Why world's forests might lose their ability to absorb carbon?

The world's ecosystems could become unbalanced. This was warned by the journal Nature after a study led by the Center for Ecological Research and Forestry Applications (CREAF) together with the University of Antwerp (Belgium).

Behind this threat would be a phenomenon known as carbon sequestration, which is the difference between the CO2 that ecosystems capture and release into the atmosphere.

If carbon sequestration were to become unbalanced, it would cause abrupt changes. For example, forests in the Mediterranean would become scrub without the ability to return to their original form.

The study, published today (Wednesday, 22 February 2023) in Nature, found the regions most at risk typically have less forest cover and more cropland, are warmer and have experienced greater rises in temperature, which could be related to an increase in extreme weather events, such as heatwaves and cold snaps. The areas identified as most at risk include the Mediterranean Basin, Southeast Asia and the west coasts of North and Central America.

Unstable carbon storage

The team of researchers who conducted the study worked with global data on the net production of ecosystems between the years 1981 and 2018, and one of the conclusions they reached was that the areas most at risk of destabilization are those with the least forests and more crops.

A warm climate and increases in the variability of its temperatures, such as heat and cold waves, are also points of great influence.

The territories that are compatible with these characteristics are the Mediterranean, the eastern part of Eastern Africa, the western coasts of North America, Central America, India, Pakistan and Southeast Asia.

Ecosystems to decrease more

One of the co-authors of the study, Marcos Fernández, also warned that the areas at greatest risk could have a tendency for the stability of their ecosystems to decrease more and more due to the memory they adopt.

However, territories such as the Amazon, central and northern Europe have increased their capacity to sequester carbon.

"In the case of the Amazon, we see specifically that, although it has lost carbon during the study period, it loses less and less because the system is now less variable than before," adds Josep Peñuelas, research professor at CREAF.

That is why, ultimately, the ability to predict the carbon cycle of ecosystems is key in the fight against climate change.

Although it is not yet clear whether these abrupt changes in nature will bring about changes in the climate or in the capacity of plants to sequester carbon, the certainty is that destabilization can occur in large regions of the biosphere.

Highest rates of carbon sequestration

"This makes predictions more difficult because variability increases a lot," says Jordi Sardans, co-author of the study and CREAF researcherAnother of the results obtained by the scientists showed that the highest rates of carbon sequestration occur in regions with intermediate biodiversity.

Meanwhile, in places where biodiversity is very high, such as the tropics, this capacity is lower.

Why does this happen?

The research suggests that the positive effect of biodiversity on the decomposition and respiration of ecosystems could interfere with the positive effect of photosynthesis, a situation that would not occur in other ecosystems.

Global variation

While several regions are at risk of abrupt changes in their landscapes, there are parts of the world where carbon absorption levels are consistent and ecosystem collapse is less likely as a result of carbon fluctuations.

This includes the tropical forests of the Amazon, and parts of central and northern Europe, where carbon absorption capacity has increased.

However, the researchers warn that regions such as the Amazon face other climate threats, such as future shifts in regular patterns of rainfall.

The scientists say these global variations could make it harder to predict the global impact of schemes to absorb carbon, such as planting trees, in helping the world reach carbon net zero.

Dr McGuire said: “Ecosystems on land currently absorb almost one-third of the carbon emissions created by humans. If they start to absorb less carbon, the earth’s natural ability to curb climate change diminishes. This means we may need to cut human-made carbon emissions even faster than we had previously thought.”

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