Macquarie Island’s 75-year climate record suggests Southern Ocean storms are getting far wetter — and heat loss may exceed what models captured.
Macquarie Island is barely a speck on the map — a narrow, windswept strip of land halfway between Tasmania and Antarctica, crowded with elephant seals and king penguins. Scientists have been quietly recording its weather for more than 75 years, building one of the only long-term climate records in the entire Southern Ocean.
Now that record is showing something researchers did not expect. The island’s bogs are spreading, its native plants are retreating, and the terrain is increasingly saturated. When scientists looked closely at the data, their findings reached well beyond a single remote island.
A remote island with an outsized climate role
Macquarie Island sits roughly 1,500 kilometers southeast of Tasmania, placing it squarely inside the Southern Ocean’s relentless storm belt. That geography makes it almost uniquely valuable. With so little land in this part of the world, and nearly constant cloud cover blocking satellites, the island functions as one of the only fixed observation points scientists have in the entire region.
The Bureau of Meteorology and the Australian Antarctic Division have maintained detailed daily weather records there for more than 75 years. Researchers regularly use those records to check whether satellite data and climate models are capturing reality accurately — a process scientists call “ground truthing.” The Southern Ocean absorbs a disproportionate share of the excess heat trapped by greenhouse gases, along with a significant portion of human-produced CO₂. Any shift in how that ocean behaves does not stay local for long.
What 45 years of rainfall data revealed
To understand what was happening on the island, researchers analyzed 45 years of daily rainfall observations, covering 1979 to 2023, then compared those records against ERA5 — a widely used climate reanalysis dataset that reconstructs historical atmospheric conditions from multiple data sources.
The gap between the two was striking. On-the-ground measurements showed annual rainfall had increased by 28% since 1979 — roughly 260 millimeters of additional rain every year. ERA5 detected only an 8% increase. Standard climate tools were missing most of what was actually occurring.
Researchers then classified each day into one of five weather patterns based on pressure, humidity, wind, and temperature — among them low-pressure systems, cold-air outbreaks, and warm-air advection events.
More storms aren’t the culprit — wetter storms are
The classification exercise produced an unexpected result. Rainfall was not rising because storms were arriving more frequently; the total number of wet weather systems remained relatively stable. Instead, each storm was simply delivering more rain when it came.
One type of wet weather pattern was gradually replacing another, keeping storm counts roughly level while pushing rainfall totals higher. The Southern Ocean storm track has also shifted closer to Antarctica over time, further influencing the island’s weather. The distinction matters scientifically — climate models are generally better calibrated to detect changes in storm frequency than changes in storm intensity, so a world where storms grow wetter rather than more numerous presents a genuinely different forecasting challenge.
Freshwater flooding into the ocean — and why it matters
The consequences of heavier rainfall extend well beyond waterlogged bogs and retreating vegetation. All that extra rain is freshwater entering the upper layers of the Southern Ocean, and the volumes involved are substantial. Researchers estimate that by 2023, the additional rainfall was contributing roughly 2,300 gigatonnes of freshwater per year across the high-latitude Southern Ocean — a figure that dwarfs recent freshwater inputs from Antarctic meltwater, with the gap continuing to grow.
Freshwater is less dense than saltwater. When it accumulates at the surface, it strengthens the separation between ocean layers, reducing the vertical mixing that transports heat, nutrients, and carbon between surface and deep water. Disruptions to that process could affect how efficiently the ocean draws down atmospheric CO₂.
The Southern Ocean is ‘sweating’ — and cooling itself differently
More rainfall requires more evaporation to fuel it. Evaporation pulls heat directly from the ocean surface — the same mechanism by which sweat cools the human body. In the persistently cloudy Southern Ocean, where sunlight is limited, evaporation is one of the primary ways the ocean sheds heat.
The study estimates that the Southern Ocean may now be cooling itself through evaporation 10 to 15% more than it did in 1979. Researchers describe this as the ocean “sweating” more as the climate warms — a feedback that existing models have not fully accounted for. Whether this extends across the entire Southern Ocean storm belt remains an open question, though multiple lines of evidence suggest it may. If confirmed at that scale, the implications for global heat distribution and ocean circulation would be significant.
The next step, researchers say, is determining how widespread these rainfall changes actually are and building that understanding into the models governments and policymakers rely on. Macquarie Island has been quietly keeping records for decades — and what those records reveal suggests the scientific community may need to pay much closer attention to the world’s stormiest and most overlooked ocean.