The ozone layer protects life below water from damage caused by too much UV radiation. By protecting the ozone layer, the Montreal Protocol helps to protect aquatic resources, which in turn protect food supplies and the economies of countries and sectors that rely on those resources.

The Montreal Protocol helps to achieve SDG14 aims that include to ‘sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts, including by strengthening their resilience, and take action for their restoration in order to achieve healthy and productive oceans’ (Target 14.2). 

Just as excess UV radiation can damage human health, it is clear that it can have multiple effects on many aquatic organisms. The successful implementation of the Montreal Protocol has protected Life below Water (SDG14) by preventing the very large increases in UV radiation that would have occurred without the effective protection provided by the stratospheric ozone layer. 

Phytoplankton and seaweeds need sunlight for photosynthesis, so they cannot avoid exposure to UV radiation. However, these organisms have evolved systems that reduce or repair UV damage, including producing pigments that act as sunscreens. Phytoplankton may gain some protection because the constant mixing of the oceans moves them deeper in to the water. UV damage to seaweeds and phytoplankton, which are the primary producers in aquatic ecosystems, would have had severe knock-on effects on animals across the whole food-web. UV radiation also directly damages multiple aspects of the biology of zooplankton, which are often the key link between primary producers and larger animals such as fish. Some zooplankton produce sunscreens or are able to swim into shaded or deeper water to avoid UV radiation, but even species from tropical regions appear to be vulnerable to UV damage. Fish may also be able to sense and avoid high UV radiation, but the larvae of many commercially important species are sensitive to damage caused by UV radiation. As a result of the vulnerability of many aquatic organisms to UV radiation, uncontrolled ozone depletion would have threatened the productivity of fisheries that are a vital source of food around the world.  

The Montreal Protocol has already made a large contribution to protecting the climate by phasing-out ozone depleting substances, such as chlorofluorocarbons (CFCs), that are also very potent greenhouse gases. 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 have been 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) gives some insight to how the temperature increases avoided by the Protocol would have affected SDG14. For example, IPCC highlight a very high risk of damage to fish, some shellfish, and warm water corals from temperature increases of 2°C or more. Fisheries at low latitudes are assessed to be at high risk from such warming. IPCC also conclude that temperature increases over 2°C brings a very high risk of severe impacts in the Arctic region. The Arctic and its indigenous people is one of IPCC’s ‘unique and threatened systems’ that are at very high risk of severe impact. The 2019 IPPC report on the cryosphere highlight the risks at high latitudes. These risks include extensive loss of sea-ice, changes in the distribution of biomes and in the range and abundance of individual species.  

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 Protocol in protecting Life below Water seems likely to be substantial, although most remain less well studied than benefits related to avoiding increased UV radiation. The one exception is the growing understanding of the ecological effects of on-going changes in climate in the Southern hemisphere that are linked to the Antarctic ozone hole. Stratospheric ozone depletion has contributed to changes in Southern Ocean temperature and circulation. The ecological consequences of these changes vary between regions, but include effects on organisms as diverse as seaweeds, elephant seals, penguins and lobsters.