Earth system response to atmospheric carbon dioxide removal

鉴于国际社会在将温室气体（GHGs）排放量减少到与《巴黎协定》“将全球变暖控制在远低于工业化前水平2摄氏度的水平，并继续努力将温度上升限制在1.5摄氏度以内”的目标一致的水平上的努力拖延，人工从大气中去除二氧化碳的技术建议正受到越来越多的关注。此类二氧化碳去除（CDR）技术包括基于陆地的方法，如重新造林、造林和利用碳捕获和储存（BECCS）生产生物能源、直接从环境空气中捕获二氧化碳的技术、增强海洋碳吸收的方法、增强风化和生物炭。尽管我们对CDR的有效性及其对气候的影响的了解有限，但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1.5°c和2°c一致。

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.