A new study reveals that the carbon stored by plants worldwide is more volatile and vulnerable to the effects of climate change than previously thought. The research, led by Dr. Heather Graven, from Imperial College London, shows that current climate models significantly underestimate how much CO2 is absorbed by vegetation each year and overestimate its duration, suggesting that carbon is being released back into the atmosphere sooner than expected. This points to a 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 plantings.
New research shows that plants absorb and release carbon dioxide faster than previously thought, calling into question the effectiveness of nature-based carbon removal strategies and underscoring the urgency to reduce fossil fuel emissions to fight climate change.
Global carbon storage by plants is shorter-lived and more sensitive to climate change than previously thought, according to a new study. These findings have significant implications for our understanding of nature’s role in climate change mitigation, particularly for nature-based carbon removal projects such as mass tree planting initiatives.
The research, conducted by an international team led by Dr Heather Graven at Imperial College London and published in Scienceshows that existing climate models increase the amount of carbon dioxide (CO2) that is absorbed by vegetation worldwide every year, while how long that carbon stays there is overestimated.
Dr. Graven, a reader in climate physics in Imperial’s physics department, said: “Plants around the world are actually more productive than we thought.”
The findings also mean that while carbon is taken up by plants more quickly than thought, the carbon is also retained for a shorter time, meaning that 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 companies to tackle climate change rely on plants and forests to reduce warming CO2 emissions.2 and lock it up in the ecosystem.
“But our research shows that the carbon stored in living plants doesn’t stay there as long as we thought. It highlights that the potential for such nature-based carbon removal projects is limited, and fossil fuel emissions must be rapidly reduced to minimize the impact of climate change.”
The use of carbon
So far, the rate at which plants use CO22 to produce new fabrics and other parts globally – a metric known as Net Primary Productivity – has been approached by scaling up data from individual sites. But the scarcity of sites with comprehensive measurements means it has not been possible to accurately calculate net primary productivity worldwide.
Plant productivity has increased since the early 20th century and more CO2 has been created2 is currently absorbed by plants and then released back into the air. Researchers know that about 30% of CO2 Emissions from human activities are therefore stored in plants and soils every year, reducing climate change and its impacts.
Video summary. Credit: Heather Graven / Imperial College London
However, the details of how this storage occurs and its stability in 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 on a global scale, unlocking valuable insights into the interaction between the atmosphere and the biosphere.
Tracking carbon from bomb tests
Radiocarbon is produced naturally, but nuclear bomb testing in the 1950s and 1960s increased the level of the radiocarbon. 14C in the atmosphere. This extra 14C was available to plants worldwide, giving researchers a good tool to measure how quickly they could absorb it.
By examining the accumulation of 14C in power stations between 1963 and 1967 – a period when there were no significant nuclear explosions and the total 14C in the Earth system was relatively constant – the authors were able to assess how quickly carbon moves from the atmosphere to vegetation and what happens to it once it gets 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 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, from Lawrence Berkeley National Laboratory, US, said: “These observations date from a unique moment in history, just after the peak of nuclear weapons testing in the atmosphere in the 1960s.
“The observations show that plant growth at the time was faster than estimated by current climate models. The significance is that this implies that the carbon cycles between the atmosphere and the biosphere are happening faster than we thought, and that we need to better understand these faster cycles and take them into account in climate models.”
The authors say the research shows the need to improve theories of how plants grow and interact with their ecosystems, and to adjust global climate models accordingly, to better understand how the biosphere mitigates climate change.
Co-author Dr. Will Wieder, from the National Center for Atmospheric Research, US, said: “Scientists and policymakers need better estimates of historical carbon uptake by land to make predictions about this crucial ecosystem service in the coming decades. Our study provides critical insights into the dynamics of the terrestrial carbon cycle, which can inform models used for climate change projections.”
The work highlights the usefulness of radiocarbon measurements in helping to unravel the complexity of the biosphere. The study’s authors include German physicist Ingeborg Levin, a pioneer in radiocarbon and atmospheric research, who sadly passed away in February.
Reference: “Bomb Radiocarbon Evidence for Strong Global Carbon Capture 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 Wil Wieder, June 20, 2024, Science.
DOI: 10.1126/science.adl4443