carbon flux estimates are imprecise and blur predictions

[EN VIDÉO] Global carbon dioxide 2020-2021 Visualization of data showing volumetric carbon dioxide on a global scale for the period from June 1, 2020 to July 31, 2021.

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General
Symbol: CNatomic number: 6Electrons per energy level: 2.4Atomic mass: 12.011 uMost stable isotopes: 12C stable with six…” data-image=”https://cdn.futura-sciences.com/buildsv6/ images/midioriginal/2/1/9/2198868bcb_69707_carbone.jpg” data-url=”https://www.futura-sciences.com/sciences/definitions/chimie-carbone-3873/” data-more=”Read more “>carbone is exchanged on Earth between the four large tanks natural that areatmospherethe biospherethe hydrosphere and the lithosphere and is dynamically renewed thanks to the pedosphere (the soils) which is at the interface of these large reservoirs. This journey of carbon by biogeochemical exchange is the carbon cycle, and the quantification of its flux is important for future climate prediction models.

The dominant carbon fluxes are gross primary productivity (mass of carbon assimilated by plants via the photosynthesis) and respiration (rejection of CO₂ by plants, especially the soil). Although significant progress has been made in measuring them, such as using models established by satellite remote sensing and measures in situ (i.e. with measuring devices) at the ecosystem scale, they still remain a major source of uncertainty.

Difficult to accurately estimate carbon fluxes

A team of researchers led by Jinshi Jian published a study in Nature Communications showing that there are large discrepancies between published estimates of gross primary productivity and respiration. Indeed, these two phenomena are vital in the carbon cycle but the total annual sum on a global scale is difficult to measure. In seeking to reconcile these global estimates, Virginia Tech researchers, in collaboration with the Pacific Northwest National Laboratoryfound that they were not all consistent.

This discovery is essential because these estimates are used in models of future climate projections; and if they are inaccurate (or incorrect), the models come out inaccurate too. At this stage, it is impossible to know if this will play in favor of a greater or lesser quantity of CO₂ in the environment, but it is obvious that this bias does not call into question the well-established science of anthropogenic climate change which occurs. Nevertheless, the amount of gas present in the atmosphere modifies the climate, therefore the estimate of the quantity of CO₂ released by plants is essential to predict the evolution of the future climate.

More precise measurements to generate better climate predictions

To make projections of the future climate, it is important to understand and be able to follow the exact path of carbon. How much carbon goes where? How much is in each tank? Jinshi Jian and his colleagues have therefore studied the way in which vegetation – plant and soil – eliminates and restores the CO₂ in the air.

The currently accepted amount of gross primary productivity is about 113 petagrams of CO₂ (1 petagram equals 1 billion tonnes), and the amount of carbon released through respiration should be around 65 petagrams. But, by analyzing the different flows of carbon exchanged between the large reservoirs, the researchers discovered a quantity of carbon leaving the soil of around 95 petagrams, and a gross primary productivity of around 149 petagrams. These differences correspond to about three times theepisode annual world fuels fossils, which is not at all negligible.

These discrepancies could come either from an underestimation of gross primary production by the use of remote sensing, or from an overestimation of respiration when this is scaling world. The next goal will therefore be to determine which part is underestimated or overestimated in global carbon cycle models, in order to refine their accuracy and generate better climate predictions.