Increased CO2 uptake by the ocean

The ocean takes up three times as much CO₂ as in 1960. The main reason is more CO₂ in the air. According to a new report, emissions have not stopped rising.

Together with vegetation on land, the ocean still takes up about half of all CO₂ emitted to the atmosphere. While this uptake reduces the temperature rise on Earth, it may affect life in the ocean.

"The most dire consequence is that the ocean gets more acidic," says Are Olsen, professor at the Geophysical Institute at the University of Bergen and leader of the carbon system research at the Bjerknes Centre.

Olsen is one of the researchers behind the global carbon budget, presented at the COP meeting in Azerbaijan today. Ocean acidification is know for harming corals and similarly makes it more difficult for many plankton species to build their calcium carbonate shells.

"This may contribute to reducing ocean biodiversity, and in the worst case productivity," says Are Olsen. "Plankton is the basis for marine ecosystems."

According to the new report, the top of the emission curve has not yet been reached. By the end of 2024, CO₂ emissions are expected to be 0.8 percent above those of 2023. While emissions in the US and the EU are expected to go down, those of China are assumed stable, while emissions in India increase.

Oceans and forests contribute to annual variations

During the last decade, emissions of CO₂ have generally increased, while emissions due to changes in land use have decreased. As a total this has led to stable emissions for the period. In 2024 both types of emissions are expected to increase.

"Last year's oceanic uptake was higher due to El Niño," says Are Olsen.

The longtime increase in the atmospheric CO₂ content is caused by anthropogenic emissions, but from one year to the next, natural variations contribute. On top of variations in the global economy and use of energy, changes in emissions are tied to weather and conditions in the oceans.

Most important for variations in atmospheric CO₂ content from year to year is the fluctuation between El Niños and La Niñas in the tropical Pacific. After a La niña in 2021–2022 El Niño conditions prevailed in 2023–2024. This has influenced the uptake of CO₂ both at sea and on land.

That the ocean takes up CO₂ does not mean that such uptake occurs in all ocean regions. While the Nordic Seas and the Southern Ocean are important uptake regions, CO₂ is released from the ocean to the atmosphere in other regions, like off the west coast of South America, where El Niños occur.

During an El Niño, the outgassing of CO₂ in this region is reduced. This increases the net uptake of the global ocean.

El Niños are also associated with less rain in large parts of the world. Forest fires in Canada and an intense drought in Brazil in 2023 and 2024 exacerbated CO₂ emissions from ruined forests.

The reduction in the forests' uptake of CO₂ was greater than the increased uptake by the ocean. This led to a significant increase in the atmospheric CO₂ concentration in 2023.

Need to cut emissions

The CO₂ content in the atmosphere is now fifty percent higher than before the industrial revolution. If emissions continue at the present level, the amount of CO₂ we can emit within the 1.5 degree target will be used up in six years.

"Most dream of a magic technology that will allow us to suck up CO₂ from the air. But I do not think this will be achievable on the scale needed before it is too late," says Are Olsen.

The carbon capture and storage technology is still at the exploration stage. As of today carbon corresponding to one millionth of the fossile fuel emissions can be captured.

From year to year emissions now increase less after growing steeply in 2000–2010. The average growth was then 2–3 percent per year, mainly due to a growing economy in China. Now Chinese emissions have leveled off, while emissions in India increase. 

"As a global society we must help people skip the petroleum age," says Are Olsen. "We must use resources and technology to build an alternative energy supply rather than get rich by letting them buy oil and gas."

He expresses optimisms over the growth in alternative forms of energy, with investments in solar and wind power and electric cars.

"I think we can do it," he says. "The question is whether we will manage to turn the curve fast enough."

Reference

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More graphs from the Global Carbon Budget are available here.