Anthropogenic climate change is altering the living conditions in the ocean more dramatically than in the past 50 to 300 million years. The oceans are becoming warmer as they absorb more than 90 percent of the heat trapped in the atmosphere by greenhouse gases; at the same time they absorb large amounts of carbon dioxide, which chemically react with constituents of seawater, making the oceans more acidic.
But that’s not all: for various reasons, warming oceans store less oxygen. In other words, they gradually lose their lifeblood. But organisms need to breathe so that their bodies can produce energy – and the warmer the oceans become, the greater their oxygen requirements become. At the AWI, we discovered that the ability to supply the body with sufficient oxygen is subject to a certain limit, which varies by species. If this limit is exceeded, the cardiovascular system collapses.
For the past several years, biologists at the AWI have been investigating how marine organisms’ energy requirements have changed in the wake of climate change, how large their pH, temperature and oxygen tolerances are, and what behaviours could enable them to adapt to the new environmental conditions. To date, it appears that the large majority of marine life is fleeing the heat as far as geographically possible. Around the globe, species are shifting their habitats polewards or to greater depths. The increasing lack of oxygen in the seas simultaneously reduces the number of safe havens remaining to them. Increasing ocean acidification puts organisms under additional pressure. Further, these three climate impacts are mutually reinforcing. Accordingly, experts refer to them as the ‘deadly trio’ that are now drastically reducing marine life, on a scale not seen since the mass extinctions of Earth’s distant past.