Reduction in surface climate change achieved by the 1987 Montreal Protocol

Abstract

The benefits of the 1987 Montreal Protocol in reducing chlorofluorocarbon emissions, repairing the stratospheric ozone hole, shielding incoming UV radiation, reducing the incidence of skin cancer and mitigating negative ecosystem effects are all well documented. Projected future climate impacts have also been described, mainly focused on a reduced impact of the mid-latitude jet as the ozone hole gradually repairs. However, there is little appreciation of the surface warming that has been avoided as a result of the Montreal Protocol, despite CFCs being potent greenhouse gases. Instead, the issue of ozone depletion and climate change are often thought of as two distinct problems, even though both ozone and CFCs impact Earth's radiation budget. Here we show that a substantial amount of warming has been avoided because of the Montreal Protocol, even after factoring in the surface cooling associated with stratospheric ozone depletion. As of today, as much as 1.1°C warming has been avoided over parts of the Arctic. Future climate benefits are even stronger, with 3°C-4°C Arctic warming and ∼1°C global average warming avoided by 2050; corresponding to a ∼25% mitigation of global warming. The Montreal Protocol has thus not only been a major success in repairing the stratospheric ozone hole, it has also achieved substantial mitigation of anthropogenic climate change both today and into the future.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…Building on earlier work [ 6 , 8 , 9 ], Goyal et al [ 10 ] recently re-evaluated the amount of global warming that has been avoided due to the Montreal Protocol. This new study is based on a coupled atmosphere–ocean–land–sea–ice model and took into account the effect of the Montreal Protocol on emissions of ODSs that have contributed the most to stratospheric chlorine concentrations, namely the chlorofluorocarbons (CFCs) CFC-11 and CFC-12, as well as the CFC substitutes HCFC-22, HFC-125 and HFC-134a.…”

“…As much as 1.1 °C warming has been avoided over parts of the Arctic. In addition to quantifying benefits from the Montreal Protocol that have already been realised, Goyal et al [ 10 ] also assessed the Montreal Protocol’s effect on the future climate for the RCP 8.5 scenario. Projected temperature increases that are likely to be averted by 2050 are on the order of 1.5 °C to 2 °C over most extrapolar land areas, and between 3 °C and 4 °C over the Arctic.…”

“…Like previous assessments [ 6 , 8 , 9 ], the studies by Goyal et al [ 10 ] and Polvani et al [ 3 ] took into account that ozone is also a GHG. Depletion of stratospheric ozone resulting from ODSs has therefore led to a small radiative cooling at the surface.…”

“…However, both studies concluded that the magnitude of surface warming by ODSs far outweighs the cooling effect from ozone depletion. In a more recent multi-model study, Morgenstern et al [ 12 ] estimated a larger cooling effect from ozone depletion than modelled by Goyal et al [ 10 ] and Polvani et al . [ 3 ].…”

Spatial variations in the warming trend and the transition to more severe weather in midlatitudes

“…The importance of the Montreal Protocol to the slowdown observed and the future warming at the global and regional scales has been recognized, with a global cooling effect near 0.1 °C in 2013 and about 1.0 °C in 2050 3 , 48 – 51 . The Montreal Protocol has been hailed as the most effective international effort to date for reducing global warming 29 , 50 .…”