Abstract
Abstract. Land-use change has been the dominant source of anthropogenic carbon emissions for most of the historical period and is currently one of the largest and most uncertain components of the global carbon cycle. Advancing the scientific understanding on this topic requires that the best data be used as input to state-of-the-art models in well-organized scientific assessments. The Land-Use Harmonization 2 dataset (LUH2), previously developed and used as input for simulations of the 6th Coupled Model Intercomparison Project (CMIP6), has been updated annually to provide required input to land models in the annual Global Carbon Budget (GCB) assessments. Here we discuss the methodology for producing these annual LUH2-GCB updates and extensions which incorporate annual wood harvest data updates from the Food and Agriculture Organization (FAO) of the United Nations for dataset years after 2015 and the History Database of the Global Environment (HYDE) gridded cropland and grazing area data updates (based on annual FAO cropland and grazing area data updates) for dataset years after 2012, along with extrapolations to the current year due to a lag of 1 or more years in the FAO data releases. The resulting updated LUH2-GCB datasets have provided global, annual gridded land-use and land-use-change data relating to agricultural expansion, deforestation, wood harvesting, shifting cultivation, regrowth and afforestation, crop rotations, and pasture management and are used by both bookkeeping models and dynamic global vegetation models (DGVMs) for the GCB. For GCB 2019, a more significant update to LUH2 was produced, LUH2-GCB2019 (https://doi.org/10.3334/ORNLDAAC/1851, Chini et al., 2020b), to take advantage of new data inputs that corrected cropland and grazing areas in the globally important region of Brazil as far back as 1950. From 1951 to 2012 the LUH2-GCB2019 dataset begins to diverge from the version of LUH2 used for the World Climate Research Programme's CMIP6, with peak differences in Brazil in the year 2000 for grazing land (difference of 100 000 km2) and in the year 2009 for cropland (difference of 77 000 km2), along with significant sub-national reorganization of agricultural land-use patterns within Brazil. The LUH2-GCB2019 dataset provides the base for future LUH2-GCB updates, including the recent LUH2-GCB2020 dataset, and presents a starting point for operationalizing the creation of these datasets to reduce time lags due to the multiple input dataset and model latencies.
Highlights
Human-induced changes to the Earth’s carbon cycle are known to have driven changes in the Earth’s climate system with far-reaching consequences for all components of the Earth system including the atmosphere, oceans, land, and human society
Global grazing land area increased from 26.1 × 106 km2 in 1950, peaked in the year 2000 at 33.2×106 km2 or peaked in 2001 at 33.1×106 km2, and decreased to 32.8 × 106 km2 in 2015 or 32.7 × 106 km2 in 2015 and 32.6 × 106 km2 in 2019
The Land-Use Harmonization 2 dataset (LUH2)-GCB2019 dataset (Chini et al, 2020b) is the annual update to the LUH2 dataset for use as input to the ensemble of international dynamic global vegetation models (DGVMs) (TRENDY DGVM model synthesis; Sitch et al, 2015) that delivers to the Global Carbon Budget 2019. It was based on existing LUH2 methodology (Hurtt et al, 2020) with updated inputs from History Database of the Global Environment (HYDE) and from Food and Agriculture Organization (FAO)
Summary
Human-induced changes to the Earth’s carbon cycle are known to have driven changes in the Earth’s climate system with far-reaching consequences for all components of the Earth system including the atmosphere, oceans, land, and human society. To gain improved understanding of the anthropogenic disturbances of the global carbon cycle and provide decision support for climate policies, the Global Carbon Project has coordinated the publication of an annual carbon budget since 2005 (Le Quéré et al, 2014; Friedlingstein et al, 2019). From 1750 to 2018, land-usechange emissions total 235 ± 75 Pg C and fossil fuel emissions total 440 ± 20 Pg C, with annual fossil fuel emissions surpassing land-use-change emissions in the mid-20th century (Friedlingstein et al, 2019) They are no longer the dominant source of human-generated carbon emissions, contemporary land-use emissions remain a large and highly uncertain term in the global carbon budget and a driver of the interannual variability in the land carbon balance (Yue et al, 2020). Landuse-related carbon emissions and removal are likely to become increasingly important in the future with both increasing demand for food and fiber by a growing and more affluent population and the potential adoption of climate mitigation strategies that heavily involve the terrestrial biosphere (such as biofuel crop production, afforestation and forest restoration, and more sustainable agricultural management practices, some of which target the C budget) (Popp et al, 2017)
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