In 2023 the world’s forests stopped acting as a carbon sink

“We cannot count on ecosystems to bail us out in the future.”

PHOTO Credit: Drought fuels wildfires in the Amazon, NASA.

At the recent International Carbon Dioxide Conference in Manaus, Brazil, scientists presented preliminary findings that in 2023 the world’s forests stopped acting as a carbon sink. An intense drought in the Amazon rainforest and record wildfires in Canada were part of the reason that forests and other land ecosystems emitted almost as much carbon dioxide as they removed from the atmosphere.

Usually, forests remove about one-quarter of the world’s annual CO₂ emissions from the atmosphere. But in 2023, that carbon sink collapsed, study co-author Philippe Ciais of the French research organisation the Laboratory for Climate and Environmental Sciences told Reuters.

As a result, in 2023, the growth rate of CO₂ in the atmosphere shot up by 86% compared to 2022. Yet CO₂ emissions — which come mainly from burning fossil fuels — only increased by between 0.1% and 1.1%. The explanation is that natural carbon sinks absorbed much less.

In 2023, land carbon sinks absorbed between 1.5 and 2.6 billion metric tons of CO₂, way less than the 9.5 billion metric tons in 2022. That is the lowest level since 2003.

Ciais also spoke to Le Monde:

“If this collapse were to happen again in the next few years, we risk seeing a rapid increase in CO₂ and climate change beyond what the models predict.”

Record warming in 2023

In their paper, the scientists write that, “record warming in 2023 had a strong negative impact on the capacity of terrestrial ecosystems to mitigate climate change”.

Stephen Sitch, a co-author and Chair in Climate Change at the University of Exeter, said to Reuters,

“Imagine your plants at home: If you don’t water them, they’re not very productive, they don’t grow, they don’t take up carbon. Put that on a big scale like the Amazon forest.”

The study is still in the process of peer review, but Reuters spoke to scientists who were not involved in the research, who said that the conclusions were sound.

Trevor Keenan is an ecosystem scientist at University of California, Berkeley. He was not involved in the study. “We cannot count on ecosystems to bail us out in the future,” he told Reuters.

Richard Birdsey of Woodwell Climate Research Center in the US was also not involved in the study. “This is a warning,” he told Reuters. “There’s a good chance that years like 2023 are going to be more common.”

New Scientist spoke to Scott Denning at Colorado State University, who was not involved in the study. “It’s pretty grim,” he said. “If there’s no more sink, then CO₂ will start to increase much faster.”

Denning told New Scientist that it is not yet clear whether the collapse of the land carbon sink in 2023 is a temporary response to an extremely hot year, or a more permanent collapse.

“But every time a hot episode wipes out part of the sink, or in this case all of the sink,” he told New Scientist, “it adds credence to the idea that the sink can’t be sustained in the long term.”

New Scientist reports that,

Driving these changes were 2023’s record high temperatures, which were mainly due to rising greenhouse gases and a shift to hotter El Niño conditions in the middle of the year. The team found that almost 30 per cent of the decline in the land carbon sink was due to net emissions in areas that saw the hottest 5 per cent of temperatures, as the heat stressed ecosystems and exacerbated drought and fire.

The Amazon tipping point

REDD-Monitor has written a series of posts based on scientific papers about the impact of the climate crisis on forests, and about the dangers of the Amazon rainforest tipping from a carbon sink to a carbon source.

I’m afraid it makes for extremely depressing reading. This post, for example, is from 2015 and is based on a paper in Nature titled “Long-term decline of the Amazon carbon sink”:

The solution, of course, is to leave fossil fuels in the ground. Massively reducing deforestation and forest degradation is also important. But continuing to promote the idea of trading reduced emissions from avoided deforestation against continued emissions from burning fossil fuels is just nuts.

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