Throughout most of Earth's history, scientists have observed the gradual breakdown of rocks acting as the planet's natural temperature regulator. Rainwater absorbs carbon dioxide (CO2) from the atmosphere and then falls onto exposed rocks, slowly dissolving them. The carbon and minerals released travel to the oceans, where they form shells and limestone reefs. These materials lock carbon deep within the seafloor for millions of years.

There have been times when the entire Earth froze, from the poles to the equator. Rock weathering alone cannot account for these“snowball Earth” events, meaning other factors must have played a role. The study was published in the journal Science.

Clue From How the Ocean Stores Carbon

As atmospheric CO2 levels rise and the planet warms, more nutrients like phosphorus are washed into the seas. These nutrients feed algae blooms, which absorb carbon through photosynthesis. When the algae die, they sink to the seafloor, carrying carbon with them.

However, in warmer conditions, the rapid growth of algae causes a drop in oxygen levels in the water. With less oxygen, phosphorus is recycled instead of being buried in sediments. This creates a feedback cycle: more nutrients lead to more algae, which decompose and use up even more oxygen, releasing more nutrients in turn. At the same time, a lot of carbon is stored in marine sediments, which can help cool the planet.

Climate Regulation

Researchers Hülse and Chris Ridgwell have created a detailed computer model of Earth's climate that includes these complex ocean interactions. The research suggests that when atmospheric oxygen levels were lower, as they were in Earth's distant past, these nutrient feedbacks were stronger and might have driven the severe ice ages found in early geological records.

Today, as humans continue to add CO2 to the atmosphere, the planet is warming. According to the model, this warming may eventually lead to a cooling overshoot in the distant future. However, this effect would likely be less intense now, as modern oxygen levels reduce the strength of these nutrient feedbacks.

The focus is on reducing ongoing warming. Earth may naturally cool over time, but not quickly enough to protect us today.

The study was supported by the MARUM-based Cluster of Excellence 'The Ocean Floor – Earth's Uncharted Interface'. Hülse now plans to use the model to study how the Earth has sometimes recovered surprisingly quickly from past climate changes and how the ocean floor has played a role in those recoveries.

MENAFN03112025007385015968ID1110284880