Uncertainties in the land-use flux resulting from land-use change reconstructions and gross land transitions

• Published in: Earth system dynamics 2017-02, Vol.8 (1), p.91-111
• Main Authors: Bayer, Anita D, Lindeskog, Mats, Pugh, Thomas A. M, Anthoni, Peter M, Fuchs, Richard, Arneth, Almut
• Format: Article
• Language: English
• Subjects: Abandonment; Agricultural land; Analysis; Atmospheric models; Biogeochemistry; Carbon; Carbon emissions; Climate change; Climate change mitigation; Climate Research; Complexity; Computer simulation; Cover crops; Cultivation; Datasets; Earth and Related Environmental Sciences; Ecosystem models; Ecosystems; Emissions; Emissions (Pollution); Environment models; Fluxes; Geovetenskap och miljövetenskap; Global temperature changes; Grasslands; Harvest; Klimatforskning; Laboratorium voor Geo-informatiekunde en remote sensing; Laboratory of Geo-information Science and Remote Sensing; Land cover; Land use; Land use controls; Mitigation; Natural Sciences; Natural vegetation; Naturvetenskap; Pasture; PE&RC; Plant cover; Pollution control; Reconstruction; Representations; Shifting cultivation; Soil; Soils; State-of-the-art reviews; Stocks; Tropical climate; Tropical environment; Tropical environments; Uncertainty; Uncertainty analysis; Vegetation; Vegetation cover
• ISSN: 2190-4987; 2190-4979; 2190-4987
• DOI: 10.5194/esd-8-91-2017

Land-use and land-cover (LUC) changes are a key uncertainty when attributing changes in measured atmospheric CO2 concentration to its sinks and sources and must also be much better understood to determine the possibilities for land-based climate change mitigation, especially in the light of human demand on other land-based resources. On the spatial scale typically used in terrestrial ecosystem models (0.5 or 1°) changes in LUC over time periods of a few years or more can include bidirectional changes on the sub-grid level, such as the parallel expansion and abandonment of agricultural land (e.g. in shifting cultivation) or cropland–grassland conversion (and vice versa). These complex changes between classes within a grid cell have often been neglected in previous studies, and only net changes of land between natural vegetation cover, cropland and pastures accounted for, mainly because of a lack of reliable high-resolution historical information on gross land transitions, in combination with technical limitations within the models themselves. In the present study we applied a state-of-the-art dynamic global vegetation model with a detailed representation of croplands and carbon–nitrogen dynamics to quantify the uncertainty in terrestrial ecosystem carbon stocks and fluxes arising from the choice between net and gross representations of LUC. We used three frequently applied global, one recent global and one recent European LUC datasets, two of which resolve gross land transitions, either in Europe or in certain tropical regions. When considering only net changes, land-use-transition uncertainties (expressed as 1 standard deviation around decadal means of four models) in global carbon emissions from LUC (ELUC) are ±0.19, ±0.66 and ±0.47 Pg C a−1 in the 1980s, 1990s and 2000s, respectively, or between 14 and 39 % of mean ELUC. Carbon stocks at the end of the 20th century vary by ±11 Pg C for vegetation and ±37 Pg C for soil C due to the choice of LUC reconstruction, i.e. around 3 % of the respective C pools. Accounting for sub-grid (gross) land conversions significantly increased the effect of LUC on global and European carbon stocks and fluxes, most noticeably enhancing global cumulative ELUC by 33 Pg C (1750–2014) and entailing a significant reduction in carbon stored in vegetation, although the effect on soil C stocks was limited. Simulations demonstrated that assessments of historical carbon stocks and fluxes are highly uncertain due to the choice of LUC r