The ozone layer protects us all from the damage that too much UV radiation can cause to our skin and eyes. By protecting the ozone layer, the Montreal Protocol may have prevented up to 2 million cases of skin cancer each year by 2030 and avoided millions of cases of cataracts worldwide.
SDG3 highlights that ‘Ensuring healthy lives and promoting well-being at all ages is essential to sustainable development.’ Three decades before the SDGs were adopted United Nations Member States were already taking strong action to ensuring healthy lives and promote well-being through global policies to protect the ozone layer. In 1985, the text of the Vienna Convention for the Protection of the Ozone Layer begins by noting ‘the potentially harmful impact on human health and the environment through modification of the ozone layer.’ This was re-emphasised in the preamble to the Montreal Protocol which begins ‘mindful of their obligation to take appropriate measures to protect human health and the environment against adverse effects resulting or likely to result from human activities which modify or are likely to modify the ozone layer.’ Since the Montreal Protocol was adopted in 1987, its success in protecting the ozone has delivered benefits to human health and well-being that will endure for the rest of the century. This success has been documented through the quadrennial reports of the Montreal Protocol’s Environmental Effects Assessment Panel (EEAP), which is tasked with assessing human health effects as well as the wider environmental consequences of ozone depletion.
Probably the best-known contribution of the Montreal Protocol to ensuing healthy lives and promoting well-being is by preventing the very large increases in UV radiation that would have occurred with uncontrolled depletion of the stratospheric ozone layer. This is particularly pertinent to SDG target 3.4 that aims to ‘reduce by one third premature mortality from non-communicable diseases’ and specifically indicator 3.4.1 which refers to reducing the mortality rate attributed to cancer. Even now, with the successful implementation of the Montreal Protocol, skin cancers are amongst the most common forms of cancer, especially in pale-skinned populations. Uncontrolled ozone depletion would have increased the incidence of skin cancers because there are strong links between the development of the three most common forms of skin cancer (malignant melanoma, basal cell carcinoma and squamous cell carcinoma) and over-exposure to UV radiation.
Quantifying how the prevalence of skin cancers would have increased with uncontrolled ozone depletion comes from computer models of a world without the Montreal Protocol (often called the world avoided). These models combine our understanding of how ODS affect the ozone layer, of how changes in ozone affect UV radiation and how UV radiation affects the incidence of skin cancers.
World avoided models take into account that there is a time lag of years or even decades between the initial UV damage and the onset of skin cancer. Because of this time lag, the full health benefits of ozone protection policies adopted in the 1980s might not have become apparent until well into this century. One global model suggests that by 2030, the successful implementation of the Montreal Protocol will already be preventing about two million skin cancers every year, but longer-term models point to much greater benefits of ozone protection in subsequent decades. The most recent long-term world avoided model considers health impacts on people in the United States born in the years 1890-2100. This model estimates that protecting the ozone layer will have prevented approximately 443 million cases of skin cancer, including 11 million cases of malignant melanoma, resulting in approximately 2.3 million fewer skin cancer deaths, just in the USA. At present, there are no long-term world avoided models that quantify changes in the global incidence of skin cancers. However, combining existing models with the fundamental understanding of the links between skin cancers and increased UV radiation, leads to the clear conclusion that uncontrolled ozone depletion would have substantially increased the risk of skin cancers worldwide.
The recent world avoided model of the health of people born in the USA between 1890 and 2100 also indicates that failure to control ozone depletion would have led to more than 60 million additional cataract cases. As with skin cancers, the link between ozone depletion and cataracts is UV radiation, since exposure to high levels of UV radiation leads to an increased risk of cataracts. Cataracts are a very significant threat to health and well-being as they are responsible for around half of blindness worldwide. The World Health Organization already considers cataracts a priority eye disease. As with skin cancers, there are no long-term world avoided models for changes in the global incidence of cataracts without effective protection of the ozone layer. However, the existing evidence suggests that this is another major contribution of the Montreal Protocol to healthy lives and promoting, especially in regions where access to eye surgery is limited.
Although skin cancers and cataracts are probably the most well-known links between ozone protection treaties and SDG3, the Montreal Protocol’s Environmental Effects Assessment Panel (EEAP) notes others. For example, exposure to UV radiation can reduce the efficacy of vaccines, including those against bacteria (including tuberculosis) and viruses (including hepatitis B virus poliovirus, measles, and influenza). Any reduction in the effectiveness of vaccination poses a threat to SDG3.3, which aims to end epidemics of communicable diseases. Indeed, SDG3.3 includes specific indicators for reducing the incidence of both tuberculosis (indicator 3.3.2) and hepatis B (indicator 3.3.4). EEAP also note that some exposure to UV radiation is beneficial to health. One well-studied benefit is that the UV in sunlight stimulates vitamin D production in the skin. In the world we live in now, with effective protection of the ozone layer, there is a balance between the positive and negative effects of UV radiation. We can all ensure that we maximise the benefits and minimise the negative effects by avoiding excessive exposure to strong sunlight. Had we failed to protect the ozone layer that balance would have swung dramatically towards the negatives, severely hindering the delivery of SDG3.
Many ozone depleting substances (ODS), such as chlorofluorocarbons (CFCs), are very potent greenhouse gases, so by phasing out their use the Montreal Protocol has protected climate as well as the ozone layer. The reduction in ODS emissions achieved by the Protocol is already equivalent to around 135 billion tonnes of CO2. Looking to the future, modelling studies suggest that by controlling ODS emissions the Montreal Protocol will have prevented temperature increases of 4-6°C at the poles and over 2°C in the tropics by 2070. Building on that success, the Kigali Amendment to the Protocol is set to avoid another 0.4°C by controlling high global warming hydrofluorocarbons (HFCs).
The temperature increases that that will be avoided by the Montreal Protocol are similar in magnitude to those expected if we fail to control CO2 emissions. As a result, the reports of the Intergovernmental Panel on Climate Change (IPCC) give some insight in to the many ways by which temperature increases due to uncontrolled ODS emissions would have affected SDG3. For example, IPCC conclude that temperature increases over 2°C would bring an increasing risk of heat-related morbidity and mortality. The same report concludes that ‘there is very high confidence that each additional unit of warming could increase heat-related morbidity and mortality, and that adaptation would reduce the magnitude of impacts.’ While these IPPC assessments clearly focus on the unresolved challenge of warming due largely to CO2 emissions, they illustrate the likely magnitude of impacts that have been avoided by successful climate protection through the Montreal Protocol. These climate-related benefits of the Montreal Protocol for SDG3 seem likely to be substantial, although at present they are less well studied than benefits related to avoiding increased UV radiation.
Changes in stratospheric ozone have consequences for the chemistry of the lower atmosphere, including air pollution due to particulates and ground-level ozone. High concentrations of these pollutants in urban air are increasingly recognised as a major cause of ill-health, and SDG3.9 aims to ‘substantially reduce the number of deaths and illnesses from air, water and soil pollution and contamination.’ Modelling studies indicate that the gradual recovery of stratospheric ozone due to the success of the Montreal Protocol will lead to decreased air pollution in some urban areas, a further contribution to delivering SDG3.
The Montreal Protocol also stimulates research and technical innovations that contribute to SDG3. For example, the Montreal Protocol stimulated the development of experimental approaches for defining the effects of different wavelengths and intensities of ultraviolet radiation on responses ranging from sunburn and skin cancer to crop growth. These approaches have also been applied to the microorganisms that cause water-borne human diseases. The 2016 update on SDG3 notes that ‘unsafe drinking water, unsafe sanitation and lack of hygiene continue to be major contributors to global mortality, resulting in about 870,000 deaths in 2016.’ This knowledge contributes both to understanding the survival of these pathogens in lakes, rivers and the sea and to the development of solar water disinfection (SODIS), a simple technology for destroying pathogens in drinking water. This brings benefits in relation to not only SDG3 but also SDG6 Clean Water and Sanitation. The same approaches have also been applied to understanding how viruses such as Ebola or Marburg are inactivated by sunlight, understanding which has recently begun to be applied to the COVID-19 virus.