A new study reveals that the carbon stored by plants globally is more transient and vulnerable to climate change impacts than previously understood. Led by Dr. Heather Graven of Imperial College London, the research shows that current climate models significantly underestimate how much CO2 is absorbed by vegetation annually and overestimate the duration it is retained, suggesting that carbon is released back into the atmosphere sooner than expected.
This indicates a need for rapid reduction in fossil fuel emissions and suggests limitations in the effectiveness of nature-based carbon removal strategies, such as large-scale tree planting. The study emphasizes that plants absorb and release carbon dioxide faster than previously thought, challenging the effectiveness of nature-based carbon removal strategies and underscoring the urgency to cut fossil fuel emissions to combat climate change. The research, led by an international team and published in the journal, reveals that existing climate models underestimate the amount of carbon dioxide (CO2) taken up by vegetation globally each year, while overestimating how long that carbon remains stored.
Dr. Graven, a Reader in Climate Physics in Imperial’s Department of Physics, stated: “Plants across the world are actually more productive than we thought they were.” However, while carbon is taken up by plants quicker than previously believed, it is also locked up for a shorter time, meaning carbon from human activities will be released back into the atmosphere sooner than 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.”
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.
The sparsity of sites with comprehensive measurements has made it challenging to accurately calculate global Net Primary Productivity.
Faster carbon cycling in plants
Plants’ productivity has been increasing since the early 1900s, and more CO2 is currently taken up by plants than is released back into the air, with approximately 30% of CO2 emissions from human activities stored in plants and soils each year.
However, the details of this storage and its future stability remain poorly understood. In this study, radiocarbon (C14)—a radioactive isotope of carbon—was combined with model simulations to provide valuable insights into how plants use CO2 at a global scale, unlocking crucial information about the interaction between the atmosphere and the biosphere. Radiocarbon is produced naturally, but nuclear bomb testing in the 1950s and 1960s increased the level of C14 in the atmosphere.
This extra C14 allowed researchers to measure how fast plants globally could take it up. By examining the accumulation of C14 in plants between 1963 and 1967, researchers assessed how quickly carbon moves from the atmosphere to vegetation and what happens to it once there. The results show that current, widely used models that simulate how land and vegetation interact with the atmosphere underestimate the Net Primary Productivity of plants globally and overestimate the storage time of carbon in plants.
Co-author Dr. Charles Koven from Lawrence Berkeley National Laboratory stated: “The observations show that the growth of plants at the time was faster than current climate models estimate it was. This implies that carbon cycles more rapidly between the atmosphere and biosphere than we have thought, and that we need to better understand and account for this more rapid cycling in climate models.”
The authors emphasize the need to improve theories about how plants grow and interact with their ecosystems and to adjust global climate models accordingly.
Co-author Dr. Will Wieder from the National Center for Atmospheric Research noted: “Scientists and policymakers need improved estimates of historical land carbon uptake to inform future projections. Our study provides critical insights into terrestrial carbon cycle dynamics, which can inform models used for climate change projections.”
The study’s authors include German physicist Ingeborg Levin, a pioneer in radiocarbon and atmospheric research, who passed away in February.
This research highlights the usefulness of radiocarbon measurements in addressing the complexities of the biosphere.
