Since biochar degrades over time, any claim about the volume of total carbon removal facilitated by biochar should be accompanied by a clear claim about the associated time horizon of storage. The degradation of biochar applied to soils is contingent on the physical and chemical characteristics of biochar (see Biomass transformation) and the environment in which it is applied. Simple models relating biochar elemental ratios or volatile matter content to its stability may provide some indication of expected longevity of carbon storage, and by extension, the mass of carbon remaining in biochar over a specified time horizon. However, these models do not extrapolate with confidence over long time horizons or capture variability critical environmental factors that drive degradation like climate, temperature, moisture, soil type and texture, and microbial and fungal communities. Estimates of carbon lost from biochar should also take into account the potential for biochar’s environment to change through time, for example by eroding off of agricultural fields or migrating through the soil column. Better characterizing biochar degradation is an active area of research. Note that although this component specifically focuses on biochar applied to soils, biochar could be stored (e.g. buried at depth) or productized (e.g. embedded in concrete) in a way that constrains degradation uncertainty.