Large Contribution of Ozone‐Depleting Substances to Global and Arctic Warming in the Late 20th Century

While previous studies have suggested a substantial role of ozone-depleting substances (ODSs) in historical climate change, their relative contribution to historical anthropogenic warming has not been quantified before. Analyzing all-but-one-forcing, 20-member ensembles of historical simulations with a state-of-the-art Earth System Model, we find that over the 1955–2005 period ODSs are responsible for 30% of global warming, 37% of Arctic warming, and 33% of summertime Arctic sea ice loss. Effective Radiative Forcing (ERF) calculations reveal that the global warming response to ODSs per unit of ERF is about 20% larger than for CO₂, which may be due to stronger feedbacks and the difference in temporal evolution with ODSs having leveled off and CO₂ still increasing in 2005. While the response to both peaks in the Arctic, the ODS ERF opposes Arctic amplification more than the CO₂ ERF. Our findings highlight the importance of the Montreal Protocol for mitigating future climate change.