Are Earth's carbon sinks collapsing?

Scientists fear that as it heats up, the planet is losing its natural ability to absorb CO2 through oceans, forests and soil

- Patrick Greenfield

It begins each day at nightfall. As the light disappears, billions of zooplankton, crustaceans and other marine organisms rise to the ocean surface to feed on microscopic algae, returning to the depths at sunrise. The waste from this frenzy -Earth's largest migration of creatures - sinks to the ocean floor, removing millions of tonnes of carbon from the atmosphere each year.

This activity is one of thousands of natural processes that regulate the Earth's climate. Together, the planet's oceans, forests, soils and other natural carbon sinks absorb about half of all human emissions. But as the Earth heats up, scientists are concerned that those crucial processes are breaking down. In 2023, the hottest year ever recorded, preliminary findings by an international team of researchers show the amount of carbon absorbed by land temporarily collapsed. The final result was that forest, plants and soil - as a net category-absorbed almost no carbon.

There are warning signs at sea, too. Greenland's glaciers and Arctic ice sheets are melting faster than expected, which is disrupting the Gulf Stream ocean current and slows the rate at which oceans absorb carbon.

Melting sea ice is exposing algaeeating zooplankton to more sunlight -a shift scientists say could keep them in the depths for longer, disrupting the vertical migration that stores carbon on the ocean floor.

"We're seeing cracks in the resilience of the Earth's systems. We're seeing massive cracks on land - terrestrial ecosystems are losing their carbon store and carbon uptake capacity, but the oceans are also showing signs of instability," Johan Rockström, director of the Potsdam Institute for Climate Impact Research, told an event at New York Climate Week in September. "Nature has so far balanced our abuse.