Earth system response to atmospheric carbon dioxide removal

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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 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5°C”, 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 1.5°C and 2°C 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 2°C, 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.