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

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.