Remote carbon cycle changes are overlooked impacts of land-cover and land management changes

Le résumé fourni par la source

Abstract. Land-cover and land management changes (LCLMCs) have a substantial impact on the global carbon budget and, consequently, global climate. However, LCLMCs also influence climate by altering the surface energy balance, namely biogeophysical (BGP) effects. BGP effects act locally, but also nonlocally through advection or atmospheric circulation changes. Previous studies have shown potentially substantial nonlocal BGP effects on temperature and precipitation. Given that the terrestrial carbon cycle strongly depends on climate conditions, this raises the question of whether LCLMCs can trigger remote carbon cycle changes – a currently overlooked potentially large climate and ecosystem impact. To assess these nonlocal biogeochemical (BGC) effects, we analyze sensitivity simulations for three selected types of hypothetical large-scale LCLMCs: global cropland expansion, global cropland expansion with irrigation, and global afforestation, which were performed by three state-of-the-art Earth system models. We separate the nonlocal BGC effect using a checkerboard-like LCLMC perturbation that has previously only been applied to BGP effects. We show that nonlocal BGC effects on vegetation and soil carbon pools persistently accumulate, exceeding natural fluctuations and typically becoming detectable within the first 40 years after LCLMCs. By the end of our 160-year simulation period, the global total terrestrial carbon stock differs by 1 to 37 GtC, with strong changes over the densely forested Amazon region (0.2 to 7 GtC) and Congo region (0.3 to 15 GtC), depending on models and scenarios. For the irrigation scenario, the nonlocal BGC effects are comparable to the total BGC effects. Our results reveal that the nonlocal BGC effects could be substantial and call for these effects to be considered for accurate impact assessment and sound policymaking. This becomes even more relevant when LCLMCs are expected to play a pivotal role in achieving the Paris Agreement’s goal of limiting global warming below 1.5 °C above pre-industrial levels.

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