Abstract
Abstract. Anthropogenic changes in land use and land cover (LULC) during the pre-industrial Holocene could have affected regional and global climate. Existing scenarios of LULC changes during the Holocene are based on relatively simple assumptions and highly uncertain estimates of population changes through time. Archaeological and palaeoenvironmental reconstructions have the potential to refine these assumptions and estimates. The Past Global Changes (PAGES) LandCover6k initiative is working towards improved reconstructions of LULC globally. In this paper, we document the types of archaeological data that are being collated and how they will be used to improve LULC reconstructions. Given the large methodological uncertainties involved, both in reconstructing LULC from the archaeological data and in implementing these reconstructions into global scenarios of LULC, we propose a protocol to evaluate the revised scenarios using independent pollen-based reconstructions of land cover and climate. Further evaluation of the revised scenarios involves carbon cycle model simulations to determine whether the LULC reconstructions are consistent with constraints provided by ice core records of CO2 evolution and modern-day LULC. Finally, the protocol outlines how the improved LULC reconstructions will be used in palaeoclimate simulations in the Palaeoclimate Modelling Intercomparison Project to quantify the magnitude of anthropogenic impacts on climate through time and ultimately to improve the realism of Holocene climate simulations.
Highlights
Introduction and motivationToday, ca. 10 % of the ice-free land surface is estimated to be intensively managed, and much of the reminder is under less intense anthropogenic use or influenced by human activities (Arneth et al, 2019)
It has been suggested that greenhouse gas emissions associated with Neolithic land use and land cover (LULC) changes were sufficiently large to offset climate cooling after the mid-Holocene
The biogeophysical effects of the accumulated LULC change during the Holocene, which resulted in reconstructed land cover patterns in 1850 CE, have been estimated to cause a slight cooling (0.17 ◦C) that is offset by biogeochemical warming (0.9 ◦C), giving a net global warming (0.73 ◦C) (He et al, 2014)
Summary
Ca. 10 % of the ice-free land surface is estimated to be intensively managed, and much of the reminder is under less intense anthropogenic use or influenced by human activities (Arneth et al, 2019). It has been suggested that greenhouse gas emissions associated with Neolithic LULC changes were sufficiently large to offset climate cooling after the mid-Holocene (the overdue glaciation hypothesis: Ruddiman, 2003) This has been challenged for several reasons, including inconsistency with the land carbon balance derived from ice core and peat records The biogeophysical effects of the accumulated LULC change during the Holocene, which resulted in reconstructed land cover patterns in 1850 CE, have been estimated to cause a slight cooling (0.17 ◦C) that is offset by biogeochemical warming (0.9 ◦C), giving a net global warming (0.73 ◦C) (He et al, 2014) In these simulations, biophysical and biogeochemical effects were of comparable magnitude in the most intensively altered landscapes of Europe, Asia, and North America (He et al, 2014). We present a protocol for implementing LULC in Earth system model simulations to be carried out in the cur-
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