Earth system response to atmospheric carbon dioxide removal

鉴于国际社会迟迟未能努力将温室气体排放量减少到符合巴黎目标的水平，即将全球变暖限制在“远低于工业化前水平2摄氏度的水平，并努力将温度上升限制在1.5摄氏度以下”，因此，关于从大气中人工去除二氧化碳的技术的建议正受到越来越多的关注。这种二氧化碳清除技术包括重新造林、植树造林和利用碳捕获和储存的生物能源生产等陆基方法、直接从环境空气中捕获二氧化碳的技术、提高海洋碳吸收的方法、增强风化作用和生物炭。CDR是温室气体排放情景的一个组成部分，与将升温限制在工业化前的1.5C和2C以上相一致，尽管我们对CDR的有效性及其对气候的影响了解有限。** 拟议的研究旨在通过追求以下目标来填补这一知识空白：* 推进我们对CDR对耦合气候-碳循环系统的影响的理解，并量化CDR作为CO2减排措施的有效性。确定我们关于气候碳循环对正CO2排放的响应的知识在多大程度上适用于CDR响应。*探索在涉及暂时超过变暖目标的情景下人类引起的气候变化的可逆性。这些目标将使用地球系统模型来实现，这些模型是复杂的数字模型，代表地球系统的不同组成部分（例如大气层、海洋、陆地表面、生物圈）及其相互作用。更好地理解气候和碳循环对《气候变化框架公约》的反应是制定有效气候政策的关键，这些政策使加拿大和国际社会走上了实现巴黎气候目标的轨道。例如，大多数与将升温限制在远低于2摄氏度相一致的情景假设，目前温室气体减排的延迟可以通过未来大规模部署CDR来补偿。如果事实证明CDR的效果不如假设的那么好，或者在暂时超过变暖目标后气候影响是不可逆转的，那么这种情景可能是不可行的。

Given the delay in international efforts to reduce emissions of greenhouse gases (GHGs) to a level consistent with the Paris goal of limiting global warming “to well below 2C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5C”, proposals for technologies to artificially remove CO2 from the atmosphere are receiving increasing attention. Such carbon dioxide removal (CDR) technologies include land-based methods such as reforestation, afforestation and bio-energy production with carbon capture and storage (BECCS), technologies that capture CO2 directly from ambient air, methods to enhance ocean carbon uptake, enhanced weathering and biochar. CDR is an integral part of GHG emission scenarios consistent with limiting warming to 1.5C and 2C above pre-industrial, although we have only limited knowledge of the effectiveness of CDR and its effects on climate. ******The proposed research seeks to fill this knowledge gap by pursuing the following objectives:*** Advance our understanding of the effects of CDR on the coupled climate-carbon cycle system and quantify the effectiveness of CDR as a CO2 mitigation measure.*** Establish the extent to which our knowledge of the response of coupled-climate carbon cycle to positive CO2 emissions is applicable to the response to CDR.*** Explore the reversibility of human-induced climate changes under scenarios that involve a temporary overshoot of the warming goal.******These objectives will be addressed using Earth System Models, which are complex numerical models hat represent the different Earth System components (e.g. atmosphere, ocean, land surface, biosphere) and the interactions among them. A better understanding of the climate and carbon cycle response to CDR is key to designing effective climate policies that put Canada and the international community on track to meeting the Paris climate goals. Most scenarios that are consistent with limiting warming to well below 2C, for instance, assume that current delays in GHG emission reductions can be compensated by large-scale deployment of CDR in the future. If it turns out that CDR is less effective than assumed, or climate impacts are irreversible following a temporary overshoot of the warming target, such scenarios may not be viable.