A weathered stone house with a rusted metal roof stands abandoned in a dry, barren landscape under a clear blue sky. The structure has two chimneys, three empty window openings, and an open front door revealing the desolate terrain beyond. To the right, a cylindrical metal water tank sits on the parched ground, surrounded by sparse dry grass and patches of exposed soil. The scene evokes isolation and decay amid a vast, arid expanse.

Reconstructing 1,000 years of El Niño and La Niña to better understand our future

The El Niño-Southern Oscillation (ENSO) is the world’s largest source of climate variability. In Australia, it’s contributed to devastating floods and gruelling droughts in recent years.

Our understanding of ENSO is limited to recent memory and modern records. Those over the age of 50 might recall the powerful 1982-83 El Niño event, while older generations may remember the other significant El Niño in 1957-58. 

These events, though rare, can leave very impactful and even traumatic memories for those who experience them.The scarcity and profound impact of these El Niño events makes it crucial to understand them better. 

But you’ll struggle to find anyone who knows what ENSO was doing in 1791, unless you happen to visit the ARC Centre of Excellence for 21st Century Weather.

Research led by Dr Mandy Freund of the University of Melbourne has expanded our understanding of ENSO beyond the modern record of observed temperature and rainfall.

Conducted by a team also based at the University of Tasmania, the University of Newcastle and Australia’s national science agency, CSIRO, the review shows that our understanding of ENSO – based on modern data – doesn’t tell the full story about this complex, impactful phenomenon. 

Published in the journal Wiley Interdisciplinary Reviews: Climate Change, the work indicates that ENSO activity over the last 150 to 200 years may have been particularly varied and active, relative to other centuries. 

However, that doesn’t mean we should expect calm or predictable activity in the years or decades ahead, because the influence of significant average global temperature increases, caused by human carbon emissions, on ENSO are yet to be understood. 

To learn how ENSO behaved before modern times, researchers turned to two broad sources of evidence – the documentary evidence from human history, and natural archives.

Long before thermometers and rainfall gauges, people were already writing down the impacts of unusual climate swings, even if they didn’t know the causes or have a name for them. 

These historical documents describe prolonged droughts and floods, failed harvests, river levels rising and falling far outside the usual range, and mass death of marine life.

Early ship logs, missionary reports, colonial records and river height measurements were combined to infer when El Niño and La Niña events were likely to have occurred.

Some of the first reconstructions even extended back to the 7th century, drawing on Nile River flood records. Later studies refined and corrected these chronologies, combining written records with physical evidence from natural archives to build more reliable timelines of past El Niño and La Niña events.

Alongside historical documents, scientists now rely heavily on what are often called natural climate archives. These include tree rings, corals, cave deposits, ice cores and lake and marine sediments.

Each of these sources stores chemical or physical traces of past temperature, rainfall and ocean conditions. Read carefully, they allow researchers to reconstruct climate variability year by year.

Some of these natural records extend back to around 900 CE. Together, they help to create a picture of El Niño behaviour over many centuries.

When scientists compare these long reconstructions, they gain a multifaceted view of past ENSO behaviour. These reconstructions, derived from various archives, proxies, methods and geographical locations, offer both shared and complementary information.  

Several records show that the 19th century sits within a period of elevated ENSO variability. In plain terms, the climate system appears to have been more restless than usual.

That does not mean droughts and floods were unknown in earlier centuries. But it does suggest that the baseline used to define “typical” Australian climate risk may have been set during a naturally volatile phase.

This matters because water systems, farming practices and planning rules that were designed around that baseline may not perform in the same way if El Niño enters a quieter or differently structured phase, or if warming caused by human activity reshapes how ENSO operates altogether.