The Warming Ocean: Uncovering Unexpected Benefits from Coral Reef Loss

The decline of coral reefs might come with unexpected advantages. Research suggests that this deterioration allows the oceans to absorb up to 5% more carbon dioxide by 2100, which may decelerate the buildup of this greenhouse gas in the atmosphere.

“If your primary concern is the CO2 concentration in the atmosphere, this could be viewed as a beneficial effect,” states Lester Kwiatkowski from Sorbonne University in Paris, France. However, he cautions that the loss of coral also leads to diminished biodiversity, jeopardizes fisheries, and heightens the vulnerability of coastal regions to rising sea levels.

The extent of global warming is heavily influenced by atmospheric CO2 levels. To date, land and oceans have collectively absorbed around half of the surplus CO2 we’ve emitted. Thus, elements that affect these so-called land or marine carbon sinks can significantly influence future climate scenarios.

Corals are often believed to sequester CO2 from seawater while they develop their calcium carbonate structures. In reality, this process—known as calcification—actually releases CO2 as a net byproduct.

“Corals typically take in inorganic carbon from the ocean in forms like carbonate and bicarbonate ions, converting them into calcium carbonate, which results in CO2 being expelled back into seawater.”

This suggests that if the growth of coral reefs slows or halts, there will be a reduction in CO2 emissions from these reefs, thereby allowing the ocean to absorb more of this greenhouse gas from the atmosphere—a factor currently absent from climate models.

Current studies indicate that coral reef calcification has already declined due to rising ocean temperatures, leading to extensive coral bleaching. Additionally, increased CO2 levels have caused ocean acidification, which complicates the formation of carbonate structures and can even trigger dissolution.

Kwiatkowski and his research team have published estimates detailing how corals are susceptible to warming and ocean acidification. They utilized computer models to project how these changes could affect marine carbon sinks under various emission scenarios. Their findings indicate that by 2100, the ocean may sequester an additional 1-5% more carbon, which could escalate to up to 13% by 2300.

This prediction may be conservative, as Kwiatkowski notes it overlooks additional factors contributing to coral reef degradation, such as overfishing and the spread of coral diseases.

Conversely, the research assumes that corals lack the capacity to adapt or acclimate. Chris Ju judge from the University of Hawaii at Manoa, who was not part of this study, remarks on this perspective.

“If we encounter the worst-case or medium-case outcomes outlined in this study, it portends significant destruction of coral reefs globally,” says Ju judge. “I believe the authors could arrive at different conclusions by considering potential adaptability in corals and other reef organisms under moderate levels of climate change.”

If Kwiatkowski’s team’s projections hold true, the amount of CO2 that leads to a certain degree of warming—the so-called carbon budget—may actually be larger than current estimates.

“Even if we’re facing dire outcomes, it’s critical to refine our understanding of the carbon budget to ensure its accuracy,” asserts Kwiatkowski.