| Summary: | Carbon sequestered as soil inorganic carbon (SIC) provides a regulating ecosystem service, which can be assigned a monetary value based on the avoided social cost of carbon (SC-CO<sub>2</sub>). By definition, the SC-CO<sub>2</sub> is a measure, in dollars, of the long-term damage resulting from the emission of a metric ton of carbon dioxide (CO<sub>2</sub>). Therefore, this dollar figure also represents the value of damages avoided due to an equivalent reduction or sequestration of CO<sub>2</sub>. The objective of this study was to assess the value of SIC stocks in the contiguous United States (U.S.) by soil order, soil depth (0−20, 20−100, 100−200 cm), land resource region (LRR), state, and region using information from the State Soil Geographic (STATSGO) database together with a reported SC-CO<sub>2</sub> of $42 (U.S. dollars). With this approach, the calculated monetary value for total SIC storage in the contiguous U.S. was between $3.48T (i.e., $3.48 trillion U.S. dollars, where T = trillion = 10<sup>12</sup>) and $14.4T, with a midpoint value of $8.34T. Soil orders with the highest (midpoint) values for SIC storage were: 1) Mollisols ($3.57T), 2) Aridisols ($1.99T), and 3) Alfisols ($841B) (i.e., $841B is 841 billion U.S. dollars, where B = billion = 10<sup>9</sup>). When normalized by land area, the soil orders with the highest (midpoint) values for SIC storage were: 1) Vertisols ($3.57 m<sup>−2</sup>), 2) Aridisols ($2.45 m<sup>−2</sup>), and 3) Mollisols ($1.77 m<sup>−2</sup>). Most of the SIC value was associated with the 100−200 cm depth interval, with a midpoint value of $4T and an area-normalized value of $0.54 m<sup>−2</sup>. The LRRs with the highest (midpoint) values of SIC storage were: 1) D—Western Range and Irrigated Region ($1.77T), 2) H—Central Great Plains Winter Wheat and Range Region ($1.49T), and 3) M—Central Feed Grains and Livestock Region ($1.02T). When normalized by land area, the LRRs were ranked: 1) I—Southwest Plateaus and Plains Range and Cotton Region ($5.36 m<sup>−2</sup>), 2) J—Southwestern Prairies Cotton and Forage Region ($4.56 m<sup>−2</sup>), and 3) H—Central Great Plains Winter Wheat and Range Region ($2.56 m<sup>−2</sup>). States with the highest (midpoint) values for SIC storage were: 1) Texas ($2.96T), 2) New Mexico ($572B), and 3) Montana ($524B). When normalized by land area, the states were ranked: 1) Texas ($4.47 m<sup>−2</sup>), 2) Utah ($2.77 m<sup>−2</sup>), and 3) Minnesota ($2.17 m<sup>−2</sup>). Lastly, regions with the highest (midpoint) values for SIC storage were: 1) South Central ($3.13T), 2) West ($1.98T), and 3) Northern Plains ($1.62T). When normalized by land area, the regions were ranked: 1) South Central ($2.90 m<sup>−2</sup>), 2) Midwest ($1.32 m<sup>−2</sup>), and 3) West ($1.02 m<sup>−2</sup>). Results from this study demonstrate a new approach for assigning monetary values to SIC stocks at various scales based on their role in providing ecosystem services for climate regulation and carbon sequestration.
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