CFC emissions, which directly impact the ozone layer, are increasing again. This opinion piece, written by Dr Anna Lewis and Senior Professor Sharon Robinson, highlights the ways in which ozone depletion has impacted climate, ecosystems and wildlife in the Southern Hemisphere.
F ollowing international ratification of the Montreal Protocol in 1987, it was expected that continued chloroflurocarbon (CFC) reduction would allow the ozone layer to effectively recover over the next few decades (by 2065). However, it was recently found that ozone-depleting chemical emissions are on the rise again, despite a worldwide global ban since 2010.
CFCs are nontoxic, non-flammable chemicals that are cheap and readily available. Before being banned, CFCs were commonly utilised as a propellant in aerosol sprays, blowing agents for foams and packing materials, and refrigerants.
When the Montreal Protocol was first enacted in the 1970s, the key concern from depletion of the ozone layer was the negative effect of ultraviolet-B radiation on ecosystems. Over the past decade, scientists have discovered that the overall climatic effects are also a major concern for the health of ecosystems rather than simply ultraviolet-B radiation alone. The impacts of these climatic changes on the environment have only become apparent over the past few years.
A paper recently published in Nature Sustainability reviews how the hole in the ozone layer above Antarctica actually influences climate. In turn, this change in climate affects ecosystem health and biodiversity in the Southern Hemisphere. The Southern Hemisphere is affected more strongly by ozone depletion than the Northern Hemisphere. This is because Antarctica has optimal cool conditions at high altitudes for CFCs to act as catalysts and break down ozone in the stratosphere.
Ozone depletion has shifted the major climate zones of the Southern Hemisphere south. In particular, the jet stream has shifted closer to Antarctica. The hole in the ozone layer acts as a ‘pull’, and greenhouse gases as a ‘push’ factor for this southerly climate shift. This mode of climate variability is represented by the Southern Annular Mode (SAM), with positive SAM conditions indicating a more southerly jet stream (and the associated polar and ferrel climate cells). The SAM is now the most positive it has been in more than 1,000 years. We know this due to studies of ice cores in Antarctica.
This climate variability has altered wind, rainfall, and temperature patterns across the Southern Hemisphere. Ocean currents across the Southern Hemisphere, such as the Eastern Australian Current, have also been altered, which in turn affects ocean productivity. Typically, cooler oceans are more productive and support more life, including increased fish stocks in fisheries, yet warmer oceans are less productive.
In general, the most pronounced effects to terrestrial ecosystems are seen in southern regions of New Zealand, South America and Australia. South-west coast regions are now prone to drying (for example, south-west Chile), which reduces productivity, with wetter conditions more commonplace on the opposite eastern coasts (southern Brazil), supporting healthy forests and agriculture.
So, as a result of these climatic changes, some regions and individual species benefit, while others are disadvantaged. Species that have benefited in more productive regions include four species of penguin, as well as wandering albatross and elephant seals. For them, ozone depletion has been beneficial with regard to their growth, survival and reproduction. The four different species of penguin, including the Adélie penguin, have had increased breeding success, likely driven by increases in food supplies in the regions they inhabit.
The same can be said for elephant seals which have been found to have an increased maternal body size for similar reasons. The albatross show an increased female body mass which is linked to better reproductive outcomes. This is likely because it has become windier where they live, meaning they can soar and glide further and thus expend less energy finding food.
Typically, cooler oceans are more productive and support more life, including increased fish stocks in fisheries, yet warmer oceans are less productive.
In contrast, kelp beds off Tasmania and corals off the coast of Brazil show declines as the climate shifts to warmer sea surface temperatures. Endemic cushion plants from Macquarie Island in the Southern Ocean, estimated to be hundreds of years old, are dying due to windier and drier conditions. Ancient moss beds near Casey Station in East Antarctica have also dried out as summers have become cooler and windier over recent decades. However, many impacts to animal and plants have yet to be measured, particularly in those areas where productivity maybe declining.
It is concerning that ozone-depleting substances are on the rebound globally, as actions under the Montreal Protocol have been greatly beneficial in moderating climatic and subsequent ecosystem changes. The Montreal Protocol is doing more to mitigate global climate change than any other human action to date.
As the ozone ‘hole’ recovers, some of the effects of human-induced climate change may be reversed. It is therefore important to continue to abide by the Montreal Protocol, because in addition to reducing our exposure to UV radiation, the ozone layer also drives weather patterns, in-turn affecting biodiversity in the Southern Hemisphere.
Dr Anna Lewis is a Research Officer, Sustaining Coastal and Marine Zones, for Global Challenges. Senior Professor Sharon Robinson is the Challenge Lead, Sustaining Coastal and Marine Zones, for Global Challenges, and is also a United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel Member since 2009.