Scientists working on a remote island between Tasmania and Antarctica have uncovered troubling evidence that storms in the Southern Ocean are becoming wetter and more intense, with potential consequences for weather, ocean circulation and carbon storage across the globe.
Macquarie Island, a narrow and wind-lashed ridge surrounded by open ocean, has long been known for its wildlife. Elephant seals crowd its dark beaches, king penguins cross its moss-covered slopes and albatrosses soar over its treeless hills. But the landscape itself is changing. Slopes are becoming boggier and large native plants are slowly withdrawing from areas they once dominated.
Researchers suspected increasing rainfall was responsible. A new study published in the journal Weather and Climate Dynamics confirms their suspicions and shows that the trend is part of a much wider shift in Southern Ocean climate patterns.
The island’s rainfall records, kept by the Bureau of Meteorology and the Australian Antarctic Division, are some of the most valuable in the world because very little long-term data exists in this vast and storm-dominated region. These observations stretch back more than seventy five years and are used to verify satellite measurements and computer simulations.
Scientists analysed forty five years of daily rainfall data from 1979 to 2023 and compared them with a widely used reconstruction of past weather known as the ERA5 reanalysis. They examined five different weather regimes, including low pressure systems, cold air outbreaks and incoming warm air ahead of cold fronts, to determine the true cause of rising rainfall.
The findings are striking. Annual rainfall on Macquarie Island has increased by twenty eight percent since 1979, equal to around two hundred and sixty millimetres of additional rain each year. The ERA5 model captured only a small part of this change, showing an eight percent rise.
The shift is not simply a matter of more frequent storms. Instead, storms that do occur now produce more rain. A weather pattern that brings warm air from the north has largely replaced traditional low pressure systems, but both result in wet conditions. The difference today is intensity.
This trend could have far reaching implications beyond a single island. A wetter storm belt means far more fresh water flowing into high latitude oceans. This reduces mixing between ocean layers, alters the strength of circulation and affects how nutrients and carbon move through the water. Scientists estimate that in 2023 alone the additional precipitation in these southern latitudes amounted to roughly two thousand three hundred gigatonnes of fresh water, a quantity many times greater than recent contributions from Antarctic meltwater.
The increased rainfall also changes surface salinity, potentially influencing the Southern Ocean’s role as a major carbon sink. Evaporation must increase to match the rising rainfall, cooling the ocean in the process. Researchers estimate that this evaporation-driven cooling may be ten to fifteen percent stronger now than it was in 1979.
With only one piece of solid land in the region providing long-term data, scientists consider Macquarie Island a rare “ground truth” indicator of change in one of Earth’s least observed regions. The next step is determining whether similar rainfall intensification is occurring throughout the Southern Ocean and understanding its effects on global climate systems.
Macquarie Island shows that changes in a remote wilderness can reveal major climate signals. The challenge now is to learn how these signals are shaping the planet’s stormiest ocean, and what they mean for the global climate system that billions of people rely upon.