Plants and trees ability to absorb carbon dioxide fell dramatically in 2023, due to increased heat stress in vegetation, a new study revealed.

A “low latency carbon budget analysis” reveals a large decline in the land carbon sink in 2023, according to a new academic paper.

A tree typically absorbs 25kg of CO₂ each year (although bamboo absorbs about a third more carbon than a tree) and globally trees absorb an estimated 7.6 gigatonnes of carbon, acting as a net carbon sink, removing greenhouse gases.

“In 2023, the CO2 growth rate was 3.37 +/- 0.11 ppm at Mauna Loa [in Hawaii], 86% above the previous year, and hitting a record high since observations began in 1958, while global fossil fuel CO₂ emissions only increased by 0.6 +/- 0.5%. This implies an unprecedented weakening of land and ocean [carbon] sinks, and raises the question of where and why this reduction happened,” the paper authored by Piyu Ke et al reported.

The study found that while ocean carbon sinks were working fine, the problem was on land, where multiple factors affect the amount of CO₂ plants can absorb, including droughts, fires and man-made factors like logging.

“Land regions exposed to extreme heat in 2023 contributed a gross carbon loss of 1.73 gigatonnes a year, indicating that record warming in 2023 had a strong negative impact on the capacity of terrestrial ecosystems to mitigate climate change,” the paper found.

As bne IntelliNews reported, trees were already “coughing not breathing” due to climate crisis stress, according to another earlier study. Trees are struggling to trap carbon dioxide in warmer, drier climates, meaning that they may no longer serve as a solution for offsetting humanity's carbon footprint as global warming accelerates, a study by Penn State university found.

“If the land carbon sink is decreased, it will be even harder (impossible?) to get CO₂ concentrations down,” says Lee Simons, a climatologist.

But the trees themselves are physically in danger as a result of the extreme temperatures. One of the consequences of global warming is more wildfires that run out of control.

Yakutia, a Republic in Russia’s Siberia, is currently dealing some of its worst wildfires ever, with over 350,000 hectares on fire forcing the regional authorities to declare a state of emergency. And last year’s extreme fires in Canada put 2.1 gigatonnes of CO₂ back in the atmosphere in 2023.

To put these numbers into context, the 2.1 gigatonnes added to the atmosphere by the Canadian wildfires is more CO₂ than is produced by any country in the world, other than the three biggest emitters of China (11.4 gigatonnes), US (5 gigatonnes) and Russia (2.8 gigatonnes). It is also about a third of all the carbon that is absorbed by all the threes on the planet each year. If the CO₂ emissions from the wildfires in the US, Russia and SE Asia that are currently burning are taken into account, then it appears a large proportion of the carbon dioxide that should be removed each year by trees is being returned to the atmosphere by burning trees.

This is before other factors are included. For example, the Amazon forest, the “lungs of the world”, suffered from a severe drought last year that also impeded plants’ ability to fix CO₂ and also accounted for a large fall in the carbon sink effect in 2023, according to Philippe Ciais, a climatologist with Laboratory of Science, Climate and the Environment (LSCE) at the Versailles Saint-Quentin en Yvelines University in France, that has raised similar concerns.

“The regions with the hot temperatures are losing the most carbon in 2010-22,” says Ciais. “Those losses were even higher in 2023, especially in the Tropics… Even if 2023 was a transition from a La Niña (good for carbon sinks) to a moderate El Niño, we see a sudden drop of the land carbon sink from extreme warming and Amazon mega-drought.”

“The decline of the northern sink was masked by recent good conditions in the Tropics absorbing CO₂, but in the coming years if this decline continues, we may see a rapid acceleration of CO₂ and global warming which was unforeseen in future climate models projections,” Ciais adds.

The findings of this research is worrying scientists as plants falling ability to fix carbon dioxide is not included in the models. It has already become clear that the climate models are wrong as global warming is already accelerating faster than the most pessimistic scenarios, partly due to their failure to take account of the warming affect owing to the removal of aerosols from the atmosphere in the last few years. Now burning tree and coughing tree factors will have to be added to the calculations.