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Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.

The Environmental Effects Assessment Panel of the Montreal Protocol under the United Nations Environment Programme evaluates effects on the environment and human health that arise from changes in the stratospheric ozone layer and concomitant variations in ultraviolet (UV) radiation at the Earth’s surface. The current update is based on scientific advances that have accumulated since our last assessment (Photochem and Photobiol Sci 20(1):1–67, 2021). We also discuss how climate change affects stratospheric ozone depletion and ultraviolet radiation, and how stratospheric ozone depletion affects climate change. The resulting interlinking effects of stratospheric ozone depletion, UV radiation, and climate change are assessed in terms of air quality, carbon sinks, ecosystems, human health, and natural and synthetic materials. We further highlight potential impacts on the biosphere from extreme climate events that are occurring with increasing frequency as a consequence of climate change. These and other interactive effects are examined with respect to the benefits that the Montreal Protocol and its Amendments are providing to life on Earth by controlling the production of various substances that contribute to both stratospheric ozone depletion and climate change.

This assessment by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) provides the latest scientific update since our most recent comprehensive assessment (Photochemical and Photobiological Sciences, 2019, 18, 595–828). The interactive effects between the stratospheric ozone layer, solar ultraviolet (UV) radiation, and climate change are presented within the framework of the Montreal Protocol and the United Nations Sustainable Development Goals. We address how these global environmental changes affect the atmosphere and air quality; human health; terrestrial and aquatic ecosystems; biogeochemical cycles; and materials used in outdoor construction, solar energy technologies, and fabrics. In many cases, there is a growing influence from changes in seasonality and extreme events due to climate change. Additionally, we assess the transmission and environmental effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the COVID-19 pandemic, in the context of linkages with solar UV radiation and the Montreal Protocol.

This assessment by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) provides the latest scientific update since our most recent comprehensive assessment (Photochemical and Photobiological Sciences, 2019, 18, 595–828). The interactive effects between the stratospheric ozone layer, solar ultraviolet (UV) radiation, and climate change are presented within the framework of the Montreal Protocol and the United Nations Sustainable Development Goals. We address how these global environmental changes affect the atmosphere and air quality; human health; terrestrial and aquatic ecosystems; biogeochemical cycles; and materials used in outdoor construction, solar energy technologies, and fabrics. In many cases, there is a growing influence from changes in seasonality and extreme events due to climate change. Additionally, we assess the transmission and environmental effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the COVID-19 pandemic, in the context of linkages with solar UV radiation and the Montreal Protocol.

The Antarctic ozone hole of 2011 is reviewed from a variety of perspectives, making use of various data and analyses. The ozone hole of 2011 was relatively large in terms of maximum area, minimum ozone level and total ozone deficit, being ranked amongst the top ten in terms of severity of the 32 ozone holes adequately characterised since 1979. In particular, the estimated integrated ozone mass effectively removed within the ozone hole of 2011 was 2119 Mt, which is the 7th largest deficit on record and 82 per cent of the peak value observed in 2006. The key factors in promoting the extent of Antarctic ozone loss in 2011 were the relatively low temperatures that occurred in the lower stratosphere of the polar cap region over most of the year, and the fact that the stratospheric vortex was relatively strong and stable, at least up to mid-spring. Dynamical disturbance of the polar vortex from mid-spring increased Antarctic ozone levels in the latter part of the ozone hole’s evolution and helped to limit the overall severity of depletion. Through examination of regression of various ozone metrics against expected levels of equivalent effective stratospheric chlorine, we suggest that recent changes in averaged ozone levels over Antarctica show some evidence of the recovery expected due to international controls on the manufacture of ozone depleting chemicals, albeit at a statistically low level of confidence due to the influence of meteorological factors that largely dictate year-to-year variability of Antarctic ozone loss.

The Antarctic ozone hole of 2010 is reviewed from a variety of perspectives, making use of various data and analyses. Based on total column ozone metrics, the 2010 ozone hole was one of the smallest in the past fifteen–twenty years. The main influence on the size of the ozone hole was relatively warm temperatures in the Antarctic lower stratosphere which impeded ozone depletion in the austral spring. The warm winter temperatures were associated with a significant dynamical disturbance in the mid- and high latitude upper stratosphere during July which included a substantial warming of the mid- and upper extratropical stratosphere, a deceleration of zonal winds and a cooling in the polar mesosphere. The disturbance was likely influenced by the phase of the Quasi-Biennial Oscillation (QBO) which favoured a weak and disturbed polar vortex in the winter months. The winter warming also resulted in significant off-pole displacement and weakening of the polar vortex in the mid- to upper stratosphere, producing a long-lasting increase in the overburden of ozone and weakening ozone hole metrics based on total column ozone measurements. Ozone loss in the lower stratosphere was less markedly affected by this dynamical activity, and was similar to other recent years. A notable feature was the reduction in dynamical disturbances of the polar vortex after September, when the QBO moved into a strongly eastward phase. During the late spring and early summer, stratospheric temperatures warmed more slowly than in recent years, and this produced one of the longest-lasting ozone holes yet observed which eventually disappeared in the last week of December. The relatively low ozone levels in December resulted in unusually high surface ultraviolet fluxes as measured on the coast of East Antarctica.

The Antarctic ozone holes of 2008 and 2009 are reviewed from various perspectives, making use of a range of Australian data and analyses. In both years, ozone holes formed that were fairly typical of those observed since the late 1990s. The ozone hole of 2008 was somewhat larger than that of 2009. In 2009 the ozone hole developed more rapidly, but did not last as long as in 2008, particularly in the lower stratosphere.

The 2007 Antarctic ozone hole is reviewed from a variety of perspectives, making use of various Australian data and analyses. The 2007 ozone hole was relatively modest, particularly in comparison to that of 2006, due in part to a disturbance to the polar vortex in early September that led to an influx of ozone-rich air. Ozone depiction was still severe however in the lower stratosphere. The long-term outlook for recovery is described, with Antarctic ozone currently forecast to return to 1980 levels around the period 2055-2080.