To what extent can carbon losses from the soil to the atmosphere accelerate climate change?

Soil microorganisms break down organic matter and release carbon dioxide (CO2) into the atmosphere through heterotrophic respiration. An increase in the activity of these microorganisms, something that can be caused by global warming, releases carbon from the soil, which contributes to increasing the concentration of atmospheric CO2.

An international study, led by the Spanish Higher Council for Scientific Research (CSIC), shows great losses of soil organic carbon through microbial decomposition caused by anthropogenic warming. The work indicates that the arctic and sub-arctic regions are the ones that store the most carbon in the soil. These areas, in turn, are warming at a rate roughly twice the world average, potentially leading to high net losses of soil carbon globally.

“There is more carbon in the biosphere than in the atmosphere. In fact, the largest reserve of biologically active carbon in terrestrial ecosystems is found in the first two meters of soil, where more than 2,200-2,500 petagram (Pg) of carbon are stored. For this reason, the losses, even if they are small, can contribute to increasing the concentrations of CO2 in the atmosphere, which stores 750 Pg of carbon and, therefore, accelerate climate change ”, explains Pablo García-Palacios, scientist at the CSIC in the Institute of Agrarian Sciences (ICA-CSIC).

The authors have analyzed different climate databases and soil carbon density on a global scale. “Although there is no consensus on the magnitude of the loss of soil carbon with anthropogenic warming, there are two strong evidences that suggest important losses at a global level: the increase in soil respiration with rising temperatures and the accumulation of carbon from the soil in cold regions ”, points out García-Palacios. “Until now, the size of the carbon pool was balanced annually between carbon losses from soil respiration and gains from carbon fixation by plants. However, anthropogenic warming is upsetting this balance ”, he adds.

Low temperatures are the main responsible for the accumulation of organic carbon in the soil. (Photo: César Hernández / CSIC Comunicación)

Human activities are estimated to have caused global warming of about 1.0 ° C relative to pre-industrial levels. The Paris Agreement, signed by 195 states, set the objective of preventing the increase in the global average temperature of the planet from exceeding 2 ° C, and promotes additional efforts so that it does not exceed 1.5 ° C. “If we take into account that low temperatures are the main responsible for the accumulation of carbon in the soil, it seems highly probable that anthropogenic warming at higher latitudes will cause large net losses globally. The authorities must take this reality into account since our study indicates that, to meet the objective of the Intergovernmental Group of Experts on Climate Change (IPCC) of not exceeding 1.5 ° C by 2100, it is necessary to commit to making reductions in the most ambitious greenhouse gas emissions ”, concludes the scientist.

In the work, which proposes to continue studying the microbial community-temperature interactions to improve the estimates of climate change, researchers from the Rey Juan Carlos University and the University of Alicante, both in Spain, have also participated.

The study is published under the title “Evidence for large microbial-mediated losses of soil carbon under anthropogenic warming” in the academic journal Nature Reviews Earth & Environment. (Source: CSIC)

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