Carbon Sinks in the Carbon Cycle

Aaron Fisher | April 25, 2025

Much like water, carbon follows a cycle through the environment. Burning fossil fuels emits CO₂, it moves through the air, and is taken up by plants. As scientists study the global carbon cycle there is ample evidence that Mother Nature is offsetting and absorbing some of the additional CO₂ that is emitted from burning fossil fuels.

However, we are also seeing some alarming signs from the global carbon cycle. Simply put the environment is out of whack and seems to be absorbing less CO₂ not more.

Changing the Global Carbon Cycle

“In 2023, the hottest year ever recorded, preliminary findings by an international team of researchers show the amount of carbon absorbed by land has temporarily collapsed. The final result was that forest, plants and soil – as a net category – absorbed almost no carbon.” (The Guardian). If the environment starts absorbing less CO₂ that leaves more in the atmosphere. Atmospheric CO₂ pushes the global balance further away from normal, exacerbating climate change.

A paper published in July found that while the total amount of carbon absorbed by forests between 1990 and 2019 was steady, it varied substantially by region. The boreal forests – home to about a third of all carbon found on land—stretching across Russia, Scandinavia, Canada and Alaska—have seen a sharp fall in the amount of carbon they absorb, down more than a third due to climate crisis-related beetle outbreaks, fire and clearing for timber. Again less absorption of CO₂ means more in the atmosphere.

Trees Being Less Valuable

In diving deeper on the natural processes (and how they are changing), some researchers are looking into the value of trees versus other natural elements.

A research team, coordinated by Yinon Bar-On (California Institute of Technology), found that around 35 gigatons of carbon were sequestered on Earth’s surface between 1992 and 2019. This accumulation of terrestrial carbon has increased by 30% over the last decade, from 0.5 gigatons per year to 1.7 gigatons per year. Yet, vegetation, mainly forests, accounts for only 6% of these carbon gains. Until now, forests were considered to be the main carbon sinks. In reality it’s soil, bodies of water, and wetlands that are serving as the largest carbon sinks.

However, disturbances linked to climate change or human activities—fires, deforestation, etc.—have made trees increasingly more vulnerable and now, in certain situations, they could emit almost as much carbon as they accumulate. Nevertheless, they remain important carbon stocks that need to be protected.

As we look towards managing the carbon cycle, specifically CO₂, we will need to prioritize what has and continues to work. Trees are part of this solution, but it seems they may not be the climate-saving panacea that is being marketed to us.