For years, scientists suspected the culprit was increasing rainfall<\/a>. Our new research<\/a>, published in Weather and Climate Dynamics, confirms this \u2013 and shows the story goes far beyond one remote UNESCO World Heritage site.<\/p>\n A major \u2013 but little observed \u2013 climate player<\/p>\n The Southern Ocean plays an enormous role in the global climate system. <\/p>\n It absorbs much of the excess heat<\/a> trapped by greenhouse gases and a large share of the carbon dioxide emitted by human activity. <\/p>\n Storms in the Southern Ocean also influence weather patterns across Australia, New Zealand and the globe. <\/p>\n Yet it is also one of the least observed places on Earth. <\/p>\n With almost no land masses, only a handful of weather stations, and ubiquitous cloud cover, satellites and simulations struggle to capture what is actually happening there. <\/p>\n That makes Macquarie Island\u2019s climate record from the Bureau of Meteorology and the Australian Antarctic Division exceptionally valuable, providing one of the very few long-term \u201cground truth\u201d records anywhere in the Southern Ocean.<\/p>\n These high-quality records of the observed daily rainfall and meteorology date back more than 75 years and are commonly used to validate satellite products<\/a> and numerical simulations. <\/p>\n Macquarie Island is a tiny speck of land in the Southern Ocean. Rising rainfall<\/p>\n Earlier<\/a> work<\/a> has found rainfall at Macquarie Island had risen sharply over recent decades, and ecologists<\/a> documented waterlogging that harms native vegetation. <\/p>\n But no one has explained how the island\u2019s weather patterns are changing, or directly compared the field observations to our best reconstructions of past weather to assess Southern Ocean climate trends.<\/p>\n To fill this gap, we analysed 45 years (1979\u20132023) of daily rainfall observations and compared them to a widely used reconstruction of earlier weather, known as the ERA5 reanalysis.<\/p>\n We wanted to understand the meteorology behind the increase in rainfall \u2013 that is, whether it was caused by more storms or more intense rainfall during storms. To do this we placed each day in the dataset into one of five synoptic regimes based on pressure, humidity, winds and temperature. <\/p>\n These regimes included low pressure systems, cold-air outbreaks and warm-air advection (the warm air that moves poleward ahead of a cold front). <\/p>\n Storms are producing more rain<\/p>\n Our analysis showed that annual rainfall on Macquarie Island has increased 28% since 1979 \u2013 around 260 millimetres per year. <\/p>\n The ERA5 reanalysis, in contrast, shows only an 8% increase \u2014 missing most of this change. <\/p>\n The storm track\u2019s gradual move toward Antarctica is well established<\/a>, and our results show how this larger change is shaping Macquarie Island\u2019s weather today.<\/p>\n Crucially, we found that these changes are not causing the increase in rainfall, as one wet regime (warm air advection) was largely replacing another (low pressure). <\/p>\n Instead, storms now produce more rain when they occur. <\/p>\n Elephant seals on Macquarie Island. Why does this matter beyond one island?<\/p>\n If the rainfall intensification we see at Macquarie Island reflects conditions across the Southern Ocean storm belt \u2013 as multiple<\/a> lines<\/a> of evidence indicate \u2014 the consequences are profound.<\/p>\n A wetter storm track means more fresh water entering the upper ocean. This strengthens the different layers in the oceans and reduces the amount of mixing that occurs. In turn, this alters the strength of ocean currents.<\/p>\n Our estimate suggests that in 2023 this additional precipitation equates to roughly 2,300 gigatonnes of additional freshwater per year across the high-latitude Southern Ocean \u2013 an order of magnitude greater than recent Antarctic meltwater<\/a> contributions. And this difference continues to grow. <\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2025\/12\/file-20251204-56-1aoswr.jpg\")
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\n David Killick\/AP<\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2025\/12\/file-20251203-56-6vbvey.png\")
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\n Kita Williams<\/p>\n