A recent study has found that plants store carbon for shorter durations and are more vulnerable to climate change than previously believed. This discovery impacts our understanding of nature’s role in mitigating climate change, including the effectiveness of projects like mass tree-planting.
Conducted by an international team led by Dr. Heather Graven from Imperial College London, the research was published in the journal Science. It shows that current climate models underestimate the amount of carbon dioxide (CO2) absorbed by vegetation each year and overestimate how long that carbon remains stored.
Dr. Graven, a Reader in Climate Physics at Imperial’s Department of Physics, stated, “Plants across the world are actually more productive than we thought they were.” However, while plants absorb carbon more quickly, they also release it back into the atmosphere sooner than expected.
This finding challenges many current climate strategies that depend on plants and forests to sequester CO2. Dr. Graven emphasized the need for a rapid reduction in fossil fuel emissions, noting, “Our study suggests that carbon stored in living plants does not stay there as long as we thought.”
Understanding Plant Carbon Use
Historically, the rate at which plants use CO2 to grow—a measure known as Net Primary Productivity—has been estimated by scaling up data from specific sites. Due to the limited number of comprehensive measurement sites, accurately calculating global Net Primary Productivity has been challenging.
Since the early 1900s, plant productivity has increased, with plants absorbing more CO2 than they release. It is known that about 30% of human CO2 emissions are stored in plants and soils each year, helping to mitigate climate change. However, the processes and stability of this carbon storage are not fully understood.
Using Radiocarbon to Track Carbon Dynamics
The study used radiocarbon (14C), a radioactive carbon isotope, alongside model simulations to understand global CO2 use by plants. The 1950s and 1960s nuclear bomb tests increased atmospheric 14C levels, providing researchers a means to measure plant carbon uptake.
By examining 14C accumulation in plants between 1963 and 1967, the researchers assessed how quickly carbon moves from the atmosphere to vegetation. The results indicated that current models underestimate plant productivity and overestimate carbon storage duration.
Implications for Climate Models
Co-author Dr. Charles Koven from the Lawrence Berkeley National Laboratory highlighted the significance of these observations. “The growth of plants during the 1960s was faster than current climate models estimate. This implies that carbon cycles more rapidly between the atmosphere and biosphere than previously thought,” he said.
The study calls for improved theories on plant growth and interactions within ecosystems to refine global climate models and better understand the biosphere’s role in mitigating climate change.
Dr. Will Wieder from the National Center for Atmospheric Research added, “Our study provides critical insights into terrestrial carbon cycle dynamics, informing models used for climate change projections.”
The research underscores the value of radiocarbon measurements in understanding the complexities of the biosphere. The study’s authors include Ingeborg Levin, a German physicist and pioneer in radiocarbon and atmospheric research, who passed away in February.