Ozone layer is critical for planetary life, since it absorbs ultraviolet rays coming from the Sun. UV rays are known to cause skin cancer, eye cataracts, genetic and immune system damage and many other diseases and deformities in plants and animals.
Ozone layer depletion is the gradual thinning of Earth’s ozone layer in the upper atmosphere caused by the release of chemical compounds containing gaseous chlorine or bromine from industry and other human activities. Though the problem is commonly referred to as the emergence of a ‘hole’ in the ozone layer, it is actually just a reduction in concentration of the ozone molecules. The thinning is most pronounced in the polar regions, especially over Antarctica.
In the 1980s, scientists began to notice a sharp drop in the concentration of ozone. This drop was much more pronounced over the South Pole, which was later linked to the unique meteorological conditions — temperature, pressure, wind speed and direction — that prevail over Antarctica. The ozone hole over Antarctica is the biggest during the months of September, October, and November.
By the middle of 1980s, scientists had figured out that the chief cause of ozone depletion was the use of a class of industrial chemicals that contained chlorine, bromine or fluorine. The most common of these were the chlorofluorocarbons, or CFCs, that were used extensively in the air conditioning, refrigeration, paints, and furniture industries.
The global recognition of the destructive potential of CFCs led to the 1987 Montreal Protocol, a treaty phasing out the production of ozone-depleting chemicals. It is the landmark multilateral environmental agreement that regulates the production and consumption of nearly 100 man-made chemicals referred to as ozone depleting substances (ODS). The Protocol is to date one of the rare treaties to achieve universal ratification.
The Montreal Protocol phases down the consumption and production of the different ODS in a step-wise manner, with different timetables for developed and developing countries (referred to as “Article 5 countries”). Under this treaty, all parties have specific responsibilities related to the phase out of the different groups of ODS, control of ODS trade, annual reporting of data, national licensing systems to control ODS imports and exports, and other matters. Developing and developed countries have equal but differentiated responsibilities, but most importantly, both groups of countries have binding, time-targeted and measurable commitments.
In 2016, the Kigali amendment to the Montreal Protocol was agreed upon to reduce the manufacture and use of Hydrofluorocarbons (HFCs) by roughly 80-85% from their respective baselines, till 2045. This phase down is expected to arrest the global average temperature rise to 0.5o C by 2100.
The ozone hole has been steadily improving since 2000, thanks to the effective implementation of the Montreal Protocol. The latest scientific assessment has said that if current policies continued to be implemented, the ozone layer was expected to recover to 1980 values by 2066 over Antarctica, by 2045 over the Arctic, and by 2040 for the rest of the world. The success of the Montreal Protocol in repairing the ozone hole is often offered as a model for climate action. It is argued that emissions of greenhouse gases can also similarly be curtailed to arrest rapidly rising global temperatures.