Future levels of climate change depend not only on carbon emissions but also on carbon uptake by the land and the ocean. Here we are using the Earth system model (ESM1) version of the Australian Community Climate and Earth System Simulator (ACCESS) to explore the potential and impact of removing carbon dioxide (CO₂) from the atmosphere through the climate and carbon cycle reversibility experiment. This experiment builds on the standard Coupled Model Intercomparison Project (CMIP) experiment, increasing CO₂ at 1% per year until 4xCO₂ is reached. The atmospheric CO₂ levels are then decreased at the same rate which brings the CO₂ back to pre-industrial levels. We then continue to run the model with constant CO₂ for another 350 years. Our analysis focuses on the response of the land carbon cycle. We find that carbon stores are largely reversible at the global scale over the timescale of changing CO₂. However, carbon stores continue to decrease after CO₂ returns to its initial value, and the land loses another 40 Pg of carbon (PgC) with the largest change in the tropics. It takes about 300 years beyond the period of changing CO₂ for the carbon stores to recover. Interestingly, we saw strong regional variations in the strength of the land response to changing CO₂. Australia showed the largest increase/decrease in biomass carbon (about 40%) and the largest variability in productivity, which was strongly correlated with rainfall. This highlights the importance of assessing the regional response to understanding the processes underlying the response and the sensitivity of these processes within each model. This understanding will benefit future multi-model analyses of this reversibility experiment. It also illustrates more generally the potential to use Earth system model experiments as part of the evaluation of proposed applications of carbon dioxide removal (CDR) technologies. As such, we recommend that these types of modelling experiments be included when mitigation policies are developed.

中文翻译：

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在澳大利亚社区气候和地球系统模拟器中评估陆地气候和碳可逆性

未来的气候变化水平不仅取决于碳排放量，还取决于陆地和海洋的碳吸收量。在这里，我们使用澳大利亚社区气候和地球系统模拟器（ACCESS）的地球系统模型（ESM1）版本，通过气候和碳循环可逆性实验来探索从大气中去除二氧化碳（CO ₂）的潜力和影响。该实验基于标准的耦合模型比较项目（CMIP）实验，以每年1％的速度增加CO ₂，直到达到4xCO ₂为止。然后以相同的速率降低大气中的CO ₂水平，使CO ₂返回工业化前水平。然后，我们继续以恒定CO运行模型₂持续350年。我们的分析集中在陆地碳循环的响应上。我们发现，在改变CO ₂的时间范围内，碳储量在全球范围内是可逆的。但是，CO ₂恢复到其初始值后，碳储量继续减少，并且该土地又损失了40 Pg的碳（PgC），这在热带地区变化最大。在改变CO ₂的时间之后，要恢复碳存储大约需要300年。有趣的是，我们发现土地对CO ₂变化的反应强度存在很大的区域差异。澳大利亚显示出最大的生物量碳增/减量（约40％）和最大的生产率差异，这与降雨密切相关。这突出了评估区域响应以理解响应背后的过程以及每个模型中这些过程的敏感性的重要性。这种理解将有益于该可逆性实验的未来多模型分析。它还更一般地说明了使用地球系统模型实验作为评估二氧化碳去除（CDR）技术的建议应用的一部分的潜力。因此，我们建议在制定缓解策略时包括这些类型的建模实验。