Confirming the substantial contribution of ozone-depleting halocarbon emissions to global warming during the second half of the 20th century

Friedel, M. and Chiodo, G. and Weber, K. and Polvani, L. M. and Daniel, J. S. and Abraham, N. L. and Davis, S. M. and Deushi, M. and Oshima, N. and Horowitz, L. W. and Lamarque, J. F. and Keeble, J. and Nazarenko, L. and Orbe, C. (2026) Confirming the substantial contribution of ozone-depleting halocarbon emissions to global warming during the second half of the 20th century. npj Climate and Atmospheric Science, 9 (1): 106. ISSN 2397-3722

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Abstract

Ozone-depleting halocarbons (OD-HCs) are potent greenhouse gases but can also cause radiative cooling by depleting stratospheric ozone. Previously, global climate models revealed substantial OD-HC-driven warming in the second half of the 20th century, with only partial offset by ozone loss. More recent estimates of OD-HC net effective radiative forcing (ERF), however, have raised the possibility of much larger cancellation from ozone depletion, questioning the climatic co-benefits of the Montreal Protocol, which led to the worldwide phase-out of OD-HCs. Here, analyzing several comprehensive chemistry-climate models with realistic stratospheric ozone depletion, we confirm that the OD-HC net ERF is extremely likely positive, with a best estimate of ~ 0.2 W m−2 for 2014, consistent with earlier estimates showing only a partial offset by ozone depletion. Furthermore, our results demonstrate that, had OD-HC emissions not occurred in the second half of the 20th century, global warming during that period would have been around 20% lower, confirming the critical co-benefit of the Montreal Protocol in mitigating global warming.