Study finds plants store carbon for shorter periods than thought

The carbon stored globally by plants is shorter-lived and more vulnerable to climate change than previously thought, according to a new study.

The findings have implications for our understanding of the role of nature in mitigating climate change, including the potential for nature-based carbon removal projects such as mass tree-planting.

The research, carried out by an international team led by Dr. Heather Graven at Imperial College London and published in Science, reveals that existing climate models underestimate the amount of carbon dioxide (CO₂) that is taken up by vegetation globally each year, while overestimating how long that carbon remains there.

Dr. Graven, Reader in Climate Physics in Imperial's Department of Physics, said, "Plants across the world are actually more productive than we thought they were."

The findings also mean that while carbon is taken up by plants quicker than thought, the carbon is also locked up for a shorter time, meaning carbon from human activities will be released back into the atmosphere sooner than previously predicted.

Dr. Graven added, "Many of the strategies being developed by governments and corporations to address climate change rely on plants and forests to draw down planet-warming CO₂ and lock it away in the ecosystem.

"But our study suggests that carbon stored in living plants does not stay there as long as we thought. It emphasizes that the potential for such nature-based carbon removal projects is limited, and fossil fuel emissions need to be ramped down quickly to minimize the impact of climate change."

Using carbon

Until now, the rate at which plants use CO₂ to produce new tissues and other parts globally—a measure known as Net Primary Productivity—has been approximated by scaling up data from individual sites. But the sparsity of sites with comprehensive measurements means it has not been possible to accurately calculate Net Primary Productivity globally.

Plants' productivity has been increasing since the early 1900s and more CO₂ is currently taken up by plants than is released back to the air. Researchers know that approximately 30% of CO₂ emissions by human activities are therefore stored in plants and soils each year, reducing climate change and its impacts.

However, the details of how this storage happens, and its stability into the future, are not yet well understood.

In this study, radiocarbon (¹⁴C)—a radioactive isotope of carbon—was combined with model simulations to understand how plants use CO₂ at a global scale, unlocking valuable insights into the interaction between the atmosphere and the biosphere.