Net zero emissions of greenhouse gases by 2050: achievable and at what cost?

About 140 countries have announced or are considering net zero targets. To explore the implications of such targets, we apply an integrated earth system-economic model to investigate illustrative net zero emissions scenarios. Given the technologies as characterized in our modeling framework, we find that with net zero targets afforestation in earlier years and biomass energy with carbon capture and storage (BECCS) technology in later years are important negative emissions technologies, allowing continued emissions from hard-to-reduce sectors and sources. With the entire world achieving net zero by 2050 a very rapid scale-up of BECCS is required, increasing mitigation costs through mid-century substantially, compared with a scenario where some countries achieve net zero by 2050 while others continue some emissions in the latter half of the century. The scenarios slightly overshoot 1.5(& LCIRC;)C at mid-century but are at or below 1.5(& LCIRC;)C by 2100 with median climate response. Accounting for climate uncertainty, global achievement of net zero by 2050 essentially guarantees that the 1.5(& LCIRC;)C target will be achieved, compared to having a 50-50 chance in the scenario without net zero. This indicates a tradeoff between policy costs and likelihood of achieving 1.5(& LCIRC;)C.