Major carbon sink may have vanished for a second year in a row
Record heat in 2024 caused ecosystems on land to emit nearly as much carbon dioxide as they took out of the atmosphere
By James Dinneen
25 July 2025
Vegetation like that in the Chapada das Mesas National Park, Brazil, is no longer removing as much CO₂ from the atmosphere
Pulsar Imagens/Alamy
Hot and wet weather in 2024 – the hottest, wettest year on record – caused ecosystems on land to emit nearly as much carbon dioxide as they took out of the atmosphere, according to a preliminary analysis. This is the second year in a row in which the land carbon sink has nearly vanished due to climate-related stressors, and would explain why 2024 saw a record jump in the concentration of CO₂ in the atmosphere.
The findings could also mean that the land carbon sink – which normally removes billions of tonnes of CO₂ from the atmosphere each year and is essential for meeting climate targets – is weakening decades earlier than expected. It remains unclear, however, if the past two years represent a lasting trend.
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“Everybody I’ve talked with who is working on this subject is very surprised,” says Guido van der Werf at Wageningen University in the Netherlands. “It was projected to be a weak sink, but now there’s hardly any sink.”
Forests, grasslands and other ecosystems on land take up CO₂ from the atmosphere as they grow. When they decompose or burn, this carbon is returned to the atmosphere. The uptake and release should generally be in balance. But over the past half century or so, these ecosystems have tended to take up more CO₂ than they have released, creating a carbon sink that varies in strength from year to year.
This tilted balance is thought to be due mainly to increased concentrations of CO₂ in the atmosphere fertilising plants, plus other factors like nutrient pollution and reforestation. But it isn’t expected to last forever because the climate consequences of rising CO₂ are catching up with the fertilisation effect. “We know the land carbon sink will diminish, but we don’t know how fast it will diminish,” says Van der Werf.
