Assessing tipping-point risk in carbon dioxide removal with a network-based framework

Abstract

Carbon dioxide removal (CDR) strategies are central to long-term plans for reaching carbon neutrality, and projections of their mitigation potential underpin national and global carbon accounting. How reliably a strategy delivers that potential depends on how its technology interacts with the natural carbon cycle, and in particular on whether the coupled system can settle into more than one steady state. Throughout, a tipping point means an abrupt transition from one positive steady state of the coupled system to a different one. Multiple steady states are a necessary condition for such a transition since a system with only one has no second state to move to. Such a shift would leave the strategy removing far less CO₂ than projected, invalidating the carbon accounting that justified it, and recovery may be slow. Using Chemical Reaction Network Theory (CRNT), we represent four CDR strategies (biochar sequestration, ocean fertilization, soil carbon sequestration, and wetland restoration) as networks of carbon pools and the transfers between them. From the graphical and kinetic structure of each network alone, without exact rate values, we identify the conditions under which multiple steady states can exist and those under which they are excluded. For ocean fertilization, multiple steady states are guaranteed in one regime of the natural carbon cycle, provided the technology's own reaction sensitivities also meet additional conditions; outside this identified regime, the framework does not rule multistationarity out. Biochar sequestration and soil carbon sequestration share the broadest reach across the regimes in which multiple steady states can occur, reflecting shared features of their networks. Wetland restoration departs most from the others, admitting at most one steady state in a regime where the other three admit multiple. The network-level structure of a CDR system is therefore itself an assessment criterion for the reliability of projected carbon removal, and CRNT offers a parameter-minimal first screen for tipping-point risk, complementing conceptual and numerical carbon-cycle models.

Keywords

Carbon dioxide removal / multiple steady states / tipping points / carbon cycle / chemical reaction network theory / carbon neutrality / CDR risk assessment / earth system models

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