Aerosols have a dimming and cooling effect and change hydrological regimes, thus affecting carbon fluxes, which are sensitive to climate. Aerosols also scatter sunlight, which increases the fraction of diffuse radiation, increasing photosynthesis. There remains no clear conclusion whether the impact of aerosols on land carbon fluxes is larger through diffuse radiation change than through changes in other climate variables. In this study, we quantified the overall physical impacts of anthropogenic aerosols on land C fluxes and explored the contribution from each factor using a set of factorial simulations driven by climate and aerosol data from the IPSL-CM6A-LR experiments during 1850–2014. A newly developed land surface model which distinguishes diffuse and direct radiation in canopy radiation transmission, ORCHIDEE_DF, was used. Specifically, a subgrid scheme was developed to distinguish the cloudy and clear sky conditions. We found that anthropogenic aerosol emissions since 1850 cumulatively enhanced the land C sink by 22.6 PgC. Seventy-eight percent of this C sink enhancement is contributed by aerosol-induced increase in the diffuse radiation fraction, much larger than the effect of the aerosol-induced dimming. The cooling of anthropogenic aerosols has different impacts in different latitudes but overall increases the global land C sink. The dominant role of diffuse radiation changes found in this study implies that future aerosol emissions may have a much stronger impacts on the C cycle through changing radiation quality than through changing climate alone. Earth system models need to consider the diffuse radiation fertilization effect to better evaluate the impacts of climate change mitigation scenarios.

中文翻译：

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解开 1850 年至 2014 年期间人为气溶胶对陆地碳循环的影响


气溶胶具有变暗和冷却作用，可以改变水文状况，从而影响对气候敏感的碳通量。气溶胶还会散射阳光，从而增加漫射辐射的比例，从而增强光合作用。目前还没有明确的结论，气溶胶通过扩散辐射变化对陆地碳通量的影响是否比通过其他气候变量的变化更大。在这项研究中，我们量化了人为气溶胶对陆地碳通量的总体物理影响，并使用一组由 1850-2014 年 IPSL-CM6A-LR 实验的气候和气溶胶数据驱动的因子模拟探讨了每个因素的贡献。使用了新开发的陆地表面模型ORCHIDEE_DF，该模型区分冠层辐射传输中的漫射辐射和直接辐射。具体来说，开发了一种子网格方案来区分多云和晴空条件。我们发现，自 1850 年以来，人为气溶胶排放累计使陆地碳汇增加了 22.6 PgC。这种碳汇增强的 78% 是由气溶胶引起的漫射辐射部分的增加贡献的，远大于气溶胶引起的调光的效果。人为气溶胶的冷却在不同纬度有不同的影响，但总体上增加了全球陆地碳汇。本研究中发现的漫射辐射变化的主导作用意味着，未来气溶胶排放可能通过改变辐射质量对碳循环产生比单独改变气候更大的影响。地球系统模型需要考虑漫射辐射施肥效应，以更好地评估气候变化减缓情景的影响。