the lower depths of the ocean. The formation of such low-oxygen zones reduces the available habitat for many species, forcing them to live closer to the surface in tighter groups, making them more subject to predation as well as marine heat waves. Such complex interactions and feedbacks will create massive shifts in species, and ultimately mass extinctions as available habitats decline; without rapidly declining emissions.