Managing Overshoot Through Collective Carbon Debt Drawdown

Managing Overshoot Through Collective Carbon Debt Drawdown

Setu Pelz, Oliver Fricko, Keywan Riahi, Shonali Pachauri, Elina Brutschin, Joeri Rogelj, Volker Krey, Injy Johnstone, Adriano Vinca, Carl F. Schleussner, Jarmo Kikstra, Matthew J. Gidden

The impending breach of the 1.5C limit requires urgent collective action to minimize overshoot magnitude. To date, most Integrated Assessment Model (IAM) experiments treat the principles and norms informing collective action as distinct and typically ex-post considerations, separating, for example, assessments of fairness from the scenario modelling process. Here, we propose and demonstrate a modular framework that endogenizes fairness considerations directly into standard IAM scenario generation processes. We use ‘carbon debt’ to track and minimise regional responsibilities for overshoot corresponding to varied considerations of fairness, and thereby identify a broader solution space for collective high-ambition than previously recognized. We demonstrate that high-responsibility regions can manage this carbon debt through varying combinations of interregional financial transfers and intensified near-term domestic gross emissions reductions. Pathways prioritizing domestic gross reductions lower interregional financial transfer obligations and reduce the reliance on novel carbon dioxide removal in lower-responsibility regions. Conversely, delaying the onset of cooperation increases global energy system investment costs. Ultimately, our results indicate that considerations of fairness are wholly consistent with collective global 1.5°C pathways and can provide a wider solution space informing multilateral deliberations.