The hole in the ozone layer has begun to form early this year, prompting warnings that a larger-than-average hole may further warm the Southern Ocean while the level of Antarctic sea ice is at a record low. Satellite data from the European Centre for Medium-Range Weather Forecasts suggests the hole has already begun to form over Antarctica. Dr Martin Jucker, a lecturer at the Climate Change Research Centre at the University of New South Wales, said the hole usually began forming at the end of September, peaking in October before closing in November or December. Sign up for Guardian Australia’s free morning and afternoon email newsletters for your daily news roundup “Starting in August is certainly very early,” he said. “We don’t usually expect that.” The Antarctic ozone hole is an annual thinning of the stratosphere’s ozone layer, which has a high concentration of ozone molecules that absorb ultraviolet radiation from the sun. The hole has been “healing” over time, following the 1989 Montreal protocol which eliminated 99% of ozone-depleting chemicals, such as chlorofluorocarbons. Ozone levels over the Antarctic are expected to bounce back to 1980 levels by 2066. The ozone hole is usually smaller during El Niño years, but modelling by Jucker and collaborators, including Chris Lucas of the Australian Bureau of Meteorology, has suggested it will be larger than usual in 2023, due to long-lasting atmospheric changes after the undersea Tonga volcano explosion in January last year. The modelling has not yet been peer-reviewed. Lucas, a senior research scientist at the BoM, said early indications showed the Antarctic ozone hole was beginning to form. “As of 4 August, the NASA ozone hole webpage suggests the formation is currently about ‘average’ for the day of the year,” he said. “Some forecasts expect this to increase rapidly, in the next few days, producing one of the largest (for the time of year) observed ozone holes.” “The most rapid growth of the ozone hole occurred in the year 2000. The event developing appears comparable to this right now.” The eruption of the Hunga Tonga-Hunga Ha’apai volcano injected “an unprecedented amount” of water vapour into the stratosphere, Jucker said – about 150 megatonnes. “It’s a factor of about three times more water vapour than we usually have.” Ice clouds form in the stratosphere when there is more water vapour than usual, allowing ozone-destroying molecules to gather on ice particles. Jucker said he was concerned about the impact of the hole on Antarctic sea ice, which has hit record lows over the past two years. “The more UV radiation that reaches Antarctica [and] the Southern Ocean means that there is more energy available to melt ice,” Jucker said. “Now that we have so little sea ice, instead of [reflective] white ice there is very dark blue ocean. “There is a risk that the Southern Ocean would then heat up even more and then indirectly melt more ice because the water next to the ice is warmer.” A larger ozone hole may also lead to a positive phase of a climate driver called the southern annular mode (Sam). “A positive Sam would shift … winds further poleward,” Jucker said. “Stronger winds come further to[wards] the pole and they can push away more ice.” Eun-Pa Lim, a senior research scientist at the BoM, said there was “large uncertainty in which direction the Sam will swing in spring and summer at this stage”, because an El Niño could push the Sam towards a negative phase. “It is also uncertain how the current early development of the Antarctic ozone hole will impact the Antarctic sea ice via a change in Sam.” Other impacts from the Tonga volcano eruption – such as higher-than-usual surface temperatures over large regions of the world – are expected to continue until the end of the decade. The eruption would temporarily compound the impacts of greenhouse gas emissions on global heating, Jucker said. “At least that effect will go away – it’s not like climate change which will stick around for centuries, but it’s an additional thing.”