PNNL

Abstract

The long-term temperature goal of the Paris Agreement implies a small and quickly depleting remaining 23 CO2 budget, and the need for fast reductions in non-CO2 greenhouse gas emissions. Despite faster than expected progress in clean energy technology deployment, global annual CO2 emissions have increased for at least two consecutive years after the 2020 COVID shock. The feasibility of limiting warming to 1.5°C is therefore increasingly questioned. We here present a model-intercomparison study that accounts for emissions trends until 2023 and compares cost-effective scenarios with alternative scenarios with institutional, geophysical and technological feasibility constraints and enablers informed by previous literature. Our results show that the most ambitious mitigation trajectories with updated climate information and data still manage to limit peak warming to below 1.6°C (“low overshoot”) with around 60% likelihood. Accounting for feasibility constraints, especially in the institutional dimension (measured through government effectiveness to implement policies), however decreases this maximum likelihood considerably to 10-50%. Additional interventions for accelerated transformation of energy demand can reduce economic costs for reaching staying below 2°C, but have only a limited impact on further increasing the likelihood of limiting warming to 1.6°C. Our study helps to establish a new benchmark of mitigation scenarios that goes beyond the so far dominant cost-effective scenario design.