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 from 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 like large-scale tree planting.
New research indicates 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.
According to a new study, the global carbon stored by plants is more short-lived and susceptible to climate change than previously believed. These findings have significant implications for our understanding of nature’s role in mitigating climate change, particularly for nature-based carbon removal projects like mass tree-planting initiatives.
The research, carried out by an international team led by Dr. Heather Graven at Imperial College London and published in the journal 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, a 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 into 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.
Video abstract. Credit: Heather Graven / Imperial College London
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.
Tracking carbon from bomb tests
Radiocarbon is produced naturally, but nuclear bomb testing in the 1950s and 1960s increased the level of 14C in the atmosphere. This extra 14C was available to plants globally, giving researchers a good tool to measure how fast they could take it up.
By examining the accumulation of 14C in plants between 1963 and 1967 – a period when there were no significant nuclear detonations and the total 14C in the Earth system was relatively constant – the authors could assess how quickly carbon moves from the atmosphere to vegetation and what happens to it once it’s 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. 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, USA, said: “These observations are from a unique moment in history, just after the peak of atomic weapons testing in the atmosphere in the 1960s.
“The observations show that the growth of plants at the time was faster than current climate models estimate that it was. The significance is that it 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 say the research demonstrates the need to improve theories about how plants grow and interact with their ecosystems, and to adjust global climate models accordingly, to better understand how the biosphere is mitigating climate change.
Co-author Dr. Will Wieder, from the National Center for Atmospheric Research, USA, said: “Scientists and policymakers need improved estimates of historical land carbon uptake to inform projections of this critical ecosystem service in future decades. Our study provides critical insights into terrestrial carbon cycle dynamics, which can inform models that are used for climate change projections.”
The work highlights the usefulness of radiocarbon measurements in helping to unpick the complexities of the biosphere. The study’s authors include German physicist Ingeborg Levin, a pioneer in radiocarbon and atmospheric research, who sadly died 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
What if increased CO2 is just a by-product of global warming and not the driving force behind it? Just like it’s a by-product in a glasshouse. Then all this cultural mayhem and economic catastrophy over green policies will have been for nothing.
One wonders why there should be cultural mayhem and economic catastrophe about changing our sources of energy, changing the type of cars we drive and simply using less energy, as we used to do in say 1950?
What’s the problem, unless one is making big profits from selling oil and gas and ooal and demanding subsidies from the taxpayer (government) to do so?
Was there cultural mayhem when we progressed from feudalism to the steam age? I suppose that the USA’s Indian population didn’t enjoy the change as the white man built those railways across the USA……….