The Net Effective Radiative Forcing From Ozone‐Depleting Substances and Its Uncertainty

The direct effective radiative forcing (ERF) of long‐lived ozone‐depleting substances (ODS) is around 15%–20% of the pre‐industrial to present‐day ERF of , but their net ERF, including indirect chemical adjustments, remains poorly constrained. We use an adapted simple climate model, trained on bulk indirect ODS forcing from complex climate models, to quantify uncertainty in net ERF over time and the net ERF across individual ODS. We find that the direct ODS ERF in 2019 of 0.35 (0.31, 0.39) W is reduced to a net ERF of 0.11 (−0.02, 0.26) W when chemical adjustments are included. Most net ERF arises from CFC‐12 and HCFC‐22 (0.18 W ), with chemical adjustments substantially reducing the net ERF of many other substances. Since the implementation of the Montreal Protocol, the total ODS net ERF has increased much less rapidly than the direct ERF.