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Soils are the largest terrestrial carbon reservoir (2,500 Billion Tons C)
Soils of the world (known in academic parlance as the "pedosphere" or "the soil mantle of the Earth") are the largest reservoir of terrestrial carbon (on the surface of the earth, not to be confused with "fossil carbon" deep underground - i.e. coal, oil, natural gas, etc.). They therefore play an essential role in climate regulation by both sequestering and releasing carbon from and to the atmosphere through natural processes.
According to esteemed soil science scholar, Dr. Rattan Lal of Ohio State University, "Soils of the world constitute the largest reservoir of terrestrial carbon (C) stocks. They comprise both soil organic carbon (SOC) and soil inorganic carbon (SIC), and are an important component of the global C cycle. Estimated to 1 m depth, terrestrial soil (2500 PgC; 1 PgC = petagram of carbon = 1 billion metric tons of carbon) and vegetation (620 PgC) hold three times more C than that in the atmosphere (880 PgC)." (Lal 2021. See featured publication below).
Soils of the world are the largest "terrestrial pool" of carbon, holding approximately 2,500 teratons (teraton = million megatons) of carbon. Even small increases in soil carbon can have a major impact on atmospheric concentrations. Lal 2021
Even small improvements is soil organic matter (SOM) - which is made up of mostly of carbon - can help retain the soil retain significant additional quantities of water, mitigating against both droughts and floods. NRDC 2015
98% of human food is derived from soil, yet soil organic carbon, which impacts nutritional values, has decreased alarmingly around the planet. With global population estimated to increase 30% to 10 billion by 2050, improving soil quality will a cornerstone of food security. Jayaraman 2021, Cerri 2021
Soil4Climate works with regenerative pastoralists and agroecologists in East Africa to restore their native grasslands, and to plant seeds and trees.
1% annual increase in soil carbon stocks would offset annual fossil fuel emissions. According to the International Union for Conservation of Nature (IUCN):
A 0.4% annual increase in soil carbon stocks could nearly offset yearly atmospheric increases in CO2. According to the French initiative, 4p1000, an increase of just 0.4% (4 parts per 1000) of soil carbon would nearly offset the annual increase of atmospheric carbon (4.3 billion tons in 2015). This is based on a calculation of 860 billion tons (gigaton) of carbon in the top 30 to 40 centimeters of soil. An increase in soil carbon can be achieved with regenerative agriculture processes, including "no till" cropping and "pasture management with adapted grazing periods and rotations." 4p1000 Discover
Sustainable Sequestration of Carbon in Soils Increase Food & Climate Security "... intensive use of the soils to meet the growing demand for food, fiber, and energy has caused soil C losses and, consequently, the emissions of greenhouse gases (GHG). For this reason, sustainable soil C sequestration practices and well-oriented political agendas need to be scaled up to regional and national levels to contribute to climate change mitigation and food security" (emphasis added). (Cerri, Carlos Eduardo & Cherubin, Maurício & Damian, Júnior & Mello, Francisco & Lal, Rattan. (2021).
So how do we increase carbon in the soil? According to a fact sheet by American University:
Dr. Rattan Lal, 2021
Karl Thidemann, co-founder and co-director of Soil4Climate, identifies how soil restoration can serve as a vital carbon sink to help stabilize the climate. Karl discusses climate change, photosynthesis, land degradation, and how perennial plants best store carbon in the soil.
Michael Pollen narrates this great explainer video. It covers how healthy soil can be a major carbon sink -- one that absorbs carbon from the atmosphere through photosynthesis. We still need to reduce our fossil fuel emissions, but we don't need to develop expensive or risky technologies. We need to restore soil and plant life!
Dr. David C. Johnson
Mitigating climate change requires clean energy and the removal of atmospheric carbon. Building soil carbon is an appealing way to increase carbon sinks and reduce emissions owing to the associated benefits to agriculture. However, the practical implementation of soil carbon climate strategies lags behind the potential, partly because we lack clarity around the magnitude of opportunity and how to capitalize on it. Here we quantify the role of soil carbon in natural (land-based) climate solutions and review some of the project design mechanisms available to tap into the potential. We show that soil carbon represents 25% of the potential of natural climate solutions (total potential, 23.8 Gt of CO2-equivalent per year), of which 40% is protection of existing soil carbon and 60% is rebuilding depleted stocks. Soil carbon comprises 9% of the mitigation potential of forests, 72% for wetlands and 47% for agriculture and grasslands. Soil carbon is important to land-based efforts to prevent carbon emis- sions, remove atmospheric carbon dioxide and deliver ecosystem services in addition to climate mitigation.
Bossio, D.A., Cook-Patton, S.C., Ellis, P.W. et al. The role of soil carbon in natural climate solutions. Nat Sustain 3, 391–398 (2020). https://doi.org/10.1038/s41893-020-0491-z
Adoption of judicious land use and science-based management practices can lead to re-carbonization of depleted soils and make them a sink for atmospheric C.
Abstract: The soil carbon (C) stock, comprising soil organic C (SOC) and soil inorganic C (SIC) and being the largest reservoir of the terrestrial biosphere, is a critical part of the global C cycle. Soil has been a source of greenhouse gases (GHGs) since the dawn of settled agriculture about 10 millenia ago. Soils of agricultural ecosystems are depleted of their SOC stocks and the magnitude of depletion is greater in those prone to accelerated erosion by water and wind and other degradation processes. Adoption of judicious land use and science-based management practices can lead to re-carbonization of depleted soils and make them a sink for atmospheric C. Soils in humid climates have potential to increase storage of SOC and those in arid and semiarid climates have potential to store both SOC and SIC. Payments to land managers for sequestration of C in soil, based on credible measurement of changes in soil C stocks at farm or landscape levels, are also important for promoting adoption of recommended land use and management practices. In conjunction with a rapid and aggressive reduction in GHG emissions across all sectors of the economy, sequestration of C in soil (and vegetation) can be an important negative emissions method for limiting global warming to 1.5 or 2°C.
Lal R, Monger C, Nave L, Smith P.. The role of soil in regulation of climate, Philosophical Transactions of the Royal Society B: Biological Sciences, 2021 Sep 27 doi: 10.1098/rstb.2021.0084. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8349633/
Lal 2021, Fig 1.
Managing soils for negative feedback to climate change and positive impact on food and nutritional security
Abstract: The increase in atmospheric concentration of carbon dioxide from 278 ppm in the pre-industrial era to 405 ppm in 2018, along with the enrichment of other greenhouse gases, has already caused a global mean temperature increase of 1°C. Among anthropogenic sources, historic land use and conversion of natural to agricultural eco-systems has and continues to be an importance source. Global depletion of soil organic carbon stock by historic land use and soil degradation is estimated at 133 Pg C. Estimated to 2-m depth, C stock is 2047 Pg for soil organic carbon and 1558 Pg for soil inorganic carbon, with a total of 3605 Pg. Thus, even a small change in soil organic carbon stock can have a strong impact on atmospheric CO2concentration. Soil C sink capacity, between 2020 and 2100, with the global adoption of best management practice which creates a positive soil/ecosystem C budget, is estimated at 178 Pg C for soil, 155 Pg C for biomass, and 333 Pg C for the terrestrial biosphere with a total CO2drawdown potential of 157 ppm. Important among techniques of soil organic C sequestration are adoption of a system-based conservation agriculture, agroforestry, biochar, and integration of crops with trees and livestock. There is growing interest among policymakers and the private sector regarding the importance of soil C sequestration for adaptation and mitigation of climate change, harnessing of numerous co-benefits, and strengthening of ecosystem services.
Rattan Lal (2020) Managing soils for negative feedback to climate change and positive impact on food and nutritional security, Soil Science and Plant Nutrition, 66:1, 1-9, DOI: 10.1080/00380768.2020.1718548
Soil carbon storage is a vital ecosystem service, resulting from interactions of ecological processes. Human activities affecting these processes can lead to carbon loss or improved storage.
Abstract: Soils store more carbon than other terrestrial ecosystems1,2. How soil organic carbon (SOC) forms and persists remains uncertain1,3, which makes it challenging to understand how it will respond to climatic change3,4. It has been suggested that soil microorganisms play an important role in SOC formation, preservation and loss5,6,7. Although microorganisms affect the accumulation and loss of soil organic matter through many pathways4,6,8,9,10,11, microbial carbon use efficiency (CUE) is an integrative metric that can capture the balance of these processes12,13. Although CUE has the potential to act as a predictor of variation in SOC storage, the role of CUE in SOC persistence remains unresolved7,14,15. Here we examine the relationship between CUE and the preservation of SOC, and interactions with climate, vegetation and edaphic properties, using a combination of global-scale datasets, a microbial-process explicit model, data assimilation, deep learning and meta-analysis. We find that CUE is at least four times as important as other evaluated factors, such as carbon input, decomposition or vertical transport, in determining SOC storage and its spatial variation across the globe. In addition, CUE shows a positive correlation with SOC content. Our findings point to microbial CUE as a major determinant of global SOC storage. Understanding the microbial processes underlying CUE and their environmental dependence may help the prediction of SOC feedback to a changing climate.
Tao, F., Huang, Y., Hungate, B.A. et al. Microbial carbon use efficiency promotes global soil carbon storage. Nature 618, 981–985 (2023). https://doi.org/10.1038/s41586-023-06042-3
Executive Summary: Soils represent an important carbon (C) pool, being the large sink among the terrestrial ecosystem compartments. However, intensive use of the soils to meet the growing demand for food, fiber and energy has caused soil C losses and consequently, the emissions of greenhouse gases (GHG). For this reason, sustainable soil C sequestration practices and well-oriented political agendas need to be scaled up to regional and national levels to contribute to climate change mitigation and food security. In 2020, the Inter-American Institute for Cooperation on Agriculture (IICA) and the Carbon Management and Sequestration Center at The Ohio State University (CMASC) launched the Living Soils of the Americas (LiSAm) initiative .... we found that pasture is the most widespread agricultural use of land in the Americas, accounting for 9.05km2 x 106 (905 million ha). Pasture surface area is three times larger than that of agriculture (croplands), accounting for 3.40 km2 x 106 . Soybean (0.91 km2 x 106 ), maize (0.72 km2 x 106 ) and wheat (0.35 km2 x 106 ) are the most cultivated annual crops, sugarcane (0.14 km2 x 106 ) is the main semi-perennial crop, and coffee (0.05 km2 x 106 ) is the main perennial crop. For the soil C stocks, we estimated an average accumulation of 51.28 Mg ha-1 in the entire hemisphere for the 0-30 cm layer. Among the different regions, Central America (63.30 Mg ha-1), the Caribbean (61.35 Mg ha-1) and North America (53.91 Mg ha-1) showed the highest soil C stocks ... Based on our estimate, adopting only two large-scale sustainable management practices (i.e., pasture reclamation and conservation tillage) the potential soil C accumulation in the countries of the Americas is about 2.68 Pg C (1.25 – 4.11 Pg C), representing a total of 9.81 Pg.
Cerri, Carlos Eduardo & Cherubin, Maurício & Damian, Júnior & Mello, Francisco & Lal, Rattan. (2021). Soil carbon sequestration through adopting sustainable management practices: potential and opportunity for the American countries. Link
Yongfei Bai M. Francesca Cotrufo, Science 4 Aug 2022
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