Some of the key components of Earth's climate system remain largely overlooked. Calcifying plankton—microscopic organisms that form hard shells—play a crucial role in regulating the planet's temperature by capturing carbon and transporting it through the ocean. However, as highlighted in a new review published in the journal Science, these organisms are insufficiently represented in climate models used to predict Earth's future. The study was conducted by an international team from the Institute of Environmental Science and Technology at the Autonomous University of Barcelona (ICTA-UAB, Spain).

The Role of Calcifying Plankton in Climate

The paper examines three main groups of calcifying plankton: coccolithophores, foraminifera, and pteropods. According to the authors, climate models often oversimplify or entirely omit these organisms, which can lead to an incomplete understanding of how the ocean responds to climate change.

When climate models fail to account for calcifying plankton, they may miss critical stages of the global carbon cycle. These organisms build tiny shells from calcium carbonate (CaCO₃), a substance that plays a key role in ocean chemistry. As plankton grow and die, carbon is transferred from the atmosphere into deeper ocean layers.

This process, known as the oceanic carbon pump, helps stabilize Earth's climate over long periods. It also influences the chemistry of seawater and contributes to the formation of sediments that scientists use to study past climates.

“Plankton shells are small, but together they shape the chemistry of our oceans and the planet’s climate,” notes Patricia Ziveri, ICREA research professor at ICTA-UAB and lead author of the study. “If we leave them out of climate models, we risk missing fundamental processes that determine how the Earth system responds to climate change.”

Limitations of Current Models

The researchers emphasize that most of the calcium carbonate produced by plankton does not reach the ocean floor. A significant portion dissolves in the upper water layers—a process called surface dissolution. This is driven by biological activity, predation, particle aggregation, and microbial respiration.

Surface dissolution significantly alters ocean chemistry, yet this process is barely considered in major Earth system models (such as CMIP6) used for global climate assessments. Without accounting for it, models may inaccurately estimate carbon movement in the ocean and the system’s response to ecological stressors.

Diversity and Vulnerability of Plankton

The study also notes that different groups of calcifying plankton behave in distinct ways. Each has unique characteristics that affect their distribution, role in marine ecosystems, and sensitivity to climate change.

Coccolithophores are the largest producers of CaCO₃, but they are especially vulnerable to ocean acidification because they lack specialized mechanisms to remove excess acidity from their cells. Foraminifera and pteropods possess such mechanisms, but face other risks, including declining oxygen levels and rising water temperatures. Together, these organisms determine how carbon is stored and processed in the ocean, and treating them as a single group oversimplifies the ocean’s response to climate impacts.

The Need for New Data and Approaches

The authors call for urgent measurement of how much calcium carbonate each plankton group produces, dissolves, and exports to deeper waters. Including this data in climate models, they argue, will improve predictions of ocean-atmosphere interactions, long-term carbon storage, and the interpretation of sediment records used to reconstruct Earth’s climate history.

“If we ignore the smallest inhabitants of the ocean, we may miss important climate dynamics,” says Dr. Ziveri. “Integrating calcifying plankton into climate models can provide more accurate forecasts and a deeper understanding of how ecosystems and societies may be affected.”

The researchers conclude that addressing these knowledge gaps is essential for developing a new generation of climate models that more accurately reflect the biological complexity of the oceans.