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International agreements – such as the Montreal Protocol and associated Kigali Amendment - have been largely successful in reducing emissions of ozone depleting substances. However, in recent years, some of these emissions have been observed to increase once more. These renewed, unreported emissions raise questions about potential gaps in international agreements and associated scientific monitoring. In this collection, we bring together both research articles on the physical evidence for renewed emissions and their consequences, as well as opinion articles outlining important next steps to secure a recovery of stratospheric ozone.
The Montreal Protocol has begun to heal the Antarctic ozone hole and avoided more global warming than any other treaty. Still, recent research shows that new unexpected emissions of several chlorofluorocarbons, carbon tetrachloride, and hydrofluorocarbons, are undermining the Protocol’s success. It is time for policymakers to plug the holes in the ozone hole treaty.
International agreements have been implemented to reduce emissions of hydrofluorocarbons (HFCs) to reduce their radiative forcing. Even though reported HFC-23 emissions are at a historical low, observations indicate that emissions have actually increased over recent years to higher levels than previously.
Following international agreements, the use of chlorofluorocarbons in production is supposed to be phased out. Here, the authors present a new estimate of these products already in use and their emissions and show that they are larger than expected and that not recovering these banks leads to a substantial delay in the polar ozone hole recovery.
New, non-compliant emissions of ozone-depleting substances and very short-lived substances challenge the continued success of the Montreal Protocol, and, thereby, the timescale for the recovery of the ozone layer. This Review discusses recent trends in anthropogenic and natural ozone-depleting substance and very short-lived substance emissions, and examines their potential impact on atmospheric ozone concentrations.
Atmospheric data and chemical-transport modelling show that CFC-11 emissions from eastern China have again decreased, after increasing in 2013–2017, and a delay in ozone-layer recovery has probably been avoided.
Atmospheric concentration measurements at remote sites around the world reveal an accelerated decline in the global mean CFC-11 concentration during 2018 and 2019, reversing recent trends and building confidence in the timely recovery of the stratospheric ozone layer.
The production of chlorofluorocarbons (CFC) was phased-out under the Montreal, but renewed emissions of CFC-11 have been reported recently. Here, the authors present a joint analysis of multiple factors and find that emissions of CFC-11, but also CFC-12 and CFC-113 are higher than expected, indicating renewed emissions.
Recovery of the stratospheric ozone layer above Antarctica has not been straightforward, as a result of human activities and climate change. The recovery process might be delayed by up to decades if further mitigation actions are not taken.
The Antarctic ozone hole is decreasing in size due to policies implemented following the Montreal Protocol. Here, model simulations show that if recently discovered increase in unreported CFC-11 emissions continue, they could delay the recovery of the ozone hole by well over a decade.
Arctic warming is attributed to GHGs and feedbacks, but the specific contribution of ozone-depleting substances (ODS)—also potent GHGs—has never been quantified. Here, model simulations suggest ODS contributed 0.8°C of Arctic warming and led to considerable sea-ice loss during the period 1955–2005. [This summary has been amended to reflect the addendum published 28 January 2020]
In the upper atmosphere, ozone is essential to protect the planet through absorption of ultraviolet radiation; but at ground level, ozone is a pollutant, and increasing anthropogenic emissions are resulting in higher levels. Reducing emissions would mitigate the harmful effects of ozone as well as potentially increasing a natural carbon sink.
The recovery of stratospheric ozone in the Southern Hemisphere in the wake of the Montreal Protocol is driving a pause in atmospheric circulation trends that warrants closer scrutiny across the Earth system.