title: Holocene peatland and ice-core data constraints on the timing and magnitude of CO2emissions from past land use.
abstract: CO2emissions from preindustrial land-use change (LUC) are subject to large uncertainties. Although atmospheric CO2records 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 CO2and [Formula: see text]C 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 simulations for diverging published scenarios of LU area change and shifting cultivation. Our results reveal a large terrestrial nonpeatland C source after the Mid-Holocene (66 [Formula: see text] 25 PgC at 7-5 kyBP and 115 [Formula: see text] 27 PgC at 5-3 kyBP). Despite high simulated per-capita CO2emissions 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 CO2record ([Formula: see text]20 ppm rise after 7 kyBP and [Formula: see text]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.
authors.affiliation: Life Science Department, Imperial College London, Silwood Park, Ascot, Berkshire SL5 7PY, United Kingdom; beni.stocker@env.ethz.ch.|Institute for Atmospheric and Climate Science, Eidgenössische Technische Hochschule Zürich, 8092 Zurich, Switzerland.|Climate and Environmental Physics, Physics Institute, University of Bern, 3012 Bern, Switzerland.
authors.forename: Benjamin David
authors.identifier: 0000-0003-2697-9096
authors.initials: BD
authors.lastname: Stocker
authors.affiliation: Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, PA 18015.
authors.forename: Zicheng
authors.identifier: 0000-0003-2358-2712
authors.initials: Z
authors.lastname: Yu
authors.affiliation: Department of Geography, Universiy of Hawaii at Mānoa, Honolulu, HI 96822.
authors.forename: Charly
authors.initials: C
authors.lastname: Massa
authors.affiliation: Climate and Environmental Physics, Physics Institute, University of Bern, 3012 Bern, Switzerland.|Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland.
authors.forename: Fortunat
authors.identifier: 0000-0002-9483-6030
authors.initials: F
authors.lastname: Joos
keywords: Anthropocene; agriculture; carbon cycle; ice core; peatland