New Study Shows Inaccuracy in Estimates of the Carbon Cycle Used for Forecasting Climate Change

Scientists from Virginia Tech, in partnership with Pacific Northwest National Laboratory, have revealed that key components of the global carbon cycle used to monitor the movement of carbon dioxide (CO2) in the atmosphere are not accurate, which could considerably change traditional carbon cycle models.

New Study Shows Inaccuracy in Estimates of the Carbon Cycle Used for Forecasting Climate Change.
“We are not challenging the well-established climate change science, but we should be able to account for all carbon in the ecosystem and currently cannot. What we found is that the models of the ecosystem’s response to climate change need updating," said Meredith Steele. Image Credit: Logan Wallace for Virginia Tech.

The approximation of the quantity of CO2 that plants draw from the air is critical to precisely track and estimate the number of climate-changing gasses in the air. This finding will likely alter the estimates for climate change, though it is vague at this moment if the disparity will give rise to more or less CO2 being accounted for in the atmosphere.

Either the amount of carbon coming out of the atmosphere from the plants is wrong or the amount coming out of the soil is wrong.

Meredith Steele, Assistant Professor, School of Plant and Environmental Sciences, College of Agriculture and Life Sciences, Virginia Tech

Meredith Steele’s Ph.D. student at the time, Jinshi Jian, led the study. The findings have been reported in Nature Communications.

We are not challenging the well-established climate change science, but we should be able to account for all carbon in the ecosystem and currently cannot. What we found is that the models of the ecosystem’s response to climate change need updating.

Meredith Steele, Assistant Professor, School of Plant and Environmental Sciences, College of Agriculture and Life Sciences, Virginia Tech

Jian and Steele’s research concentrates on carbon cycling and how soil and plants remove and return CO2 to the air.

To comprehend how carbon impacts the Earth’s ecosystems, it is crucial to be aware of exactly where all the carbon is headed. This process, known as carbon accounting, says how much carbon is transported where, and how much of it is in each of Earth's carbon pools of the oceans, land, atmosphere and living things.

For several years, scientists have been attempting to precisely track where the carbon in the atmosphere is and where it is headed. Virginia Tech and Pacific Northwest National Laboratory scientists concentrated on the CO2 that gets absorbed from the air by plants through photosynthesis.

When animals consume plants, the carbon enters the terrestrial ecosystem. It then is shifted into the soil or to animals. In addition, a large quantity of carbon is also exhaled — or respirated — back into the air.

This CO2 that is coming in and going out is vital for balancing the amount of carbon in the air, which adds to climate change and trapping carbon long-term.

However, the Virginia Tech scientists found that when applying the accepted numbers for soil respiration, that number in the carbon cycling models is no longer well-adjusted.

Photosynthesis and respiration are the driving forces of the carbon cycle, however the total annual sum of each of these at the global scale has been elusive to measure. The authors’ attempts to reconcile these global estimates from different communities show us that they are not entirely self-consistent and there is more to learn about these fundamental processes on the planet.

Lisa Welp, Associate Professor of Earth, Atmospheric, and Planetary Sciences, Purdue University

Lisa Welp is acquainted with the study but was not part of it.

Steele and Jian discovered together with the rest of the team that by using the gross primary productivity of the accepted number of 120 petagrams of CO— each petagram is a billion metric tons — the quantity of carbon coming out via soil respiration must be about 65 petagrams.

By examining many fluxes, the quantity of carbon swapped between Earth's carbon pools of the oceans, land, atmosphere and living things, the researchers discovered that the quantity of carbon soil respiration emitted by the soil was around 95 petagrams.

The gross primary productivity should be about 147. For scale, the variance between the presently established amount of 120 petagrams and this estimate is around three times the global fossil fuel emissions annually.

According to the scientists, there are two likelihoods for this. The first is that the remote sensing method could be underestimating gross primary production. The other likelihood is the upscaling of soil respiration measurements, which could be overestimating the quantity of carbon returned to the air.

Whether this misestimate is a negative or positive thing for the scientifically established challenge of climate change is what has to be analyzed next, Steele stated.

The subsequent step of the study is to establish which part of the global carbon cycling model is being overestimated or underestimated.

By being aware of accurate carbon accounting and where it is in the environment, better models and predictions will be feasible to accurately review the ecosystems’ response to climate change, stated Jian, who started this study as a Ph.D. student at Virginia Tech and is currently at Northwest A&F University in China.

If we think back to how the world was when we were young, the climate has changed. We have more extreme weather events. This study should improve the models we used for carbon cycling and provide better predictions of what the climate will look like in the future.

Jinshi Jian, Study Lead, Northwest A&F University, China

As Steele’s first Ph.D. student at Virginia Tech, a quota of Steele’s startup fund went to aid Jian’s graduate research. Jian, captivated with databases, data science and soil respiration, was involved in another portion of his dissertation when he inadvertently came across something that did not match up.

Jian was exploring how to capture small, localized carbon measurements from across the world. While exploring this, Jian learned that the best estimates did not add up if all the fluxes of global carbon accounting were placed together.

The study received funding from Steele’s startup fund from the College of Agriculture and Life Sciences at Virginia Tech and was additionally supported by the Pacific Northwest National Laboratory.

Journal Reference:

Jian, J., et al. (2022) Historically inconsistent productivity and respiration fluxes in the global terrestrial carbon cycle. Nature Communications. doi.org/10.1038/s41467-022-29391-5.

Source: https://vt.edu

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