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.