Fair distributions of carbon dioxide removal obligations and implications for effective national net-zero targets

Achieving net-zero emissions at the global level, as required to limit warming to 1.5 °C, means both rapid emissions reductions across all sectors as well as a scaling-up of carbon dioxide removal (CDR). As a growing number of countries bring forward national net-zero targets, the questions of how much CDR each nation holds responsibility for, whether CDR transfers should be possible under the Paris Agreement market mechanisms, and how this might affect the years in which different countries should achieve net-zero, become increasingly important. Here we show that, depending on the normative assumptions underlying a CDR burden-sharing system, the adjusted net-zero date for big emitting countries could shift forward by up to 15 years (EU, based on gross domestic product) to 35 years (Russia, based on cumulative per capita emissions) compared with what is modeled domestically in global least-cost scenarios. This illustrates a challenge of using least-cost model scenarios as a basis for setting and evaluating net-zero targets. We also evaluate the potential risk of carbon loss associated with CDR transfers of such a magnitude, and consider how a discount factor could help address carbon loss risks and contribute to overall mitigation. Our results highlight the need for clear guidelines to ensure that international CDR transfers do not obscure urgently-needed domestic emission reductions efforts by big emitters, while promoting a fair and equitable distribution of the CDR burden inflicted by insufficient near-term mitigation. We find a separate mechanism or accounting for CDR obligations to be the most promising avenue to deliver on these objectives.