Manan Bhan , Patrick Meyfroidt, Sarah Matej, Karl-Heinz Erb, Simone Gingrich

Biomass carbon stocks (BCS) play a vital role in the climate system, but benchmarked estimates prior to the late 20th century remain scarce. Here, by making use of an early global forest resource assessment and harmonizing information on land use and carbon densities, we establish a global BCS account for the year 1950. Our best-guess BCS estimate is 450.7 PgC (median of all modulations: 518.3 PgC, range: 443.9-584.6 PgC), with ecosystems in Southern America and Western Africa storing c. 27 and 16% of the total respectively. Our estimates are in line with land change emissions estimates and suggest a reduction in BCS of 8-29% compared to the median, with losses in tropical subcontinents partially offset by gains in northern subcontinents. Our study demonstrates an approach to reconstruct global BCS over the 20th century to complement carbon flux-based modelling efforts and identify emerging global land transitions.