Antarctic ozone hole starts amid questions about the impact of hunga tonga eruption

The monitoring of the early stages of the Ozone Hole over the South Pole during 2023 by the Copernicus Atmosphere Monitoring Service (CAMS)has detected a slightly earlier development. Lower ozone column values in comparison to the previous 43 years of satellite observations, together with other key indicators, mark an early start to the ozone hole this year. However, the evolution observed over the last week and the CAMS forecast for the coming days show that the situation is coming closer to the average. The early formation is possibly related to the impact that the January 2022 eruption of the Hunga-Tonga-Hunga Ha’apai volcano had on the composition of the upper atmosphere. It is an open question whether it will lead to stronger ozone depletion and a larger than usual ozone hole for 2023.

The Antarctic ozone hole is an atmospheric phenomenon that occurs during spring each year. Under normal conditions in the Southern Hemisphere stratosphere the hole starts to form in mid- to late August, as the Sun rises over the South Pole, and closes towards the end of November. The combination of the ERA-5 and CAMS reanalyses provides a 43-year dataset of total column ozone (TCO3) giving context to each year’s development. In 2023 the development has started unusually early following some of the lowest minimum total column ozone values for the Southern Hemisphere in the last four decades throughout July. Because of this, its total area is currently relatively high, although its progression has followed a fairly typical pattern of growth.

One of the potential reasons that could explain this unusual start of the ozone hole season is the increase in water vapour brought to the atmosphere by the eruption of the Hunga Tonga volcano in December 2021 and January 2022. This mechanism takes place because ozone depletion is fuelled by chemical processes occurring on polar stratospheric clouds, which are more likely to form when water vapor levels on the stratosphere are high.

The long-lived Ozone Depleting Substances (ODS) that have accumulated in the stratosphere and cause a drastic decrease of ozone concentration over Antarctica in Spring each year are mainly of human origin and had been emitted by a range of industries since the 1960s. Since the adoption of the Montreal Protocol in 1987, which phased out new emissions, ODS concentrations in the stratosphere have curbed and there are significant signs of recovery of the ozone layer. It is important to note that ODS will affect the ozone layer for many decades as it takes a long time for these to be eventually removed from the atmosphere. It is expected that in 50 years their concentrations in the stratosphere will have returned to the pre-industrial levels and ozone holes will no longer be experienced.

CAMS Director, Vincent-Henri Peuch comments: “Our ability to provide three-dimensional analyses and forecasts of the ozone in the poles is a powerful approach to monitor in real time how ozone holes develop, and to assess what are the key drivers behind what is being observed. This gives us insights about the extent to which particular events affect this year’s development of the Antarctic ozone hole, such as the Hunga Tonga-Hunga Ha’apai eruption of last year that increased the amount of water vapour in the stratosphere. It is currently indeed an open question for scientists, and CAMS will continue to provide its detailed monitoring information until the 2023 ozone hole dissolves later in November or December."

The Copernicus Atmosphere Monitoring Service (CAMS), implemented by the European Centre for Medium-Range Weather Forecasts on behalf of the European Commission with funding from the European Union, supports international efforts to preserve the ozone layer through its continual monitoring and provision of data on its current state.