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Titel Using reconstructions of the global peat C balance over the Holocene to constrain the timing and magnitude of anthropogenic land use emissions
VerfasserIn Benjamin Stocker, Zicheng Yu, Charly Massa, Renato Spahni, Colin Prentice, Fortunat Joos
Konferenz EGU General Assembly 2016
Medientyp Artikel
Sprache en
Digitales Dokument PDF
Erschienen In: GRA - Volume 18 (2016)
Datensatznummer 250135449
Publikation (Nr.) Volltext-Dokument vorhandenEGU/EGU2016-16315.pdf
 
Zusammenfassung
Major circumpolar peatlands of the northern hemisphere have established over the last 14 kyr, with the majority of peat C sequestered during the Holocene. Today, this C storage amounts to 500-600 GtC. In spite of this substantial impact on the C cycle, independent records of the total terrestrial C balance suggest a small long-term trend over the last 6 kyr. The advent of agriculture, associated land use change, and resulting cumulative CO2 emissions of 50-350 GtC have occurred during a period of continued C sequestration in peatlands. Relatively small variations in the total terrestrial C balance have thus been interpreted to indicate a coincidental timing and a similar magnitude of these compensating fluxes and to lend support for upper-end estimates of preindustrial land use emissions. Here, we test this hypothesis by combining observation-based reconstructions of the terrestrial C balance (ΔC) and peat storage (ΔCpeat) with new results from process-based global land C cycle models that hindcast peat C dynamics and CO2 emissions from anthropogenic land use change (ΔCLUC) following a set of contrasting land use reconstructions. Recent data compilations of peat C accumulation histories allow us to provide an improved temporal resolution of observation-based ΔCpeat. We assess the terrestrial C budget ΔC = ΔCpeat+ δ for different periods in the Holocene and in the last millennium and confront ΔCLUC with the budget residual δ. We find that the combination of ΔCpeat and ΔC and their temporal variations provide additional constraints on ΔCLUC estimates that have thus far not been taken into account. Between 11-7 kyr BP, ΔCpeat alone accounts for the majority of ΔC, incompatible with upper-end ΔCLUC estimates. Between 7-5 kyr BP and 5-2 kyr BP, the budget reveals a substantial land C source, but all model-based estimates of ΔCLUC fall short of explaining the magnitude of δ. ΔC reveals a relatively stable overall C balance during the last millennium before 1750, but substantial C loss from land thereafter. The combination of ΔCpeat and ΔC estimates thus support land use reconstructions with negligible ΔCLUC before 7 kyr BP and a substantial fraction of ΔCLUC occurring after Industrialisation.