Session: Benchmarking & cross-cutting Group 1 (Isotope modelling, COMPARE)
Author: Benjamin Stocker / email@example.com / CREAF, Barcelona, Spain
Co-author: Zicheng Yu, Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, USA;
Charly Massa, Department of Geography, Universiy of Hawaii at Manoa, Honolulu, USA;
Fortunat Joos, Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland;
CO2 emissions from preindustrial land-use change (LUC) are subject to large uncertainties. Although atmospheric CO2 records suggest only a small land carbon (C) source since 5,000 y before present (5 kyBP), the concurrent C sink by peat buildup could mask large early LUC emissions. Here, we combine updated continuous peat C reconstructions with the land C balance inferred from double deconvolution analyses of atmospheric CO2 and δ13C at different temporal scales to investigate the terrestrial C budget of the Holocene and the last millennium and constrain LUC emissions. LUC emissions are estimated with transient model simu- lations for diverging published scenarios of LU area change and shifting cultivation. Our results reveal a large terrestrial nonpeat- land C source after the Mid-Holocene (66 ± 25 PgC at 7–5 kyBP and 115 ± 27 PgC at 5–3 kyBP). Despite high simulated per-capita CO2 emissions from LUC in early phases of agricultural development, humans emerge as a driver with dominant global C cycle impacts only in the most recent three millennia. Sole anthropogenic causes for particular variations in the CO2 record (∼20 ppm rise after 7 kyBP and ∼10 ppm fall between 1500 CE and 1600 CE) are not supported. This analysis puts a strong constraint on preindustrial vs. industrial-era LUC emissions and suggests that upper-end scenarios for the extent of agricultural expansion before 1850 CE are not compatible with the C budget thereafter.