Society's material stocks as carbon pool: an economy-wide quantification of global carbon stocks from 1900-2015

Societal activities massively alter the global carbon (C) cycle, thereby driving global climate heating. Socioeconomic material stocks - e.g. in buildings and infrastructures - have been identified as a C pool that can potentially store increasing amounts of C, thereby keeping C away from the atmosphere. However, little is known about the size, composition, distribution and development of global socioeconomic C stocks. Based on an established economy-wide C accounting approach from sociometabolic research, we consistently and comprehensively quantified the C contained in eight components of socioeconomic stocks in the period 1900-2015 at the level of nine world regions. We discern inert (aggregates and other gravel) and 'active' climate-relevant (i.e. biomass and fossil-fuel based) C pools. We find that global active components of socioeconomic C stocks grew by a factor of 9, from 1.9 (1.5-2.2) Pg of carbon (PgC) to 16.8 (13.7-20.2) PgC. The inert socioeconomic C stock in aggregates & other gravel amounted to 25.2 (6.1-48.0) PgC in 2015, however with high uncertainties. Absolute annual net additions to stock (NAS) of active stock components was 0.49 (0.40-0.59) PgC yr-1 which equaled 5% of the C emissions from fossil fuel combustion and industrial processes. However, raising NAS of components with biomass feedstock that sequester C from the atmosphere comes with biodiversity and food security trade-offs. This study contributes to a holistic perspective on social and natural C stocks that acknowledges their interactions. The global socioeconomic C stock reached a geologically relevant extent (approximately the size of C in coasts) and should therefore be integrated in the assessments of the global C cycle to acknowledge the Anthropocene.