Guest essay by Eric Worrall
How saving the ozone layer in 1987 slowed global warming
by Alvin Stone, University of New South Wales
The Montreal Protocol, an international agreement signed in 1987 to stop chlorofluorocarbons (CFCs) destroying the ozone layer, now appears to be the first international treaty to successfully slow the rate of global warming.
New research published today in Environmental Research Letters has revealed that thanks to the Protocol, today’s global temperatures are considerably lower. And by mid-century the Earth will be—on average—at least 1°C cooler than it would have been without the agreement. Mitigation is even greater in regions such as the Arctic, where the avoided warming will be as much as 3°C—4°C.
“By mass CFCs are thousands of times more potent a greenhouse gas compared to CO2, so the Montreal Protocol not only saved the ozone layer but it also mitigated a substantial fraction of global warming,” said lead author of the paper Rishav Goyal.
“Remarkably, the Protocol has had a far greater impact on global warming than the Kyoto Agreement, which was specifically designed to reduce greenhouse gases. Action taken as part of the Kyoto Agreement will only reduce temperatures by 0.12°C by the middle of the century—compared to a full 1°C of mitigation from the Montreal Protocol.”
Looking ahead, co-author Prof Matthew England said, “The success of the Montreal Protocol demonstrates superbly that international treaties to limit greenhouse gas emissions really do work; they can impact our climate in very favourable ways, and they can help us avoid dangerous levels of climate change.
“Montreal sorted out CFC’s, the next big target has to be zeroing out our emissions of carbon dioxide.”Read more: https://phys.org/news/2019-12-ozone-layer-global.html
The abstract of the study is below.
Reduction in surface climate change achieved by the 1987 Montreal Protocol
Rishav Goyal, Matthew H England, Alex Sen Gupta and Martin Jucker
Published 6 December 2019
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.Read more: https://iopscience.iop.org/article/10.1088/1748-9326/ab4874
In the body of the study the authors describe how their study is based on RCP 8.5.
… The main comparison evaluated in our study is between the No Protocol and RCP8.5 simulations, to give an estimate of the overall surface warming mitigation achieved by the Montreal Protocol. …
What do you think of this attempt to rehabilitate RCP 8.5? (see correction)
Update (EW): Included an explanation of the reference to RCP 8.5
Correction (EW): Nick Stokes points out that this isn’t an attempt to rehabilitate RCP 8.5, the assumption of the authors is RCP 8.5 (which includes their CFC effect) would have been even wilder without the Montreal Protocol.