Tiny ocean organisms missing from climate models may hold the key to Earth’s carbon future

The ocean’s smallest engineers, calcifying plankton, quietly regulate the Earth’s thermostat by capturing and cycling carbon. However, a new review published this week in Science by an international team led by the Institute of Environmental Science and Technology at the Universitat Autònoma de Barcelona (ICTA-UAB) (Spain) finds that these organisms, coccolithophores, foraminifers, and pteropods, are oversimplified in the climate models used to predict our planet’s future. 

By omitting these plankton, current models may underestimate key processes in the global carbon cycle and the ocean’s capacity to respond to climate change. Calcifying plankton build minute shells of calcium carbonate (CaCO₃), a critical component of the ocean’s carbon cycle. These organisms influence seawater chemistry and facilitate the transfer of carbon from the atmosphere to the deep ocean. This “carbon pump” helps regulate Earth’s climate and influences everything from ocean chemistry to the fossil record.  

“Plankton shells are tiny, but together they shape the chemistry of our oceans and the climate of our planet,” said Patrizia Ziveri, ICREA research professor at ICTA-UAB and lead author of the study. “By leaving them out of climate models, we risk overlooking fundamental processes that determine how the Earth system responds to climate change.” 

But as the authors show, much of this calcium carbonate never reaches the seabed. Instead, a large fraction dissolves in the upper ocean—a process known as “shallow dissolution.” Driven by biological interactions like predation, particle aggregation, and microbial respiration, shallow dissolution profoundly alters the ocean’s chemistry, but remains largely absent from key Earth System Models (e.g. CMIP6) that inform global climate assessments. 

The study highlights the unique traits of different calcifying plankton groups, which determine their geographic distribution, ecological role, and vulnerabilities. Coccolithophores, the main producers of CaCO₃, are especially sensitive to acidification, as they lack specialized pumps to remove acidity from their cells. Foraminifers and pteropods do, but they face different pressures, from oxygen loss to warming waters. Together, these groups shape the fate of carbon in the ocean. Ignoring their diversity risks oversimplifying how the ocean responds to climate stressors. 

The paper calls for urgent efforts to better quantify group-specific production, dissolution, and export of calcium carbonate, and to incorporate these dynamics into climate models. Doing so would allow for more accurate projections of ocean–atmosphere feedbacks, carbon sequestration, and even the interpretation of sediment records used to reconstruct past climates. 

“If we ignore the ocean’s smallest organisms, we might miss important climate dynamics”, says Dr. Ziveri. “Integrating calcifying plankton into climate models could offer sharper predictions and deeper insights into how ecosystems and societies may be affected.” 

The researchers conclude that addressing these knowledge gaps is critical to developing a new generation of climate models that better capture the biological complexity of the oceans.