3.1 Pg C/year: 3% of current global ecosystem respiration: ~30% of current anthropogenic emissions
||Hicks Pries CE, Castanha C, Porras RC, Torn MS. The whole-soil carbon flux in response to warming. Science. 2017 Mar 31355(6332):1420-1423. doi: 10.1126/science.aal1319. P.1422 middle columnPubMed ID28280251
|| B. Bond-Lamberty, A. Thomson, Temperature-associated increases in the global soil respiration record. Nature 464, 579–582 (2010). doi:10.1038/nature08930  C. Le Quéré et al., Global carbon budget 2016. Earth Syst. Sci. Data 8, 605–649 (2016). doi:10.5194/essd-8-605-2016PubMed ID20336143
||P.1420 right column 2nd paragraph: "[Investigators] warmed soils 4° ± 0.75°C from 10 cm down to 100 cm in the soil profile in three pairs of control and heated plots from November 2013 through February 2016 (Fig. 1 and figs. S1 and S2). [They] used 22 heating rods, each 2.4 m deep, arranged around plots 3 m in diameter (ref 17) with two additional circular heating cables buried 5 cm below the soil surface at radii of 0.5 and 1 m from the plot center. This method imposed 4°C warming while preserving the natural depth gradient and temporal variations in soil temperature. At 5 cm, because of the lack of aboveground heating, the heated plots were on average only 2.4° ± 1.2°C warmer than the control. Soil moisture was slightly decreased in the warmed plots by an average of 1.5 to 3.5% volumetric water content (fig. S3). The soil respiration response, which included microbial and root respiration (but see supplementary text), was determined monthly from seven replicate surface flux measurements per plot and by measuring gas well CO2 concentrations at five depths (15, 30, 50, 70, and 90 cm), from which depth-resolved CO2 production estimates were modeled using Fick’s law."
||P.1422 middle column: "As a preliminary test of global significance, extrapolating the subsoil response to all mineral soil orders (leaving out cryosols, histosols, and moisture-limited aridisols) on a C stock basis [1091 Pg (ref 15)], subsoils could lose 3.1 Pg C year^−1 as a result of 4°C warming. This estimate assumes that all mineral soils have similar microbial accessibility and depth distributions of SOC [soil organic carbon] and is based on [investigators’] soil’s initial response, which may be transient (ref 31). However, this potentially large subsoil response to warming should not be ignored. The response would be roughly 3% of current global ecosystem respiration (primary source 32) and roughly 30% of current anthropogenic emissions (primary source 33). Because previous warming experiments have missed the response of deeper soils to warming, and because terrestrial models often have a low Q10, the strength of the SOC-climate feedback may be currently underestimated." Pg=Peta gram=10^15 grams