01/09/2021

(AU The Conversation) 1,600 Years Ago, Climate Change Hit The Australian Alps. We Studied Ancient Lake Mud To Learn What Happened

The Conversation -  |  | 

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If you’ve ever visited Australia’s highest peak — Mount Kosciuszko — you might remember the long uphill trek to the summit past some of Australia’s most picturesque and rugged landscapes.

Vibrant snow gums, boardwalks with meadows of exquisite alpine plants, and blinding patches of snow.

As you approach the summit, a quartet of stunning blue lakes appear, created by glaciers during the last ice age that carved new valleys out of the mountain.

Lakes like these are windows to the past, offering an opportunity to understand how our climate and environment has changed over hundreds to thousands of years. One such lake, Club Lake — so-named for its resemblance to a suit in a deck of cards — was the focus of our new study.

After studying the lake’s sediment, we learned the Australian Alps experienced a sudden climate change about 1,600 years ago that brought a long spell of warmer conditions. What makes this sudden warming event particularly interesting is that it bears striking similarity to today.

Climate change in the Australian Alps

The Australian alpine region is the traditional home of a number of Aboriginal groups, including the Ngarigo, Walgalu and Djilamatang people. It is also home to highly diverse flora and fauna that occur nowhere else, from billy buttons (Craspedia costiniana) known for their vibrant yellow rosette of tiny flowers, to the broad-toothed rat and its chubby cheeks.

Mountain pygmy possums like in Australia’s alpine region, and are under dire threat from climate change. AAP Image/Department of Sustainability and Environment/Tim Arch
But this unique wildlife is under immense threat from climate change.

By 2100, Australia may warm by at least 4℃, with bushfires becoming more frequent and devastating. The fragile alpine ecosystem will be hit particularly hard by these changes.

Many of Australia’s alpine species are already near their climatic limits, and are constrained by altitude. They’re at risk of becoming regionally extinct if their climatic thresholds are exceeded.

As the temperature warms, treelines move upslope to cooler temperatures, pushing alpine flora and fauna to higher elevations. At some point they can go no higher — they’re squeezed out of their niche.

The critically endangered mountain pygmy-possum, for example, relies on the seasonal snowpack for winter hibernation, but increased temperatures are limiting this habitat.

A dip into the past

Our study showed Club Lake holds vital clues to the link between rising temperatures, loss of native plant species and more frequent fires in the Snowy Mountains.

Lake sediments are used all over the world as indicators of climate and environmental change because of the unique way they trap material. A body of water can act as a seal that ensures sediments are largely undisturbed over time.

We extracted sediments from the bottom of Club Lake to a depth of 35 centimetres. This equates to about 3,500 years of history, approximately 100 years for each centimetre.

Club Lake in Mt Kosciuszko. Shutterstock
To work out how temperatures have changed over this time, we looked for the presence of molecular fossils, called “lipid biomarkers”. Analysing these biomarkers in the laboratory can tell us what the temperature in the environment was like, hundreds or thousands of years ago.

In the 3,500 years we examined, we detected a gradual warming trend. Superimposed on this, we found a sudden warming event that started 1,600 years ago, and lasted about six centuries. We suspect it was due to an atmospheric phenomenon linking higher tropical sea surface temperatures to southeastern Australia.

We’re not yet sure how much of Australia was affected by this warming, but other research from 2018 measured similar temperature changes in stalagmites from the Yarrangobilly caves 50 kilometres away.

Alpine snow gums (Eucalyptus pauciflora). Zoë Thomas
What happened during this climate change?

During this unusual warmth, alpine herbs and shrubs declined, while the abundance of trees, particularly eucalyptus, increased. We know this by looking at grains of pollen preserved at different depths within the lake sediment samples, which indicates what types of plants were growing nearby.

We also found small particles of charcoal, produced by bushfires, embedded within the sediment layers. This showed the changes in vegetation also coincided with greater fire activity.

What surprised us most, however, was discovering a large increase in mercury at this time.

Mercury, which occurs naturally in the environment, is the only metal that’s liquid at room temperature, and is particularly sensitive to temperature changes. Higher temperatures enhance mercury deposition from the atmosphere, and our study shows a five-fold increase in mercury flux 1,600 years ago.

Alpine herbfields. Nicola Pain
Industrial activities over the last 150 years, such as burning coal, have increased the abundance of mercury significantly. Our findings suggest future climate change is likely to increase the risk of mercury exposure not just in cities, but also in the seemingly remote Australian alpine environment.

Mercury contamination is a significant public health and environmental problem. At certain levels it’s poisonous to the nervous system, and it does not easily degrade.

What can we do?

Insights from the past can help governments, environmental agencies, and scientists come up with effective strategies to protect the vulnerable flora and fauna of the Australian Alps. But it’s not just changes in climate they’ll have to contend with in future.

There are other perils, such as soil erosion and habitat fragmentation from the legacy of sheep and cattle grazing, and tourism. Invasive pests and pathogens are likely to further reduce the resilience of these alpine ecosystems.

Feral horses are a significant threat to native wildlife in Australia’s alpine region. Shutterstock
Restoration programs over the last 50 years have aimed to revitalise the natural vegetation in the Kosciuszko National Park following 135 years of grazing — finally banned in 1969 — and the environmental damage caused by the Snowy River Hydro-Electric scheme.

More recently, the federal government has committed A$3.5 million towards recovery from the devastating 2019-2020 bushfires. Incorporating Aboriginal knowledge into mainstream fire management is essential for tackling future crises.

This is the critical time for climate action to protect this unique and iconic Australian landscape.

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(Book Review: Nature) Witness In US Climate-Change Law Suit Tells All

Nature - Catherine Higham

Was the government a primary cause of the US addiction to fossil fuel? An expert who testified gives evidence.
Young people rally outside the US Supreme Court in 2018 to support the climate case Juliana et al. v. US government. Credit: Win McNamee/Getty

MIT Press (2021)
The week of 24 May 2021 was, in the words of one leading litigator, “a great week to be a climate lawyer”. Two landmark judgments sent shock waves through the legal world.

On 26 May, the Hague District Court ordered Royal Dutch Shell to reduce its greenhouse-gas emissions by 45% from 2019 levels by 2030.

It was the first time that a court had ordered a company to take such action on the basis of harm to others.

The next day, an Australian judge found that the minister of the environment had a duty of care to Australian children to protect them from foreseeable future harms caused by increased greenhouse-gas emissions in the atmosphere.

Both judgments represent years of graft by committed plaintiffs and legal teams.

They are also part of a wider story.

Around the world, some 1,850 ‘climate-change cases’ have now been filed, many by climate lawyers and clients who have turned to the courts to address the climate crisis by filling the gaps left by slow or inadequate government action.

Successes such as those in Australia and the Netherlands, unimaginable a decade ago, represent hard-fought victories in a continuing battle over the evolving understanding of rights and responsibilities in the context of a changing climate.

Neither would have been possible without previous cases — won or lost — that introduced climate science into the courtroom.


It is against this backdrop that Gus Speth’s timely book must be understood.

It began as an expert report in a famous climate-change case: Juliana et al. v. US Government, submitted to the Oregon District Court by 21 youth plaintiffs and others in 2015.

The claimants’ arguments rested on the federal government’s constitutional obligations to protect US citizens’ rights to life, liberty and property, and to protect the atmosphere as part of a “public trust”.

They alleged that the government had violated these duties by “perpetuating” a fossil-fuel-based energy system, despite “long-standing knowledge” of its harms.

In their introduction to the book, Julia Olson and Philip Gregory, counsel for the plaintiffs, explain that they had to demonstrate that the government had both allowed and knowingly created the alleged harms.

This required them to prove that the conduct of the federal government was a primary cause of the US addiction to fossil fuels, the point Speth’s report was commissioned to demonstrate.

Speth was an inspired choice of witness.

Drawing on first-hand knowledge from his time as chair of the US Council on Environmental Quality during the administration of president Jimmy Carter (1977–81), and his founding role in several major environmental non-governmental organizations, Speth gives a clear and concise account of the scientific evidence available to successive US presidents and Congresses over five decades.

He provides a chilling description of the gulf between the safer course of action recommended by scientists and advisers, and the reality of federal policy.

Given the book’s original purpose — an exhaustive presentation of evidence — at times it can seem like a laundry list of warnings ignored.

Fortunately, Speth peppers it with gripping insider details.


One compelling example: the speed with which the administration of George H. W. Bush (1989–93) turned away from early recognition of the benefits of using policy to reduce climate risk, and became dominated by staffers who used material from the fossil-fuel industry to cast doubt on the science.

The administration of Bill Clinton (1993–2001) ran a miscalculated public-awareness campaign that actually increased the partisan divide in perceptions of climate science.

These episodes offer fascinating insight into subsequent events.

Much of the story is not new. Elements of the interactions between the US fossil-fuel industry and the federal government have been charted elsewhere, such as in the work of science historian Naomi Oreskes, or in climate scientist Michael Mann’s book The New Climate War (2021).

Yet even for the familiar reader, Speth’s focus on the federal government provides a fresh perspective.

A key feature of the Australian and Dutch cases is that, unlike many before them, they establish a legal responsibility for the defendants to act now and in the future.

The important issue was not what the minister or Shell knew in the past, but what they should do now, in the light of the global consensus on the climate threat.

Although establishing the parameters for future decisions is a crucial goal of climate litigation, Speth’s book reminds us that major questions about historic responsibility cannot be ignored.

In the US context, the Juliana plaintiffs have begun settlement talks with the administration of President Joe Biden and vice-president Kamala Harris, which might lead to answers.

Around the world, similar reckonings with the past are just beginning.

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(AU SMH) Even 1.5C Warming Will Still Leave World’s Coasts Exposed To Extremes

Sydney Morning Herald - Peter Hannam

One-in-100-year extreme sea-level events along the world’s coastal regions will become annual occurrences by the end of the century even if the most ambitious climate change action is taken.

The findings, which include work by Australian researchers, are published on Tuesday in Nature Climate Change journal.

The paper builds on the Intergovernmental Panel on Climate Change’s latest report and sought to estimate what was the lowest amount of global warming that would trigger at least a 100-fold change in the frequency of the present-day once a century extreme event by 2100.

A man takes pictures of high waves along the shore of Lake Pontchartrain in Louisiana as Hurricane Ida nears. Climate change will lift sea levels everywhere, adding more heat to the oceans. Credit: AP
The research combined observations at 179 spots with climate modelling to assess more than 7200 locations around the world.

About half the world’s coastal areas will endure such extreme sea-level events “even under 1.5 degrees of warming, and often well before the end of the century”, the paper said.

“We combined different data sets across international research groups,” said Ebru Kirezci, an engineering post-doctoral student at the University of Melbourne and one of the paper’s authors.

“Governments and policymakers should do more work on protection and mitigation scenarios.”

For Australia, the areas likely to see the fastest rise of extreme sea-level events will be in the east and the south, but also areas of south-west Western Australia, Dr Kirezci said.

Such events lead to beach erosion, inundation of inland areas and other damage.

Even at 1.5°C warming, many regions will see extreme sea levels

Source: Nature Climate Change
According to the recent IPCC report, global sea levels have risen an average of about 20 centimetres between 1901 and 2018 as the warming oceans swell and more land-based ice melts into the sea.

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The average annual rate has accelerated from 1.3 millimetres in the first seven decades of the 20th century, to 1.9 millimetres in the following 25 years to 3.7 millimetres between 2006 and 2018, the IPCC stated.

The paper found areas with relatively narrow sea-level changes now, such as in parts of the tropics that are not subject to big cyclones and the Mediterranean, will register the shift to more extremes sooner.

By contrast, some northern hemisphere coastlines will see little change even at 5 degrees of warming.

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John Church, a former senior CSIRO sea-level researcher now working at the University of NSW, said the paper contained “new and useful information”.

Even at 1.5 degrees, the lower end of the Paris Agreement, “we’re going to have to adapt”, Dr Church said. “It’s an important message to get out.”

Dr Church’s past work showed that in the 20th century, the risk of extreme events along the west and east coasts of Australia had roughly tripled.

“I’d guess since 2000 they have increased by another factor of three,” he said.

Global warming
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Dr Kirezci said governments needed to prepare for the inevitable sea-level rises by considering sea walls and other barriers.

Governments should also assess which coastal communities are most at risk and consider relocating them inland, and also investigate early warning systems to improve safety.

Her next line of work has been to examine the socio-economic damage likely for populations in every country.

Sea-level increases vary around the world because of two main processes, Dr Church said.

One is a change in mass distribution, such as in Greenland where the land actually rises as its heavy ice sheets melt.

Changes in currents, such as the strengthening of the East Australian Current, also contribute to difference rates of sea-level rises, he said.

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