Climate Clues: The mystery behind Moana: Why Polynesians suddenly sailed east

David Sear, Manoj Joshi & Mark Peaple

NEW DELHI: The same question drives both the plot of Disney’s Moana and decades of archaeological research: why, after centuries of relative stability, did Polynesian voyagers suddenly begin settling islands thousands of kilometres away across the Pacific?

While the Moana films are fictional, they draw inspiration from a real-world maritime marvel. New climate evidence may finally explain why these ancient navigators embarked on their epic voyages.

The backdrop to this history is the "long pause." Around 3,000 years ago, the Lapita people — ancestors of the Polynesians — sailed east into the Pacific, settling Samoa and Tonga. They brought distinct pottery styles and established a thriving island-based culture.

Yet, for the next 1,700 years, eastward exploration ground to a halt. During this time, populations in Tonga and Samoa grew and developed their own distinct post-Lapita cultures.

Then, between 900 and 1100 AD, ancestral Polynesians suddenly undertook a massive phase of eastward migration. Over just a few centuries, voyagers in massive, double-hulled sailing canoes reached Hawai’i, Aotearoa (New Zealand), and Rapa Nui (Easter Island). The presence of sweet potatoes across the region indicates they likely even made contact with the continental Americas.

When European navigators arrived centuries later, they were astonished to find isolated atolls peopled by communities sharing deep cultural and linguistic roots.

For generations, anthropologists have debated what ended the long pause. Was it new sailing technology designed to combat easterly trade winds? Was it driven by social pressures? Or was there an environmental catalyst?

Ultimately, island survival hinges on a single critical resource: rainfall. While ancestral Polynesians were highly adaptable, prolonged droughts during periods of high population density would mean an island could no longer support its people.

Until recently, scientists lacked climate evidence from the Tonga and Samoa region during this critical migration era. However, our team was able to reconstruct past climate shifts by analysing hydrogen isotopes preserved in ancient lake and swamp sediment.

In the tropics, the isotopic composition of rainwater reflects rainfall amounts. As algae and plants grow, they lock this chemical signature into molecules that survive in mud for thousands of years.

Using this technique, we found evidence of a severe, sustained dry period in the southwest tropical Pacific between 850 and 1200 AD. Our results, published in the Journal of Pacific Archaeology, indicate this was the driest period the region had experienced in 2,000 years. Crucially, this drought coincided with peak island populations.

This shift was likely driven by the South Pacific Convergence Zone (SPCZ), a major rain belt that moves based on sea surface temperatures. This matches genetic data showing Samoa’s population surged around 1000 AD.

It appears a perfect storm of factors aligned: severe climate stress, expanding populations, and evolving canoe technology. Faced with drying homelands, these extraordinary navigators responded with ingenuity and resilience, launching a new era of oceanic exploration.