A new study shows that carbon stored by plants around the world is more volatile and vulnerable to the impacts of climate change than previously thought. Led by Dr Heather Graven of Imperial College London, the research shows that current climate models significantly underestimate the annual CO2 uptake by vegetation and overestimate the duration of storage, suggesting that carbon is being released back into the atmosphere sooner than expected. This highlights the need for rapid reductions in fossil fuel emissions and suggests limitations in the effectiveness of nature-based carbon removal strategies such as large-scale tree planting.
New research suggests that plants absorb and release carbon dioxide faster than previously thought, challenging the effectiveness of natural carbon removal strategies and underscoring the urgent need to cut fossil fuel emissions to combat climate change.
Global carbon stored by plants is more short-lived and vulnerable to climate change than previously thought, according to a new study. These findings have significant implications for our understanding of nature’s role in mitigating climate change, particularly for nature-based carbon removal projects such as mass tree planting initiatives.
The study, conducted by an international team led by Dr. Heather Graven at Imperial College London and published in Scienceshows that existing climate models estimate the amount of carbon dioxide (CO2) taken up by vegetation worldwide each year, although the duration of the carbon’s stay there is overestimated.
Dr Graven, a lecturer in climate physics in the Department of Physics at Imperial College, said: “Plants around the world are actually more productive than we thought.”
The results also mean that while carbon is being taken up by plants faster than previously thought, it is also sequestered for a shorter time. This means that carbon from human activities is being released back into the atmosphere sooner than previously predicted.
Dr Graven added: “Many of the strategies being developed by governments and companies to combat climate change rely on plants and forests to sequester planet-warming CO2.2 and lock it in the ecosystem.
“But our study suggests that the carbon stored in living plants does not stay there as long as we thought. It underscores that the potential for such nature-based carbon removal projects is limited and fossil fuel emissions must be reduced rapidly to minimize the impacts of climate change.”
Use of carbon
Until now, the rate at which plants absorb CO2 to the global production of new tissues and other parts—a measure known as net primary productivity—has been approximated by scaling data from individual sites. However, because there are few sites with comprehensive measurements, it has not been possible to calculate net primary productivity accurately globally.
Plant productivity has increased since the beginning of the 20th century and more CO2 is currently absorbed by plants rather than released back into the air. Researchers know that about 30% of the CO2 Emissions from human activities are therefore stored in plants and soils every year, mitigating climate change and its impacts.
Video summary. Photo credit: Heather Graven / Imperial College London
However, it is not yet known exactly how this storage will be carried out and how stable it will be in the future.
In this study, radiocarbon (14C) – a radioactive carbon isotope – was combined with model simulations to understand how plants use CO2 on a global level and provides valuable insights into the interaction between the atmosphere and the biosphere.
Tracking carbon from bomb tests
Radiocarbon is produced naturally, but atomic bomb tests in the 1950s and 1960s increased the levels of 14C in the atmosphere. This additional 14C was available to plants worldwide, so researchers had a good tool to measure the rate at which they could absorb it.
By examining the accumulation of 14C in power plants between 1963 and 1967 – a time when there were no significant nuclear detonations and the total amount 14C in the Earth system was relatively constant – the authors were able to estimate how quickly carbon from the atmosphere enters the vegetation and what happens to it once it is there.
The results show that currently widely used models simulating how land and vegetation interact with the atmosphere underestimate the net primary productivity of plants worldwide. The results also show that the models overestimate the storage time of carbon in plants.
Role of the biosphere
Co-author Dr. Charles Koven of the Lawrence Berkeley National Laboratory in the US said: “These observations come from a unique moment in history, shortly after the peak of atmospheric nuclear weapons testing in the 1960s.
“The observations show that plant growth at that time was faster than current climate models estimate. The important thing is that this means that the carbon cycle between the atmosphere and the biosphere is faster than we previously thought, and that we need to better understand and account for this faster cycle in climate models.”
According to the authors, the research shows that theories about how plants grow and interact with their ecosystems need to be improved, and global climate models need to be adjusted to better understand how the biosphere mitigates climate change.
Co-author Dr. Will Wieder of the National Center for Atmospheric Research, USA, said: “Scientists and policy makers need better estimates of historical land carbon uptake to make projections of this important ecosystem service for the coming decades. Our study provides important insights into the dynamics of the terrestrial carbon cycle that can serve as the basis for models used for climate projections.”
The work highlights the usefulness of radiocarbon measurements to unravel the complexity of the biosphere. The study’s authors include German physicist Ingeborg Levin, a pioneer of radiocarbon and atmospheric research who sadly passed away in February.
Reference: “Bomb radiocarbon evidence for strong global carbon uptake and turnover in terrestrial vegetation” by Heather D. Graven, Hamish Warren, Holly K. Gibbs, Samar Khatiwala, Charles Koven, Joanna Lester, Ingeborg Levin, Seth A. Spawn-Lee and Will Wieder, 20 June 2024, Science.
DOI: 10.1126/science.adl4443