Environmental consequences of interacting effects of changes in stratospheric ozone, ultraviolet radiation, and climate: UNEP Environmental Effects Assessment Panel, Update 2024

Abstract

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) addresses the interacting effects of changes in stratospheric ozone, solar ultraviolet (UV) radiation, and climate on the environment and human health. These include new modelling studies that confirm the benefits of the Montreal Protocol in protecting the stratospheric ozone layer and its role in maintaining a stable climate, both at low and high latitudes. We also provide an update on projected levels of solar UV-radiation during the twenty-first century. Potential environmental consequences of climate intervention scenarios are also briefly discussed, illustrating the large uncertainties of, for example, Stratospheric Aerosol Injection (SAI). Modelling studies predict that, although SAI would cool the Earth's surface, other climate factors would be affected, including stratospheric ozone depletion and precipitation patterns. The contribution to global warming of replacements for ozone-depleting substances (ODS) are assessed. With respect to the breakdown products of chemicals under the purview of the Montreal Protocol, the risks to ecosystem and human health from the formation of trifluoroacetic acid (TFA) as a degradation product of ODS replacements are currently de minimis. UV-radiation and climate change continue to have complex interactive effects on the environment due largely to human activities. UV-radiation, other weathering factors, and microbial action contribute significantly to the breakdown of plastic waste in the environment, and in affecting transport, fate, and toxicity of the plastics in terrestrial and aquatic ecosystems, and the atmosphere. Sustainability demands continue to drive industry innovations to mitigate environmental consequences of the use and disposal of plastic and plastic-containing materials. Terrestrial ecosystems in alpine and polar environments are increasingly being exposed to enhanced UV-radiation due to earlier seasonal snow and ice melt because of climate warming and extended periods of ozone depletion. Solar radiation, including UV-radiation, also contributes to the decomposition of dead plant material, which affects nutrient cycling, carbon storage, emission of greenhouse gases, and soil fertility. In aquatic ecosystems, loss of ice cover is increasing the area of polar oceans exposed to UV-radiation with possible negative effects on phytoplankton productivity. However, modelling studies of Arctic Ocean circulation suggests that phytoplankton are circulating to progressively deeper ocean layers with less UV irradiation. Human health is also modified by climate change and behaviour patterns, resulting in changes in exposure to UV-radiation with harmful or beneficial effects depending on conditions and skin type. For example, incidence of melanoma has been associated with increased air temperature, which affects time spent outdoors and thus exposure to UV-radiation. Overall, implementation of the Montreal Protocol and its Amendments has mitigated the deleterious effects of high levels of UV-radiation and global warming for both environmental and human health.

Fig. 1

Geographical distribution of the annual-mean difference in precipitation between the “no Montreal Protocol” simulation and a simulation based on the “middle of the road” (SSP2-4.5, see footnote 1) pathway of greenhouse gas emissions, averaged over the period 2090–2100 (in %). Green areas indicate increased precipitation that would have occurred without the Montreal Protocol, whilst brown areas indicate decreases. Areas where the statistical significance of the signal is less than 90% are marked by dots. [4] Reproduced from Egorova et al.

Fig. 2

Modelled effect of the increased stratospheric water vapour concentration from the HTHH eruption on total ozone anomalies over the 2022–2031 period. Contour intervals are − 5 DU and include the ± 1 DU contours to show minor effects. Since these model calculations only quantify the effect of water vapour and not aerosols from the HTHH eruption, the full effect on total column ozone may be somewhat underestimated, at least in the first year following the eruption. Reproduced from [23] with permission from the author

Fig. 3

Estimated changes in global mortality as reported by Moch et al. [69] (green bars) and re-examined here (blue bars, light or dark fills showing the range of the estimates)

Fig. 4

Modelled trends in tropospheric ozone with and without halogen chemistry (solid and dotted lines, respectively) for the Representative Concentration Pathways RCP6.0 and RCP8.5 (blue and red lines, respectively). Shading under traces indicate different definitions of the tropopause. RCP6.0 and RCP8.5 are representative greenhouse gas concentration pathways, which lead to radiative forcing of ca 6.0 W m⁻² and 8.5 W m⁻², respectively, by 2100 and global average surface temperature rises of ca 3 °C and 4 °C, respectively [82], reproduced from [80]

Fig. 5

A cumulative frequency distribution of combined data from all measurements of TFA in the River Rhine (2017–2022). Data from the RIWA reports for 2017 to 2023 (n = 297) [–107]

Fig. 6

Flux of TFA in the river Rhine estimated from reported concentrations and flow rate at Lobith using data from RIWA reports for 2017–2023 [–107]. The line through the data is a linear least-squares fit which has a slope of 2.8 ± 3.2 tonnes year⁻¹

Fig. 7

Interacting environmental processes affecting the formation of plastic particles and degradation products (such as additives) and their effects in the environment. Photo-oxidation and biological metabolism can both contribute to plastic degradation, and ultimately fragmentation. Plastic fragments and leached additives can negatively affect ecosystem processes, and organisms including humans. The finding of UV-radiation-induced persistent free radicals (i.e., reactive species present on the surface of plastics) further implicates exposure to UV-radiation with toxic effects on living organisms

Fig. 8

Conceptual diagram illustrating the cycle between the design, production, use, and disposal of materials. Products are intentionally designed for a specific need. To impart specific properties to the materials, manufacture processes involve, for instance, use of additives. Materials in outdoor use are exposed to solar UV-radiation and other weathering agents that cause ageing. Deterioration following ageing leads to post-use consequences that should be addressed by modifying the manufacture processes

Fig. 9

(a) The exposure of dead plant material (plant litter) to solar radiation and precipitation promotes photodegradation through different mechanisms. Changes in climate and land use will shift the dominance of these processes, altering the rate of litter decomposition and consequently the rate of carbon turnover in terrestrial ecosystems. (b) A laboratory study under controlled conditions has found that the hydrogen peroxide (H₂O₂) produced during photodegradation of lignin activates microbial enzymes in dead plant material (e.g. lytic polysaccharide monooxygenases—LPMO), generating carbohydrates such as saccharose. If operating in the environment, this may illustrate how the aspects of photodegradation driven by UV-B, UV-A, and blue light interact. This understanding will allow us to better assess the effects of ozone depletion on photodegradation, and thus to model the consequences for terrestrial ecosystems

Fig. 10

Climate change effects on the exposure of phytoplankton in the Arctic Ocean to UV-radiation. (a) Expansion of the late winter (May) open water area of the Arctic Ocean. White area shows extent of ice retreat between 1980 and 2024 mostly in the Barents Sea. Concurrently from 1980 (b) to 2018 (c circulation models indicate that the depth of the surface mixed layer (light blue) is increasing, reducing average exposure to UV-radiation in the mixed layer, even though the UV-radiation at the surface is increasing due to the reduction in ice cover

Fig. 11

Effects of exposure to UV-B radiation on dengue infection of mosquitos. (a) Low survival of mosquito larvae exposed to low intensity UV-B radiation (UV Index = 1.6), (b) high incidence of dengue infection when surviving females are fed blood with the virus, and (c) these mosquitos can spread dengue infections to humans. DENV dengue virus