Landscapes that have escaped fire for decades or centuries tend to harbour vital structures for wildlife, such as tree hollows and large logs. But these “long unburnt” habitats can be eliminated by a single blaze.

The pattern of fire most commonly experienced within an ecosystem is known as the fire regime. This includes aspects such as fire frequency, season, intensity, size and shape.

Fire regimes are changing across the globe, stoked by climate and land-use change. Recent megafires in Australia, Brazil, Canada and United States epitomise the dire consequences of shifting fire regimes for humanity and biodiversity alike.

We wanted to find out how Australian fire regimes are changing and what this means for biodiversity.

In our new research, we analysed the past four decades of fires across southern Australia. We found fires are becoming more frequent in many of the areas most crucial for protecting threatened wildlife. Long unburnt habitat is disappearing faster than ever.

Uncovering long-term changes

“Fire regimes that cause declines in biodiversity” was recently listed as a key threatening process under Australia’s environmental protection legislation.

However, evidence of how fire regimes are shifting within both threatened species’ ranges and protected areas is scarce, particularly at the national scale and over long periods.

To address this gap, we compiled maps of bushfires and prescribed burns in southern Australia from 1980 to 2021.

We studied how fire activity has changed across 415 Australian conservation reserves and state forests (‘reserves’ hereafter), a total of 21.5 million hectares. We also studied fire activity within the ranges of 129 fire-threatened species, spanning birds, mammals, reptiles, frogs and invertebrates.

We focused on New South Wales, the Australia Capital Territory, Victoria, South Australia and Western Australia because these states and territories have the most complete fire records.

More fire putting wildlife at risk

We found areas of long unburnt vegetation (30 years or more without fire) are shrinking. Meanwhile, areas of recently burnt vegetation (5 years or less since the most recent fire) are growing. And fires are burning more frequently.

On average, the percentage of long unburnt vegetation within reserves declined from 61% to 36% over the four decades we studied. We estimate the total area of long unburnt vegetation decreased by about 52,000 square kilometres, from about 132,000 sq km in 1980 to about 80,000 sq km in 2021. That’s an area almost as large as Tasmania.

At the same time, the mean amount of recently burnt vegetation increased from 20% to 35%. Going from about 42,000 sq km to about 64,000 sq km in total, which is an increase of 22,000 square kilometres.

And the average number of times a reserve burnt within 20 years increased by almost a third.

While the extent of unburnt vegetation has been declining since 1980, increases in fire frequency and the extent of recently burnt vegetation were mainly driven by the record-breaking 2019–20 fire season.

Which areas have seen the biggest changes?

The strongest increases in fire frequency and losses of long unburnt habitat occurred within reserves at high elevation with lots of dry vegetation. This pattern was most prominent in southeastern Australia, including the Kosciuszko and Alpine national parks.

In these locations, dry years with low rainfall can make abundant vegetation more flammable. These conditions contribute to high fire risk across very large areas, as observed in the 2019–20 fire season.

Threatened species living at high elevations, such as the spotted tree frog, the mountain skink and the mountain pygmy possum, have experienced some of the biggest losses of long unburnt habitat and largest increases in fire frequency.

Multiple fires in the same region can be particularly problematic for some fire-threatened animals as they prevent the recovery of important habitats like logs, hollows and deep leaf-litter beds. Frequent fire can even turn a tall forest into shrubland.

What does this mean for Australia’s wildlife?

Fire management must adapt to stabilise fire regimes across southern Australia and alleviate pressure on Australia’s wildlife.

Indigenous land management, including cultural burning, is one approach that holds promise in reducing the incidence of large fires while providing fire for those species that need it.

Strategic fire management within and around the ranges of fire-threatened species may also help prevent large bushfires burning extensive portions of species’ ranges within a single fire season.

We can also help wildlife become more resilient to shifting fire regimes by reducing other pressures such as invasive predators.

However, our efforts will be continually undermined if we persist in modifying our atmosphere by burning fossil fuels. This means conservation managers must also prepare for a future in which these trends continue, or hasten.

Our findings underscore the increased need for management strategies that conserve threatened species in an increasingly fiery future.

William Geary, Lecturer in Quantitative Ecology & Biodiversity Conservation, The University of Melbourne; Dale Nimmo, Professor in Ecology, Charles Sturt University; Julianna Santos, Research fellow in Ecology and Conservation Science, The University of Melbourne, and Kristina J Macdonald, PhD Candidate, Deakin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

It may come as a surprise to hear 2023 was Australia’s biggest bushfire season in more than a decade. Fires burned across an area eight times as big as the 2019–20 Black Summer bushfires that tore through 10 million hectares in southeast Australia.

My research shows the 2023 fires burned more than 84 million hectares of desert and savannah in northern Australia. This is larger than the whole of New South Wales, or more than three times the size of the United Kingdom. The scale of these fires is hard to comprehend.

The speed at which these fires spread was also incredible. In just a few weeks of September and October, more than 18 million hectares burned across the Barkly, Tanami and Great Sandy Deserts of the Northern Territory and Western Australia.

I presented this research into the 2023 fires at the International Fire Behaviour and Fuels Conference this month in Canberra. I described the scale of these fires, why they occurred, and how fires could be better managed to help protect remote but ecologically and culturally important regions of Australia.

Why did this happen?

Fire and rain are closely connected. Rain triggers grass growth. When it dries out, grass becomes fuel for fires.

For example, you can see the pattern of more fire following wet years repeating at periodic intervals over the past 20 years of fire in the Northern Territory.

In this way, La Niña is the major driver of these massive fires in the desert.

Although 2023 was a massive fire year, 2011 was even bigger. In the NT alone, more than 55 million hectares burned in 2011, compared with 43 million in 2023.

When fuel is dry and weather conditions are extreme, lightning strikes tend to start more fires across savannah and desert rangelands.

It has been variously suggested in the media and on social media that these fires are part of a “normal” cycle, a consequence of climate change, or largely the result of arson. Such simplifications fail to grasp the complexity and history of fire management in desert Country.

The main driver of these fires was the very large fuel loads. These wet growing seasons are part of the natural cycle. While climate change can make fire conditions more extreme, in this case it’s not the main cause. However, the scale of these fires was not “normal”.

How can fires be managed?

For many thousands of years, Indigenous people managed fuel loads across these vast landscapes.

The sophisticated use of fire in Australia’s highly flammable tropical savannas has been recognised as the world’s best wildfire management system.

Traces of this long history of traditional fire practice can be seen in aerial photos of desert Country from the 1940s. Research analysing these photos has shown extensive and complex “fuel mosaics” spread like patchwork quilts over vast parts of the WA deserts.

The term mosaic refers to having many patches of vegetation of different ages, some recently burnt with sparse cover, some long unburnt with old, large and connected spinnifex clumps and small trees.

This provides habitat for a broad range of animals, because different species prefer different amounts of ground cover. It also hinders the spread of fire because areas subject to more recent fire have insufficient fuel to carry new fires for many years.

Efforts have only just begun to bring good fire management back into these landscapes in a coordinated and large-scale way.

In 2022–23 Indigenous ranger groups conducted extensive burning operations. They travelled more than 58,000km by air and road, burning from cars, on foot and dropping incendiaries.

These burns were astoundingly effective. Even though large fires still ripped through these deserts in 2023, by mapping the fuel reduction fires and overlaying the spread of subsequent wildfires, we can see the 2023 fires were limited by previous burns.

For example, the fire spread animation below shows fires moving through a complex mosaic comprising fuel of different ages. One fire can be seen moving more than 600km from near the NT border almost to the coast south of Broome. The fire weaves around previous burns and cheekily finds small gaps of older, continuous fuel.

So without these earlier smaller controlled burns, the out-of-control fires would have been larger.

In the Great Sandy Desert of WA, the complex mosaic of spinifex of different ages persisted after these fires. The Indigenous Desert Alliance puts this down to more controlled burning in the past couple of years than in the ten years prior.

The fires of greatest concern to government agencies were the Barkly fires that threatened the town of Tennant Creek. These fires were large and fast-moving, feeding off fuel in a vast area of unmanaged country east of the town.

Here, a lack of land management increased disaster risk. The fire only stopped when it encountered four-year-old burned areas from lightning strikes.

The summer of 2023–24 was very wet across the Barkly and Tanami regions in the NT. Bushfires NT chief fire control officer Tony Fuller has warned of another big fire year to come as we head into the northern dry season of 2024.

Preparing for the future

Desert fire management is still under-resourced and poorly understood.

Ultimately the only effective way to prevent these massive fires in very remote parts of Australia is through a long-term, well-funded strategy of using fire over our vast desert landscapes to control fuel, as was done during previous millennia.

Rohan Fisher, Information Technology for Development Researcher, Charles Darwin University

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Some reports and popular books, such as Bill Gammage’s Biggest Estate on Earth, have argued that extensive areas of Australia’s forests were kept open through frequent burning by First Nations people. Advocates for widespread thinning and burning of these forests have relied on this belief. They argue fire is needed to return these forests to their “pre-invasion” state.

A key question then is: what does the evidence say about what tall, wet forests actually looked like 250 years ago? The answer matters because it influences how these forests are managed. It’s also needed to guide efforts to restore them to their natural state.

In a new scientific paper, we looked carefully at the body of evidence on the natural pre-invasion state of Australian forests, such as those dominated by majestic mountain ash (Eucalyptus regnans), the world’s tallest flowering plant. We analysed historical documents, First Nations Peoples’ recorded testimonies and the scientific evidence.

Our analysis shows most areas of mainland mountain ash forests were likely to have been dense and wet at the time of British invasion. The large overstorey eucalypt trees were relatively widely spaced, but there was a dense understorey of broad-leaved shrubs, tree ferns and mid-storey trees, including elements of cool temperate rainforest.

What was the evidence?

We looked at many sources of historical evidence. We read colonial expeditioners’ diaries. We reviewed colonial paintings and photographs. We sought out recorded and published testimonies from First Nations People. We compiled evidence from studies such as those that used carbon dating, tree rings and pollen cores.

We also examined the basic ecology of how the forests grow and develop, the plants’ level of fire sensitivity and different animals’ habitat needs.

As an example of the many accounts we found, 19th-century civil servant and mining engineer Robert Brough Smyth wrote about:

[…] heavily timbered ranges lying between Hoddle’s Creek and Wilson’s Promontory. The higher parts and the flanks of these ranges are covered with dense scrubs, and in the rich alluviums bordering the creeks and rivers the trees are lofty, and the undergrowth luxuriant; indeed in some parts so dense as to be impenetrable without an axe and bill-hook.

Similarly, in 1824, colonial explorers Hamilton Hume and William Hovell described their encounter with mountain ash forests at Mount Disappointment in Victoria:

Here […] they find themselves completely at a stand, without clue or guide as to the direction in which they are to proceed; the brush wood so thick that it was impossible to see before them in any direction ten yards.

The ecological and other scientific evidence suggests mountain ash forests evolved under conditions where high-severity bushfires were rare. As a result, mature forests of eucalypt trees of multiple ages dominated these landscapes. There was no evidence of active and widespread use of recurrent low-severity fire or thinning.

Our key conclusion is that these forests were not open or park-like – as was the case in some other vegetation types in Australia.

First Nations People knew not all Country needs fire

Importantly, tall wet forests were not wilderness. Rather, they were places of significance for First Nations People. They used these forests seasonally to access important sites and resources and as pathways to visit others in neighbouring Countries.

There is no doubt parts of Australia were subject to recurrent cultural burning for many diverse and important reasons before the British invasion. However, our discussions with Traditional Custodians in the Central Highlands of Victoria, including Elders, indicate cultural burning was not widely practised in most of the mountain ash forests there. Nor were these forests actively thinned.

Many First Nations People advocate the need to consider ecological responses to fire. The right fire (or not) for the right Country is a guiding principle of traditional fire management. In the words of Elder and cultural fire practitioner Victor Steffensen:

Aboriginal fire knowledge is based on Country that needs fire, and also Country that doesn’t need fire. Even Country we don’t burn is an important part of fire management knowledge and must be within the expertise of a fire practitioner.

Repeated burning, and even low-severity fire, is unsuited to the ecology of tall, wet forests. It can lead to their collapse and replacement by entirely different vegetation such as wattle scrub.

Similarly, thinning these forests can make them more fire-prone, not less, by creating a drier forest, and generate huge amounts of carbon emissions.

Thinning and burning will also destroy habitat for a wide range of species. They include critically endangered ones such as Leadbeater’s possum. Indeed, mountain ash forests are themselves recognised as a critically endangered ecosystem.

Let forests mature to restore what’s been lost

The compelling evidence we compiled all indicates mountain ash forests were dense, wet environments, not open and park-like, at the time of British invasion.

The use of scientific evidence is essential for managing Australia’s natural environments. Based on this evidence, we should not be deliberately burning or thinning these forests, which will have adverse impacts.

Rather, restoration should involve letting these forests mature. We should aim to expand the size of the old-growth forest estate to precolonial levels. Where regeneration has failed, practices such as planting and reseeding will be important to restore ecological values.

David Lindenmayer, Professor, Fenner School of Environment and Society, Australian National University; Chris Taylor, Research Fellow, Fenner School of Environment and Society, Australian National University; Elle Bowd, Research Fellow, Fenner School of Environment & Society, Australian National University, and Philip Zylstra, Research Associate, University of New South Wales, and Adjunct Associate Professor, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Once known only to those studying biology, the word symbiosis is now widely used. Symbiosis is the intimate relationship of different species living together. It’s much more common and older than many of us might realise.

One of the most common symbiotic relationships is between various species of algae and fungi, or between cyanobacteria (commonly known as blue-green algae though it’s not algae) and fungi. These paired species take the form of lichens.

The term symbiosis was first used in the 19th century to describe the lichen relationship, which was thought to be highly unusual. Since then, we’ve discovered symbiosis is the norm, rather than the exception. In fact, it has shaped the evolution of most life on Earth.

Symbiosis is almost everywhere we look

Lichens are diverse. They grow on tree trunks, on roof tiles and on ancient rocks.

The symbiosis of two different species allows both to survive in environments they might not be able to colonise otherwise. The fungus provides a suitable environment for its partnering species of algae or cyanbacteria to grow – it might otherwise be too exposed or dry, for example. In return, the fungus gets to share some of the carbohydrates produced by photosynthesis.

This is an example where both partners benefit from their relationship. It’s called mutualistic symbiosis.

Lichens are often very good indicators of air quality and more general ecosystem health. Their absence can indicate poor air quality. Because they absorb air pollutants such as heavy metals they can be used as biomonitors.

In another very common example of mutualistic symbiosis, most plant species live in a close relationship with fungi in the soil. It’s known as a mycorrhizal association.

The plants harness the energy in sunlight to make sugar from water and carbon dioxide in the process called photosynthesis. The plants share this food with the fungus, which relies on them for survival. In return, the fine threads of the fungus greatly increase the surface area of the plant roots for absorbing water and nutrients.

Not all partners benefit

Not all symbiotic relationships benefit both partners.

In parasitic symbiosis, one partner benefits at the expense of the other. Examples include the fungi Phytophthora, Fusarium and Armilleria, which often kill their plant hosts.

In cases of commensalism, one organism benefits and the other neither gains nor loses. Small birds, for example, sometimes perch on large herbivores, eating insects disturbed by the larger animals.

As in any relationship, it’s possible things can change over time. For example, a mutualistic symbiosis between a tree and its mycorrhizal fungus might change to parasitism as the tree ages and declines, or if environmental conditions change.

Symbiosis has driven evolution

Symbiosis has played a huge role in the evolution of life. The cells that make up the bodies of animals and plants are the result of symbiotic relationships.

Cells are complex. They contain structures called organelles, such as the nucleus (the control centre of the cell) and mitochondrion (involved in cellular respiration, which uses oxygen to break down food molecules to make energy available). Plant cells also contain chloroplasts, the sites of photosynthesis.

These complex cells evolved from much simpler, ancient forms of life that came together symbiotically.

The organelles of complex cells were once single-celled life forms that survived being engulfed by other simple cells. They formed a more complex and efficient cell, which has become the basic cell type for large multicellular life forms.

All large multi-cellular organisms living on Earth – animal and plant – possess this type of cell. It’s proof of how successful this evolutionary symbiotic strategy has been.

Cell respiration in both plant and animal cells involves mitochondria, which indicates they were engulfed early in evolutionary history. Later a cell type already containing mitochondria engulfed the chloroplast. This led to the evolution of complex plants.

When two become one

The incorporation of one cell type into another is called endosymbiosis. It allowed cells and parts of cells to become highly specialised. This specialisation improved their efficiency and capacity to survive under a wider range of conditions.

When I was a postgraduate botany student in the late ’70s, colleagues one day brought samples of common sea lettuce, Ulva latuca, to the laboratory, where I was studying photosynthetic physiology. Sea lettuce is a seaweed found in many shallow waters around the Australian coast.

We noticed a little marine slug grazing on the plant, so we popped it into our system for studying photosynthesis. To our surprise the slug was photosynthesising! We discovered the slug partly digested the sea lettuce cells, but some chloroplasts passed through the lining of the slug’s gut and continued to photosynthesise.

We thought we had made an important discovery, only to learn others had published similar work. After that I never doubted the validity of endosymbiosis, which was still a controversial theory at the time.

Symbiosis turns out to be the norm

We now know symbiosis is the norm for most organisms, including humans.

Our gut flora represent symbiosis on a massive scale. The diversity and huge numbers of bacteria living happily in our gut can have a huge impact on our general health and wellbeing. In the case of a healthy gut, both the person and the bacteria do well out of the relationship: a nice example of mutualistic symbiosis.

COVID focused public attention on viruses. But not all viruses are harmful; many actually benefit the organisms they infect. Some viruses even protect us from disease-causing viruses. For example, in people who are HIV-positive the disease progresses more slowly in those who are also infected with GB virus C (GBV-C).

Of course, the full range of symbiotic relationships with viruses is possible, from mutual benefit to an infected host suffering great harm. And, as with bacteria, there is accumulating evidence viruses have helped many species evolve, including our own.

An organism must live within a complex set of relationships to survive and thrive in any environment. Some relationships will be more positive than others, but it should not surprise that mutualistic symbiosis is so often the key to success.

Gregory Moore, Senior Research Associate, School of Ecosystem and Forest Sciences, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

To work in nature conservation is to battle a headwind of bad news. When the overwhelming picture indicates the natural world is in decline, is there any room for optimism? Well, our new global study has some good news: we provide the strongest evidence to date that nature conservation efforts are not only effective, but that when they do work, they often really work.

Trends in nature conservation tend to be measured in terms of “biodiversity” – that is, the variety among living organisms from genes to ecosystems. We treasure biodiversity not only for how it enriches society and culture, but also its underpinning of resilient, functioning ecosystems that are a foundation of the global economy.

However, it is well known that global biodiversity is decreasing, and has been for some time. Is anything we are doing to reverse this trend effective?

As part of a team of researchers, we conducted the most comprehensive analysis yet of what happened when conservationists intervened in ecosystems. These were interventions of all types, all over the world. We found that conservation action is typically much better than doing nothing at all.

The challenge now is to fund conservation on the scale needed to halt and reverse declines in biodiversity and give these proven methods the best chance of success.

First, the less good news

Globally, biodiversity is being depleted by human activities like habitat clearance, overharvesting, the introduction of invasive species and climate change.

To arrest its decline, people in various places have taken measures including creating protected areas, removing invasive species or restoring habitats, such as forests and wetlands. These efforts are interdependent with traditional stewardship of the world’s richest biodiversity by indigenous people and local communities. And in 2022, governments adopted new global targets to halt and reverse biodiversity loss.

Our team, led by the conservation organisation Re:wild, the universities of Oxford and Kent, and the International Union for the Conservation of Nature, analysed the findings of 186 studies covering 665 trials of different conservation interventions globally over the course of a century.

We wanted to understand whether the outcomes of these conservation actions improved on what would have happened without any intervention. Lots of studies have tried to compare the effects of conservation projects this way, but this is the first time such research has been combined in a single analysis to determine if conservation is working overall.

And now, the good news

What we found was extremely encouraging: conservation efforts work, and they work pretty much everywhere.

We found that conservation actions improved the state of biodiversity or slowed its decline in the majority of cases (66%) compared with no action. But more importantly, when conservation interventions work, we found that they are highly effective.

Examples from our far-reaching database included the management of invasive and problematic native predators on two of Florida’s barrier islands, which resulted in an immediate and substantial improvement in the nesting success of loggerhead turtles and least terns. In central African countries across the Congo basin, deforestation was 74% lower in logging estates subject to a forest management plan versus those that weren’t. Protected areas and indigenous lands had significantly less deforestation and smaller fires in the Brazilian Amazon. Breeding Chinook salmon in captivity and releasing them boosted their natural population in the Salmon River basin of central Idaho with minimal side effects.

Where conservation actions did not recover or slow the decline of the species or ecosystems that they were targeting, there is an opportunity to learn why and refine the conservation methods. For example, in India, removing an invasive algae simply caused it to spread elsewhere. Conservationists can now try a different strategy that may be more successful, such as finding ways to halt the drift of fragments of algae.

In other cases, where conservation action did not clearly benefit the target, other native species benefited unintentionally. For example, seahorses were less numerous in protected sites off New South Wales in Australia because these marine protected areas increased the abundance of their predators, such as octopus. So, still a success of sorts.

We also found that more recent conservation interventions tended to have more positive outcomes for biodiversity. This could mean modern conservation is getting more effective over time.

What comes next

If conservation generally works but biodiversity is still declining, then simply put: we need to do more of it. Much more. While at the same time reducing the pressures we put on nature.

Over half of the world’s GDP, almost US$44 trillion (£35 trillion), is moderately or highly dependent on nature. According to previous studies, a comprehensive global conservation programme would require an investment of between US$178 and US$524 billion. By comparison, in 2022 alone, subsidies for the production and use of fossil fuels – which are ultimately destructive to nature as fossil fuel burning is the leading cause of climate change – totalled US$7 trillion globally. That is 13 times the upper estimate of what is needed annually to fund the protection and restoration of biodiversity. Today, just US$121 billion is invested annually in conservation worldwide.

Potential funding priorities include more and better managed protected areas. Consistent with other studies, we found that protected areas work very well on the whole; studies that highlight where protected areas are not working often cite ineffective management or inadequate resources. More large-scale investment in habitat restoration would also help according to this new research.

Our study provides evidence that optimism for nature’s recovery is not misplaced. Though biodiversity is declining, we have effective tools to conserve it – and they seem to be getting better over time. The world’s governments have committed to nature recovery. Now, we must invest in it.

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Joseph William Bull, Associate Professor in Climate Change Biology, University of Oxford and Jake E. Bicknell, Senior Lecturer in Biodiversity Conservation, University of Kent

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Over the last 25 years, the ozone hole which forming over Antarctica each spring has started to shrink.

But over the last four years, even as the hole has shrunk it has persisted for an unusually long time. Our new research found that instead of closing up during November it has stayed open well into December. This is early summer – the crucial period of new plant growth in coastal Antarctica and the peak breeding season for penguins and seals.

That’s a worry. When the ozone hole forms, more ultraviolet rays get through the atmosphere. And while penguins and seals have protective covering, their young may be more vulnerable.

Why does ozone matter?

Over the past half century, we damaged the earth’s protective ozone layer by using chlorofluorocarbons (CFCs) and related chemicals. Thanks to coordinated global action these chemicals are now banned.

Because CFCs have long lifetimes, it will be decades before they are completely removed from the atmosphere. As a result, we still see the ozone hole forming each year.

The lion’s share of ozone damage happens over Antarctica. When the hole forms, the UV index doubles, reaching extreme levels. We might expect to see UV days over 14 in summers in Australia or California, but not in polar regions.

Luckily, on land most species are dormant and protected under snow when the ozone hole opens in early spring (September to November). Marine life is protected by sea ice cover and Antarctica’s moss forests are under snow. These protective icy covers have helped to protect most life in Antarctica from ozone depletion – until now.

Unusually long-lived ozone holes

A series of unusual events between 2020 and 2023 saw the ozone hole persist into December. The record-breaking 2019–2020 Australian bushfires, the huge underwater volcanic eruption off Tonga, and three consecutive years of La Niña. Volcanoes and bushfires can inject ash and smoke into the stratosphere. Chemical reactions occurring on the surface of these tiny particulates can destroy ozone.

These longer-lasting ozone holes coincided with significant loss of sea ice, which meant many animals and plants would have had fewer places to hide.

What does stronger UV radiation do to ecosystems?

If ozone holes last longer, summer-breeding animals around Antarctica’s vast coastline will be exposed to high levels of reflected UV radiation. More UV can get through, and ice and snow is highly reflective, bouncing these rays around.

In humans, high UV exposure increases our risk of skin cancer and cataracts. But we don’t have fur or feathers. While penguins and seals have skin protection, their eyes aren’t protected.

Is it doing damage? We don’t know for sure. Very few studies report on what UV radiation does to animals in Antarctica. Most are done in zoos, where researchers study what happens when animals are kept under artificial light.

Even so, it is a concern. More UV radiation in early summer could be particularly damaging to young animals, such as penguin chicks and seal pups who hatch or are born in late spring.

As plants such as Antarctic hairgrass, Deschampsia antarctica, the cushion plant, Colobanthus quitensis and lots of mosses emerge from under snow in late spring, they will be exposed to maximum UV levels.

Antarctic mosses actually produce their own sunscreen to protect themselves from UV radiation, but this comes at the cost of reduced growth.

Trillions of tiny phytoplankton live under the sea ice. These microscopic floating algae also make sunscreen compounds, called microsporine amino acids.

What about marine creatures? Krill will dive deeper into the water column if the UV radiation is too high, while fish eggs usually have melanin, the same protective compound as humans, though not all fish life stages are as well protected.

Four of the past five years have seen sea ice extent reduce, a direct consequence of climate change.

Less sea ice means more UV light can penetrate the ocean, where it makes it harder for Antarctic phytoplankton and krill to survive. Much relies on these tiny creatures, who form the base of the food web. If they find it harder to survive, hunger will ripple up the food chain. Antarctica’s waters are also getting warmer and more acidic due to climate change.

An uncertain outlook for Antarctica

We should, by rights, be celebrating the success of banning CFCS – a rare example of fixing an environmental problem. But that might be premature. Climate change may be delaying the recovery of our ozone layer by, for example, making bushfires more common and more severe.

Ozone could also suffer from geoengineering proposals such as spraying sulphates into the atmosphere to reflect sunlight, as well as more frequent rocket launches.

If the recent trend continues, and the ozone hole lingers into the summer, we can expect to see more damage done to plants and animals – compounded by other threats.

We don’t know if the longer-lasting ozone hole will continue. But we do know climate change is causing the atmosphere to behave in unprecedented ways. To keep ozone recovery on track, we need to take immediate action to reduce the carbon we emit into the atmosphere.

Sharon Robinson, Distinguished Professor and Deputy Director of ARC Securing Antarctica's Environmental Future (SAEF), University of Wollongong, University of Wollongong; Laura Revell, Associate Professor in Environmental Physics, University of Canterbury, and Rachele Ossola, Postdoctoral fellow, Colorado State University

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Seventy thousand years ago, the sea level was much lower than today. Australia, along with New Guinea and Tasmania, formed a connected landmass known as Sahul. Around this time – approximately 65,000 years ago – the first humans arrived in Sahul, a place previously devoid of any hominin species.

Due to the patchy nature of the archaeological record, researchers still don’t have a full picture of the routes and speed of human migration across the region.

In research published in Nature Communications, our team has reconstructed the evolution of the landscape during this time. This allowed us to better understand the migration strategies of the first peoples in what is now Australia, along with the places they lived.

Walking over a changing landscape

When trying to understand the dispersion of first humans in Sahul, one overlooked aspect has been the impact of the changing landscape itself.

Our planet’s surface is constantly shifted by various physical, climatic and biological processes, changing on a grand scale over geological time – a process known as landscape evolution.

We used a landscape evolution model that details climatic evolution from 75,000 to 35,000 years ago.

The model allows for a more realistic description of the terrains and environments inhabited by the first hunter-gatherer communities as they traversed Sahul.

On top of the evolving landscape, we then ran thousands of simulations, each describing a possible migration route.

We considered two entry points into Sahul: a northern route through West Papua (entry time: 73,000 years) and a southern one from the Timor Sea shelf (entry time: ~75,000 years).

From these simulations, we calculated the speeds of migration based on available archaeological sites. Estimated speeds range between 0.36 and 1.15 kilometres per year. This is similar to previous estimates, suggesting people spread across the continent quite rapidly.

For both scenarios, our simulations also predicted a high likelihood of human occupation at many of the iconic Australian archaeological sites.

Following rivers and coastlines

From the predicted migration routes, we produced a map of most likely visited regions, with probability of human presence as shown above.

We found that human settlers would have dispersed across the continental interior along rivers on both sides of Lake Carpentaria (the modern Gulf of Carpentaria). The first communities would have mainly been foraging along the way, following water streams. They also travelled along the receding coastlines as sea levels rose once more.

Based on our model, we didn’t identify well-defined migration routes. Instead, we saw a “radiating wave” of migrations.

However, our model did indicate a high likelihood of human presence near several already-proposed most likely pathways of Indigenous movement (called super-highways), including those to the east of Lake Carpentaria, along the southern corridors south of Lake Eyre, and traversing the Australian interior.

We could predict archaeological sites

There’s one particularly interesting outcome from our map that shows the probability of human presence in Sahul. In a cost-effective way (without needing to travel across the entire continent), it could potentially pinpoint areas of archaeological significance.

Our approach can’t tell us how well a given location might be preserved for archaeological finds. However, our simulations do give an indication of how much specific sites may have eroded or received extra sediment.

We could use this to estimate if artefacts at a potential archaeological site have moved or been buried over time.

Our study is the first to show the impact of landscape changes on the initial migration on Sahul, providing a new perspective on its archaeology. If we used such an approach in other regions as well, we could improve our understanding of humanity’s extraordinary journey out of Africa.

Tristan Salles, Associate professor, University of Sydney; Ian Moffat, Associate Professor of Archaeological Science, Flinders University; Laurent Husson, Earth sciences researcher, Université Grenoble Alpes (UGA); Manon Lorcery, PhD Candidate, Université Grenoble Alpes (UGA), and Renaud Joannes-Boyau, Professor, Southern Cross University

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