How did a changing climate in the tropical South Pacific contribute to the eastward migration and settlement of Polynesia?

The migration of humans into the eastern Pacific was relatively rapid and focused around 900-1250 CE. Although the causes for this migration are varied, we put forward evidence to suggest that a change in the mean state of the tropical South Pacific from La Niña like to El Niño like conditions accompanied by an increase in climate “shocks” around the period of migration, could have created conditions to promote migration east into the Pacific. We use a range of sediment archives and hydroclimate proxies located in sites within the region of migration, to reconstruct climate conditions in the ‘sending’ islands, and ‘receiving’ archipelagos. Climate in the period immediately prior to the eastward migration was characterised by a drier southwest Pacific. During the period following settlement of the central region of eastern Polynesia, the mean climate state in receiving islands became wetter, with fewer climate “shocks”. Results from socio-hydrological models highlight the sensitivity of growing populations to droughts within a drying climate. Using these lines of evidence, we suggest that as populations grew, particularly in drought-sensitive islands, people with some knowledge of eastern “Gateway islands”, chose to move east, fortuitously at a time when wetter conditions supported their long-term settlement.