A climate lifeline under threat
Northern Australia’s wet season is a welcome sight for farmers and ecosystems, delivering critical rainfall that revitalises crops and livestock. But a new study of tree pollen that reaches back 150,000 years warns that this lifeline could become a threat. As the global climate warms and ocean systems shift, the monsoon is likely to intensify—bringing more floods to Australia and worsening droughts in East Asia.
Digging into the past
Led by Professor Michael Bird of James Cook University, and involving researchers from Flinders University, the study analysed sediment cores from Girraween Lagoon near Darwin. These layers contain ancient tree pollen and other clues revealing rainfall patterns over millennia. The findings, published in Quaternary Science Reviews, paint a detailed picture of how monsoon behaviour has changed—and what we might expect in the future.
“This is the longest continuous terrestrial climate record from the southern end of the Indo-Australian monsoon system,” Professor Bird said. “It delivers vital rainfall to millions across the Southern Hemisphere—and our data shows that its activity is closely tied to sea levels and ocean circulation, with serious implications for both hemispheres.”
Shifting shorelines and shifting rainfall
The research shows a clear link between changes in sea level and shifts in rainfall. As sea levels rise and fall over thousands of years, the northern Australian coastline has moved by as much as 320 kilometres. When the coastline is closer to the landmass, rainfall increases. When it retreats, parts of East Asia tend to suffer prolonged drought.
Monsoon bursts and melting ice
What’s more, the team discovered short-lived but intense periods of monsoon activity, some lasting less than 10,000 years. These wet spells lined up with so-called Heinrich events—abrupt bursts of freshwater from melting glaciers that disrupt the Gulf Stream in the North Atlantic.
“The connection surprised us,” Professor Bird said. “These distant pulses of freshwater into the North Atlantic appear to influence rainfall thousands of kilometres away in Australia. The mechanism involves the weakening of the Gulf Stream, which has knock-on effects for atmospheric circulation across the globe.”
A warning from the past
And that’s where the modern warning comes in. Scientists already know the Gulf Stream is weakening due to ongoing climate change—and this study suggests that if that continues, it could intensify rainfall in Australia’s north and worsen drought conditions in parts of East Asia.
“This isn’t just ancient history—it’s a window into what’s starting to happen now,” said study co-author Professor Corey Bradshaw, a global ecologist at Flinders University. “We’re seeing drying trends in East Asia and wetter conditions in north-western Australia, particularly since the 1950s. Our data suggest this could be just the beginning.”
Global ripple effects
The implications are significant. The Indo-Australian monsoon system spans a vast area—from China through Southeast Asia, across the equator, and down into northern Australia. It affects nearly a billion people and crosses five major biodiversity hotspots.
“Putting this in context,” Bradshaw said, “we’re talking about impacts on food systems, infrastructure, water supply, and ecosystems across a region that includes some of the world’s most densely populated and ecologically sensitive zones.”
Why this study matters now
The study is one of the most comprehensive attempts to piece together long-term climate trends in the Southern Hemisphere’s monsoon belt. Until now, much of the global monsoon research has focused on the Northern Hemisphere. But as this work shows, changes in one half of the globe often trigger ripple effects across the other.
With Australia already facing the consequences of a changing climate—including more frequent extreme weather events and rising sea levels—this kind of research is crucial.
“Understanding the monsoon’s past is vital for predicting its future,” said Bird. “The more we know, the better we can prepare for what’s coming.”
If you enjoyed this feature, you might like our story on killer whales!