The Net Radiative Forcing from Ozone-Depleting Substances and its Uncertainty

Key Points 

• The net radiative forcing from ozone-depleting substances is uncertain but there is a high probability of a warming impact  

• Simple models can be used to separate the contributors to net radiative impacts for each ozone-depleting substance  

• CFC-12 has by far the largest net radiative forcing of ozone-depleting substances

Abstract 

The effective radiative forcing of long-lived ozone-depleting substances is large, around 15-20% of CO2. Their net effective radiative forcing, which considers the wider chemical feedbacks in the atmosphere, is less well understood. Here, we use a simple climate model, which has been adapted to consider the radiative feedbacks from ozone-depleting substances, to quantify this uncertainty. We find that the effective radiative forcing of ozone-depleting substances in 2019 of 0.35 (0.31, 0.39) W m−2 reduces to a net radiative forcing of 0.11 (-0.02, 0.26) mW m−2, considering feedbacks. We use this simple model to quantify the net effective radiative forcing of each individual ozone-depleting substance and feedback. Most of the net radiative forcing from ozone-depleting substances is from CFC-12 and HCFCs, while others have mitigated the warming impact. This results in an increase in the net radiative forcing from ozone-depleting substances in 2019 compared to when the Montreal Protocol was implemented in 1987.  

Plain Language Summary

Ozone-depleting substances, such as chlorofluorocarbons (CFCs), damage the ozone layer and also contribute to climate change by trapping heat. Their direct warming effect is quite well understood. However, their total impact on climate, including additional feedbacks such as changes to the chemistry of the atmosphere, is less certain. In this study, we used a simple climate model to account for these feedbacks. We found that the total warming impact of ozone-depleting substances in 2019 is much smaller than their direct effect. Our model helps identify how much each substance contributes, which is difficult in larger climate models. We find that most of the warming comes from one, CFC-12, with much of the additional warming coming from hydrochlorofluorocarbons, which are one class of replacement gases for CFCs and cause less damage to the ozone layer. Our results highlight the need for further research to better understand these climate effects.