A prehistoric lake discovered in South Australia has highlighted the threat that humanity faces from sea level rise.
University of Newcastle researcher Hannah Power was part of a team that made the discovery.
The team revealed that a 240-kilometre long lake existed in the Murray-Darling basin when sea levels were about two metres higher.
The scientists extracted 30 metres of sediment cores deposited in the ancient lake 5000 to 8000 years ago.
They pieced together the climate history of the basin, providing fresh insight into future sea level rise scenarios as the globe heats up.
"The key thing that caused the lake to form was the fact that sea level was two metres higher than it is today," Dr Power said.
"The findings are really important because we've discovered a previously unknown record of our climate history for our most economically and politically significant river basin."
She said Australia had responded swiftly to COVID-19, but "we're not doing enough to respond to climate change".
"We need to take action now, it needs to be sustained and significant. The fact the sea level is rising is clear cut in the scientific community."
Even if carbon dioxide and greenhouse gas emissions were eliminated now, "we'd probably still see sea level rise happening to about 2100, potentially even beyond".
"Sea levels might be two metres higher by 2100 - that's not out of the question. How much sea level rise we will see in our lifetime entirely depends on what we do."
Humanity must make radical changes to the way it runs societies and generates energy to "limit sea level rise to something that we might be able to manage in places".
"If we continue with business as usual, we will experience really significant sea level rise that will have really significant impacts all around the world."
As for the prehistoric lake, computer modelling was used to demonstrate that it existed. The team then collected physical evidence through extracting the cores.
"We've discovered in the cores that we have 11 metres worth of lake sediment that accumulated at a rate of about three millimetres of sediment per year," Dr Power said.
"What we hypothesise at this stage is each layer of sediment represents an annual cycle with things like the snow melt from the Australian alps every spring. Some will represent big floods in the Murray or Darling or both river systems.
"We've discovered this record - now we need to find out what the record tells us."
Dr Power's colleague - University of Sydney Associate Professor Thomas Hubble - had been previously examining why the riverbanks were collapsing in the Lower Murray River during the Millennium drought.
"As part of that, he was looking at the sediments that comprised the river banks and floor of the river. He looked at the sediments and thought, 'These don't look like what we could expect to see at the end of a massive river system. They look like lake sediments'."
As sea levels decreased over the last 5000 years, the lake slowly drained and became a river again.
PhD student Dr Anna Helfensdorfer said the Lower Murray River was "very different from most other modern rivers".
They typically had channels that deposit sediments "rather than channels that cut away into layers of previously deposited material".
-
Hunter petrol cheapest in 15 years as prices plummet below 90c/l
-
'Incredibly strong potential': Hunter company's ventilator on state goverment shortlist
-
'This time will pass': Mental health experts urge people to seek help if distressed
-
Australia-New Zealand bubble hopes growing
- Hunter schools exceed new enrolment caps
