Crowther et al.1 reported that the best predictor of surface soil carbon (top 10 cm) losses in response to warming is the size of the surface carbon stock in the soil (that is, carbon stocks in plots that have not been warmed), finding that soils that are high in soil carbon also lose more carbon under warming conditions. This relationship was based on a linear regression of soil carbon losses and soil carbon stocks in field warming studies, which was then used to project carbon losses over time and to generate a map of soil carbon vulnerability. However, a few extreme
data points (high-leverage points) can strongly influence the slope of a regression line2. Only 5 of the 49 sites analysed by Crowther et al.1 are in the upper half of the carbon stock range, which raises the possibility that the relationship they observed could be substantially altered by introducing data from sites with relatively high surface soil carbon stocks. There is a Reply to this Comment by Crowther, T. W. et al. Nature 554, http://dx.doi.org/10.1038/nature25746 (2018). We obtained information on soil carbon losses from 94 additional
field warming studies worldwide and added these published and unpublished data to the dataset used by Crowther et al.1, thereby tripling this previous dataset to a total of 143 studies (Supplementary Table 1). We performed the same mixed-model regression analyses as were used by Crowther et al.1 to investigate spatial patterns of soil
carbon responses to warming, by linking these to standing soil carbon stocks, climate data and soil properties (see Supplementary Methods for details, Supplementary Table 2 for study-specific data regarding soil properties and climate, and Supplementary Table 3 for Akaike information criterion results).
