Antarctic ice core research holds lessons on drought patterns in south-west Western Australia

Ancient ice cores, drilled from Antarctic glaciers more than 6,000 kilometers from Western Australia, are the unlikely guardians of a glimpse of the climate drying up in the state’s southwest .

Perth ended June with less than half the average monthly rainfall in what was a dry start to winter in the southwestern corner of the state.

It’s a familiar scenario for the region, which is in the midst of a 50-year drying trend, considered one of the worst in the world, due to climate change.

But as scientists try to disentangle human-caused impacts from natural variability, one of the biggest challenges has been the short 140-year span of climate records kept by the Bureau of Meteorology.

An ancient ice core and a chance “teleconnection” between Antarctica and the Southwest has now given scientists insight into the region’s 2,000-year drought history.

The Southwest is bucking the national forecast for wet weather this winter.(ABC: Robert Koenigluck)

Three mega droughts in the past two millennia

According to Antarctic climatologist Tas van Ommen of the Australian Antarctic Division, the analysis showed that the South West had only experienced a comparable drought twice in the past two millennia.

Dr van Ommen said this happened around AD 400 and then again in AD 750.

He said he was able to come to this conclusion thanks to a “teleconnection” between Antarctica and the South West recognized in 2010 using a 750-year-old ice core.

He said they found that when snowfall increased in Antarctica, precipitation decreased in the region.

Glaciologist Dr. Tas van Ommen
Dr. Tas van Ommen studies ice cores in an effort to provide detailed climate reconstructions.(ABC News: Jane Norman)

“As we looked at the atmospheric patterns that were actually bringing this moisture and snowfall to Antarctica, we could start to see that in this pattern there was also a signature of cold, dry air coming into Western Australia.” , did he declare.

The latest research, led by PhD student Yaowen Zheng, extended Dr van Ommen’s earlier work by reconstructing Antarctic snowfall using a longer 2,037-year-old ice core from the same region.

Thanks to this, they were able to draw conclusions about the past climate of South West WA for the same period.

The ice core research is the longest reconstruction of past precipitation variability in the region to date, other than long-term modelling.

Glaciologist Dr. Tas van Ommen
Glaciologist Tas van Ommen demonstrating the process of ice coring.(ABC News: Jane Norman)

The research was accepted by peer review, but some caution was noted as the evidence assumes the link between snow at Law Dome and rainfall in south-west Western Australia remains strong over time. time, which may not have been the case in past centuries.

Long-term “unusual” drought

Dr van Ommen said ice core research showed the time between previous drying events meant the current drought was highly unusual.

Close up of hands holding cylinder shaped piece of ice cream
Ice cores can help verify if climate modeling is working.( ABC News: Owain Stia-James)

But he said just because it had happened before didn’t mean human influence hadn’t played a role.

Dr van Ommen said their records showed the current increase in snowfall in Antarctica was “slightly more extreme” than the last two events.

He said they were also able to use the ice core as a “verification” for their climate models.

He said the models matched fairly well what the ice core indicated as periods of increased snowfall and decreased precipitation in the past, but could not produce the current drought as long as the increase in carbon dioxide was not added.

“And so everything matches everything else and we have more confidence in what the model is telling us,” he said.

Dr Tas van Ommen stands next to an ice core at the Law Dome Ice Core Drill Camp, Antarctica.
Dr. Tas van Ommen stands next to an ice core at the Law Dome Ice Core Drill Camp.(© J Pedro/Australian Antarctic Division)

Cautious conclusions about the past

Other methods have been used to study the past climate in the region, including a 2021 Tree Ring Study, which examined the climate for the past 668 years in the Wheatbelt region of WA.

Similar to research on ice cores, research on tree rings has revealed that it is likely that natural climate variability and human-caused climate change have contributed to the recent decline in rainfall.

But unlike the ice-core research, the tree-ring study found the Wheatbelt had suffered five droughts since 1350.

A tree ring
The wider the ring, the more water the tree has taken up in a given year, giving insight into the past climate of an area.(Supplied, Unsplash: Joel and Jasmine Forestbird)

Dr van Ommen said the differing results were likely related to the geographic areas in the South West that each search focused on.

“The ice core record is more applicable for the Perth catchment and the high rainfall western wheat belt, while the Callitris (tree) is more applicable for the drier interior eastern zone,” said he declared.

Nonetheless, he said their evidence on ice cores remains open to continued scrutiny.

Climate history is the key to sound research

Dr van Ommen said understanding past climate was not just a step back in history, but a way to make climate models more robust.

“Part of that is testing the models with longer-term records of past climate,” he said.

“So that’s really the key is to better predict what’s going to happen.

“There is also another strand, and that is that we need to understand what might happen if our current understanding is inadequate – this is where past evidence of how the climate has changed is key.”

The oldest ice core is 800,000 years old, but Dr van Ommen said his aim was to understand even more from longer records.