No fish, whales, or plankton: An ocean without life will absorb less carbon emissions and accelerate climate change

The ocean plays a critical role in regulating Earth’s climate. It is a massive carbon store that absorbs about 25 percent of human-caused emissions and thus helps maintain a relatively low CO2 level in the atmosphere. But what would happen if all marine life – from the tiniest plankton to the largest whales – disappeared? A recent study delves into this extreme scenario to uncover the crucial role that ocean biology plays in mitigating climate change.

Marine life helps store carbon in the ocean. Plankton and other living organisms consume carbon near the ocean surface, and when they die, they sink to the deep ocean, bringing carbon from the atmosphere with them. This process is called the biological carbon pump.

But what would be the consequences if all marine life disappeared?

Researchers Jerry Tjiputra, Damien Couespel, and Richard Sanders, all affiliated with NORCE and the Bjerknes Centre, used the Norwegian Earth System Model (NorESM) to simulate exactly this in their study 'Marine ecosystem role in setting up preindustrial and future climate' published in Nature Communications.

In one simulation experiment, the researchers kept things as realistic as possible, and in the other, they removed all marine life. As expected, the elimination of marine life led to a significant increase in atmospheric CO2 levels, by approximately 50 percent.

– But the simulation showed that in a scenario where all marine life is eradicated, land ecosystems will absorb about half of the carbon that the ocean cannot take up without marine life, says researcher Damien Couespel.

– We have long understood that the biological carbon pump plays a crucial role in keeping atmospheric CO2 levels low. However, most studies have overlooked the interaction with Earth's ecosystems. Our research suggests that land ecosystems compensate if marine life is eradicated and the ocean’s ability to absorb CO2 is thus limited, says Jerry Tjiputra, lead author of the study.

To understand the significance of marine life for the ocean’s uptake of human-caused emissions, the researchers also conducted simulation experiments where they first simulated Earth's climate before humans began emitting large amounts of CO2 (pre-industrial climate, before 1850) and compared it with a simulation of future emissions.

This was done both with and without marine life.

– In all cases, much more CO2 will remain in the atmosphere if all marine life were removed. This is because, without living organisms consuming carbon at the ocean surface, the carbon content at the ocean surface is much higher. This limits the ocean's ability to absorb more CO2, explains Jerry Tjiputra.

– Our results thus challenge the paradigm that the ocean's carbon uptake is mainly driven by physical and chemical processes, rather than biological ones. An ocean without life would weaken its ability to absorb carbon emissions, says Damien Couespel.

In this extreme scenario, we would experience faster and more intense warming and a potential to trigger other processes that can further amplify warming.

Tjiputra and his colleagues acknowledge that zero life in the ocean is an extreme scenario to explore, but he believes the study has provided insights.

– We have learned that marine and terrestrial life work together to regulate our climate and that marine life is a key player in shaping the course of climate change. Our research clearly underscores that there is a link between the protection of marine ecosystems and combating climate change. A healthy ocean buys us time. Damage to marine ecosystems can significantly accelerate human-caused climate change and further challenge our ability to meet the goals in the Paris Agreement. Preserving the function of marine ecosystems is essential for mitigating climate change and its associated risks, says Tjiputra.