Estimates of the carbon cycle – vital to predicting climate change – are incorrect, Virginia Tech researchers show – Watts Up With That?

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The findings don’t contradict established climate change science, but they do highlight how accounting for the amount of carbon taken out by plants and returned by the soil is not accurate.

Peer-reviewed publication


Researchers at Virginia Tech, in collaboration with the Pacific Northwest National Laboratory, found that key parts of the global carbon cycle used to track the movement of carbon dioxide in the environment are not correct, which could significantly alter conventional models of the carbon cycle.

Estimating how much carbon dioxide plants remove from the atmosphere is critical to accurately monitoring and predicting the amount of climate-changing gases in the atmosphere. This finding has the potential to change predictions of climate change, although at this time it is unclear whether the mismatch will result in more or less carbon dioxide in the environment.

“Either the amount of carbon leaving the atmosphere from plants is wrong, or the amount leaving the soil is wrong,” said Meredith Steele, an assistant professor in the College of Plant and Environmental Sciences in the College of Agriculture and Life. Sciences, whose Ph.D. student at the time, Jinshi Jian, led the investigation team. The findings will be published on Friday in nature communications.

“We’re not challenging well-established climate change science, but we should be able to account for all the carbon in the ecosystem and we currently can’t,” he said. “What we found is that the models of the ecosystem response to climate change need to be updated.”

Jian and Steele’s work focuses on the carbon cycle and how plants and soil remove and return carbon dioxide to the atmosphere.

To understand how carbon affects Earth’s ecosystems, it’s important to know exactly where all the carbon goes. This process, called carbon accounting, tells how much carbon goes where, how much is in each of the Earth’s carbon pools in the oceans, atmosphere, land, and living things.

For decades, researchers have been trying to get an accurate accounting of where our carbon is and where it’s going. Researchers from Virginia Tech and Pacific Northwest National Laboratory focused on the carbon dioxide that plants extract from the atmosphere through photosynthesis.

When animals eat plants, the carbon is moved into the terrestrial ecosystem. Then it passes to the ground or to animals. And a lot of carbon is also exhaled, or breathed in, back into the atmosphere.

This carbon dioxide going in and out is essential to balance the amount of carbon in the atmosphere, which contributes to climate change and long-term carbon storage.

However, the Virginia Tech researchers found that when the accepted numbers for soil respiration are used, that number in carbon cycle models is no longer balanced.

“Photosynthesis and respiration are the driving forces of the carbon cycle, yet the annual sum total of each of these on a global scale has been difficult to measure,” said Lisa Welp, associate professor of earth, atmospheric and planetary sciences. at Purdue. University, who is familiar with the work but was not part of the investigation. “The authors’ attempts to reconcile these global estimates from different communities show us that they are not entirely consistent with each other and that there is more to learn about these fundamental processes on the planet.”

What Jian and Steele, along with the rest of the team, found is that by using the gross primary productivity of the accepted number of 120 petagrams of carbon dioxide (each petagram is one billion metric tons), the amount of carbon leaving through soil respiration should be in the neighborhood of 65 petagrams.

By looking at multiple fluxes, the amount of carbon exchanged between Earth’s carbon stores in the oceans, atmosphere, land, and living things, the researchers found that the soil respiration amount of carbon leaving the soil is approximately 95 petagrams. Gross primary productivity should be around 147. For scale, the difference between the currently accepted amount of 120 petagrams and this estimate is about three times global fossil fuel emissions each year.

According to the researchers, there are two possibilities for this. The first is that the remote sensing approach may be underestimating gross primary production. The other is expanding measurements of soil respiration, which could be overestimating the amount of carbon returned to the atmosphere. Whether this erroneous estimate is a positive or negative for the scientifically proven challenge of climate change is what needs to be examined next, Steele said.

The next step in the investigation is to determine which part of the global model of the carbon cycle is being underestimated or overestimated.

By having an accurate accounting of carbon and where it is in the ecosystem, better predictions and models will be possible to accurately judge the response of these ecosystems to climate change, said Jian, who began this research as a Ph.D. student at Virginia Tech and is now at Northwest A&F University in China.

“If we remember what the world was like when we were young, the climate has changed,” Jian said. “We have more extreme weather events. This study should improve the models we use for the carbon cycle and provide better predictions of what the climate will be like in the future.”

As the first Ph.D. of Steele. student at Virginia Tech, a portion of Steele’s seed fund went to support Jian’s graduate research. Jian, fascinated with data science, databases, and ground breathing, was working on another part of his dissertation when he stumbled upon something that didn’t quite add up.

Jian was investigating how to take small, localized carbon measurements around the world. While investigating this, Jian discovered that the best estimates did not match up if all the flows from the global carbon accounting were put together.

The research was funded by Steele’s seed fund from the College of Agriculture and Life Sciences at Virginia Tech and with additional support from the Pacific Northwest National Laboratory.


nature communications




Does not apply


Historically inconsistent flows of productivity and respiration in the global terrestrial carbon cycle



From Eurek Alert!


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