Australasian Science: Australia's authority on science since 1938

Reaching Australia’s Ancient Refugia

painted rock shelters

Australia’s first peoples have painted rock shelters like these for at least 35,000 years, though this activity was discontinued during the stresses of the LGM. Photo: P.S.C. Taçon with permission of Ronald Lamilami and the Aboriginal people of the Namunidjbuk Estate, Wellington Range, Arnhem Land.

By Michelle Langley

New research reveals how Australia’s ancient Aboriginal populations were challenged by extreme climate change between 23,000 and 12,000 years ago, and provides insights into how people may respond to dramatic climate change in the future.

The adventurous seafarers who first reached the northern shore of Sahul – the Pleistocene low sea-level landmass of New Guinea and Australia – were certainly some of humankind’s early high achievers. However, reaching this vast southern continent was not the last great challenge to be met by Australia’s first people.

Having navigated the dangers of the open sea, these first Australians were faced with an enormous landmass never before inhabited by humankind, but home to a range of unique and never-before-seen flora and fauna including rhinoceros-sized wombats, marsupial lions and giant goannas known as Megalania that weighed more than 150 kg and perhaps as much as 330 kg.

Over the next 25,000 years, humans successfully explored and exploited the entire continent. Each of the vastly different environments – from tropical coastlines to the desert heart to the alpine areas of the south-east – were penetrated and its resources extracted for food or to manufacture a wide range of tools needed for day-to-day life.

However, by around 23,000 years ago the climate, and consequently the physical environment, began to change. It became considerably cooler and much more arid. Mean annual temperatures decreased by about 10°C compared with the present, while mean annual rainfall declined by approximately 60%. Vegetation changed to more steppe-like and grassland-dominated environments, while the arid zone expanded out into what was the semi-arid zone. In short, the environment became harsher and far more challenging for the entire population of Sahul.

This period of global wide climate change, known as the Last Glacial Maximum (LGM), provided the second great challenge of the first Australians. Recent research undertaken by an international team of researchers and published in the Journal of Archaeological Science has provided new insights into the impact that extreme climate change had on Sahul’s prehistoric populations. These new insights were obtained from the analysis of a huge dataset of radiocarbon data – around 5500 dates in total – collected from every archaeological site (in the studied time range) identified so far in Australia. Radiocarbon data was used in this study as every time an archaeologist gets a date for a site it is usually taken from a cooking pit, a burial, a midden, or some other vestige of human activity that indicates the presence of people in the ancient landscape.

Changes in Territory

Having spread throughout the continent between the time of their first landfall and the beginning of the LGM, Australia’s first peoples accessed a great range and abundance of plant and animal resources. With the changing climate, however, these resources – including water – became increasingly scarce, requiring whole regions to be abandoned in favour of “refugia”.

These refugia were areas that were well-watered – namely, major river systems and uplands with glaciers. As such, they provided not only freshwater, but also edible plants and animals.

Yet, the refugia were few in number and much smaller in size than the area previously available for occupation, and thus the resources they contained were limited. Even in these refugia, then, life wasn’t easy and a substantial decrease in the human population of Australia at this time is reasonably well-supported.

Refugia that appear to have been particularly important for human survival during the LGM include the Murray-Darling Depression, the Gulf Plains/Einasleigh Uplands, and the Tasmanian Central Highlands (see map). A number of additional refugia that were used less consistently also contributed to human survival in times of environmental hardship. These latter refugia include the Sydney Basin, the Central and Northern Kimberley, the Arnhem Plateau and the MacDonnell Ranges.

While human groups suffered great losses in population density and endured great resource and social stress throughout the LGM, this was not the only climate change event to effect Sahul and its human population. Only 4000 years after the end of the LGM, and after human groups had dispersed from the refugia and spread back out through the entire continent, the climate once again began to deteriorate. This second climate event, which occurred between 14,500 and 12,500 years ago, is termed the Antarctic Cold Reversal (ACR). While apparently not as severe as the LGM event, conditions became harsh enough that Australian populations were once again forced to move back into the refugia that had allowed them to survive previously.

Changes in Social Organisation

The environmental changes associated with the LGM and ACR required more from Sahul’s populations than abandoning large tracts of land for the relative safety of the few refugia.

Recent continental population models suggest that around 20,000 people occupied the continent during the earliest period of Sahul’s prehistory. Current archaeological evidence indicates that, prior to the LGM, people practiced highly mobile foraging and social strategies where groups travelled around the landscape from day-to-day acquiring resources and visiting neighbouring groups. As a result of the changing environmental conditions, however, they were required to become more restrained in their movements and give up their longstanding way of life.

Furthermore, not only did they have to abandon the way of life that had served them so well for the first 25,000 years of Australian prehistory, they also had to abandon their homelands and come together with various other groups in a restricted space with limited resources. This would have created an extremely stressful situation for all involved. In response to this stress, those groups who made it to the refugia may have chosen either to be competitive with one another for the limited resources available or to focus on wider social similarities that would enable a larger population to survive. Which of these scenarios occurred in each refugia is currently unknown.

These changes in social organisation are indicated by a decrease and even abandonment of particular forms of material culture – such as body ornamentation, small portable art pieces and rock art during the LGM. What changes in social interaction these patterns indicate exactly remains unknown.

In contrast, the social system that had been set up by those who survived the LGM appears to have been largely uninterrupted by the later ACR. Rather than abandoning the use of those artefacts that had been discontinued during the extreme conditions of the LGM, they appear to have been used in ever-increasing quantities across the continent. These time-intensive practices, including the production of rock art, ritual burials and the manufacture and transport of ornamentation (mostly made from marine shells that were attractive to early human societies globally) to be worn on the body became more and more frequent in the archaeological record of this period and the many thousands of years that followed.

Conclusion

While the first Australians were able to survive both the LGM and ACR climate change events, archaeologists have found that great changes and sacrifices were required of all those who inhabited the continent during these periods. Most peoples were forced to abandon their homelands for a period of some 10,000 years during the LGM and the later ACR, and retreat to spatially restricted refugia – the only places where freshwater and food remained available. Once there, they had to share the limited resources with others who were also striving to continue their existence as best they could while under extreme social and environmental stress. This stress is best represented by the substantial decrease in Sahul’s human populations during this period.

Clearly, humans in the past were just as vulnerable to the changing climatic conditions and environments as every other species who inhabited this continent. Despite having great adaptational flexibility and innovativeness – skills that enabled them to reach and colonise the continent early in the modern human story – they were still forced to abandon their lifestyles, homes and potentially parts of their cultural traditions for thousands of years in order to survive.

These events in Australia’s deep past allow insights into how Australia’s modern populations might respond to extreme climate and environmental change in the future. But we must remember that Australia is now home to far more people than the 20,000 estimated for the continent’s earliest inhabitants. Consequently, the refugia that served our ancient people so well in the past will not be able to sustain us in future climate change events.

Michelle C. Langley is a recent PhD graduate of the University of Oxford, and is currently undertaking postdoctoral research at the Australian National University.