Climate Engineering on Land: Comprehensive evaluation of Earth system impacts of terrestrial carbon dioxide removal (CE-LAND+)

陆地二氧化碳去除（tCDR）方法，包括植树造林和专门的生物质种植园，有时被称为有效、“绿色”和安全的气候工程（CE）选择，因为它们增加了生物圈作为二氧化碳汇的自然功能，并且在经济上似乎是可行的。然而，来自CE- land项目第一阶段的证据表明，tCDR与其他CE选择一样具有争议，因为它指出了困难的地球系统和伦理考虑。因此，除了二氧化碳预算和对tCDR方法的经济考虑之外，还需要对它们的环境限制、它们对地球系统的影响以及相关的不确定性、它们与其他土地和水利用的权衡以及它们可能产生的深远的伦理影响进行合理的分析。对项目第一阶段假设情景的分析表明，要使tCDR有效，需要大量土地面积，因此将出现与其他土地用途的艰难权衡。此外，结果表明，除了预期的全球平均温度降低外，还会对气候系统和陆地生物地球化学循环产生显著的副作用。CE-LAND+将对tCDR生物圈转型的非经济成本进行更深入、定量和空间明确的评估。它将通过采用两种生物地球物理植被模型、一种地球系统模型和项目新引入的动态生物多样性模型，解决潜在的权衡和影响，并对其估计中的主要不确定性进行系统分析。具体而言，CE-LAND+将调查迄今为止大部分未量化的权衡，一方面是最大限度地扩大tCDR面积和生物多样性保护之间的权衡，另一方面是最大限度地扩大tCDR淡水供应与粮食生产和河流生态系统之间的权衡。此外，还将量化背景气候变化和与tdr相关的土地利用变化对水资源短缺（基于不同的指标，也假设不同的灌溉管理水平）和生物多样性的直接影响。除了减少气候变化之外，还将考虑全球可持续发展目标，即生物多样性保护、淡水安全和粮食安全，这些都是优先计划中没有提供的背景。此外，该项目将通过研究模型结构差异、高温、高二氧化碳条件下tCDR植物的生长和死亡率，以及tCDR土地利用活动与气候之间的反馈，有助于更好地理解和量化未来气候变化下tCDR效应的关键不确定性。最后，CE-LAND+将在优先项目的合作下，与我们的一组具有代表性的情景一起，从环境伦理的角度评估与tdr相关的权衡。

Terrestrial Carbon Dioxide Removal (tCDR) methods, comprising afforestation and dedicated biomass plantations, are sometimes referred to as effective, 'green' and safe climate engineering (CE) options, as they increase the biosphere's natural function as a CO2 sink and appear to be economically feasible. However, evidence from the first phase of the CE-LAND project indicates that tCDR is as controversial as other CE options as it points to difficult Earth-systemic and ethical considerations. Mere CO2 budgeting and economic consideration of tCDR methods thus needs to be supplemented by sound analysis of their environmental limits, their impacts on the Earth system with related uncertainties, their tradeoffs with other land and water uses, and their potentially far-reaching ethical implications. Analysis of hypothetical scenarios in the first project phase suggests that substantial land areas would be required for tCDR to be effective, such that tough tradeoffs with other land uses would emerge. Moreover, results indicate that significant side-effects on the climate system (besides the intended reduction of global mean temperature) and on terrestrial biogeochemical cycles would occur. CE-LAND+ will deliver a more in-depth, quantitative and spatially explicit evaluation of non-economic costs of biosphere transformation for tCDR. It will address potential tradeoffs and impacts along with a systematic analysis of major uncertainties in their estimation by employing two biogeophysical vegetation models, one Earth system model and, new to the project, dynamic biodiversity models. Specifically, CE-LAND+ will investigate the - hitherto largely unquantified - tradeoffs between maximising areas for tCDR and biodiversity protection on the one hand, and between maximising freshwater availability for tCDR and both food production and river ecosystems on the other hand, respectively. Also, the (in)direct impacts of background climate change and tCDR-related land use change on water scarcity (based on different metrics, also assuming different levels of irrigation management) and biodiversity will be quantified. The tradeoffs and impacts will be contextualised with a view on global sustainability goals besides abating climate change, namely biodiversity conservation, freshwater security and food security - a context otherwise not provided in the Priority Program. Furthermore, the project will contribute to a better understanding and quantification of key uncertainties of tCDR effects under future climate change by examining model-structural differences, growth and mortality of tCDR plants under high-temperature, high-CO2 conditions, and feedbacks between tCDR land use activities and climate. Finally, CE-LAND+ will contribute, in cooperations within the Priority Program and with a representative set of our scenarios, to the evaluation of tCDR-related tradeoffs from an environmental ethics perspective.