Plants release carbon faster than we expected

A recent study has revealed that the global carbon stored by plants is shorter-lived and more susceptible to climate change than previously believed. 

The results indicate that current climate models underestimate the annual global uptake of carbon dioxide (CO2) by vegetation and overestimate the amount of time that this carbon remains stored.

Carbon cycling in plants

The research, led by Dr. Heather Graven at Imperial College London, has significant implications for understanding nature’s role in mitigating climate change, particularly concerning nature-based carbon removal projects like mass tree planting.

“Plants across the world are actually more productive than we thought they were,” noted Dr. Graven. However, while plants absorb carbon faster than expected, they also release it faster. 

This means that carbon from human activities will be released back into the atmosphere sooner than previously predicted, noted the researchers. 

Carbon removal strategies 

“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,” said Dr. Graven. 

“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.”

Net primary productivity 

Until now, the global measure of net primary productivity (NPP) – which represents the rate at which plants use CO2 to create new tissues – has been approximated from limited site-specific data. 

The lack of comprehensive measurements has made it challenging to accurately calculate net primary productivity on a global scale. 

Since the early 1900s, plant productivity has increased, with more CO2 being absorbed by plants than released back into the atmosphere. 

Approximately 30% of human CO2 emissions are stored in plants and soils each year, helping to mitigate climate change. However, the stability and future of this carbon storage remain poorly understood.

Global plant carbon usage 

In this study, radiocarbon (14C), a radioactive isotope of carbon, was used alongside model simulations to study global plant CO2 usage. This approach produced valuable insights into the interaction between the atmosphere and the biosphere. 

Radiocarbon levels increased due to nuclear bomb testing in the 1950s and 1960s, offering researchers a tool to measure plant uptake rates. 

By analyzing 14C accumulation in plants from 1963 to 1967, the experts assessed the carbon transfer from the atmosphere to vegetation and its subsequent fate.

Models overestimate plant carbon storage

The findings reveal that current models underestimate global plant productivity and overestimate carbon storage duration in plants. 

“These observations are from a unique moment in history, just after the peak of atomic weapons testing in the atmosphere in the 1960s,” noted Dr. Charles Koven from Lawrence Berkeley National Laboratory.

“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.”

New insights into carbon cycle dynamics 

The research underscores the need to improve theories about plant growth and ecosystem interactions and adjust global climate models for better understanding of the biosphere’s role in mitigating climate change. 

“Scientists and policymakers need improved estimates of historical land carbon uptake to inform projections of this critical ecosystem service in future decades,” said Dr. Will Wieder from the National Center for Atmospheric Research. 

“Our study provides critical insights into terrestrial carbon cycle dynamics, which can inform models that are used for climate change projections.”

According to the researchers, their work highlights the usefulness of radiocarbon measurements in helping to unravel the complexities of the biosphere.

The study authors included German physicist Ingeborg Levin, a pioneer in radiocarbon and atmospheric research, who passed away in February.

The research is published in the journal Science.

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