Climate change

Temperatures throughout Australia are continuing their long-term increasing trend, with the strongest warming occurring in the central and eastern interior of the continent (see the Climate chapter). On the other hand, temperatures have been locally stable or have decreased in some parts of north-west Australia where rainfall has increased substantially. Rainfall is generally decreasing in the south of Australia and increasing in the north, but with great variability over time. Severe drought affected many parts of eastern Australia from 2017 to 2019, extending to cover much of the continent in late 2018 and 2019 and easing over most areas during 2020.

Sea surface temperatures in the Australian region have also been increasing, and global sea level rise is accelerating. The impacts of climate change on Australian marine ecosystems are relatively well documented in comparison with terrestrial and freshwater systems. The Marine and Coasts chapters describe various impacts of climate change on biodiversity, such as the impact of marine heatwaves on marine ecosystems (see the Marine and Coasts chapters).

Climate impacts on terrestrial biodiversity

Useful information for Australia has been consolidated recently from local ecological knowledge and observations (Prober et al. 2019), assessment of long-term data where it exists (Greenville et al. 2018, Hoffmann et al. 2019), and direct observations of the impacts of climate change on biodiversity and ecosystems (Hughes et al. 2019). A collection of climate change anecdotes drawn from 326 observers from around Australia creates a picture of widespread, often subtle or gradual changes (lifecycle shifts, changing abundances, range expansions and contractions) across the continent, punctuated by extreme events such as fires, unprecedented droughts and other causes of mass mortality of biodiversity (Prober et al. 2019).

In many cases, the impacts of climate change on biodiversity are exacerbated by other pressures such as land clearing and invasive species, but in some cases impacts can be unequivocally attributed to climate change (Hughes et al. 2019).

Increases in extreme temperature events have been recorded across Australia. Data from the Australian Long Term Ecological Research Network have been used to examine ecosystem responses to changes in climate and disturbance regimes from plots in tropical savanna, alpine systems, temperate heathlands and temperate woodlands. A range of biodiversity responses to climate were recorded, including decreases in some species and increases in others. For example, in the Alpine Plot Network, the numbers of mountain pygmy possum (Burramys parvus), which is a specialised alpine species, declined significantly over the monitoring period (35 years). By contrast, the average number of bush rats (Rattus fuscipes), which is a generalist species that lives in many regions, almost doubled (Greenville et al. 2018).

Alpine ecosystems and biodiversity in Australia are particularly vulnerable to climate change that affects snow depth and the spatial and temporal extent of snow, which have all declined since the late 1950s (BOM & CSIRO 2020). Long-term monitoring of alpine vegetation in Australia has shown shifts in plant species composition and diversity, changes in the timing of flowering, and declines in endangered fauna such as the mountain pygmy possum (Hoffmann et al. 2019).

The ranges of the majority of Australia’s eucalypt species are predicted to shrink in size over the next 60 years (González-Orozco et al. 2016). Eucalypts are mostly endemic to Australia (i.e. found nowhere else) and dominate forest canopies and ecosystems across the continent. Approximately 90% of the current areas with concentrations of palaeo-endemism (i.e. places with eucalypt species that were once widespread and are now restricted to small ranges) are predicted to disappear or shift their location, and this is likely to have significant flow-on effects for ecosystem structure and function.

Climate change is increasingly recognised in threatened species recovery planning as a current and future risk. However, only a relatively small proportion of recovery plans that list climate change as a threat identify any specific actions to mitigate the threat, other than monitoring change (Hoeppner & Hughes 2019). Managing and reducing other threats that decrease the resilience of threatened species populations to climate change is often prioritised but rarely linked to the specific threats of climate change.

Climate impacts on aquatic biodiversity

Aquatic ecosystems and biodiversity are recognised as being among the most vulnerable to climate change. They experience both local changes and the cumulative effects of changes in the surrounding landscape, as well as exposure to a wide range of extreme climatic events such as floods and droughts. For example, between late 2015 and early 2016, mangroves along a 1,000 km stretch of coastline in the Gulf of Carpentaria in northern Australia suffered significant mortality. This happened during an underwater heatwave (which was also responsible for bleaching on the Great Barrier Reef) in combination with a severe drought and a temporary drop in sea level due to a strong El Niño event (Duke et al. 2017) (see the Marine heatwaves section in the Extreme events chapter).

Aquatic ecosystems in coastal areas are also affected by sea level rise and storm surge associated with intense storms. Along with structural changes and damage, these will bring changes in water salinity that can have long-term effects on wetland flora and fauna (Finlayson et al. 2017). Changes in salinity are likely to be particularly important in coastal regions because salinity tends to be a major influence on ecosystem composition, structure and function (see the Coasts chapter).

Altered water quality, as well as quantity, will be a major trigger for climate change effects on freshwater biodiversity. For example, the combination of hot conditions, low flows and significant algal blooms during the recent major drought (2018–20) resulted in mass fish kills in the Murray–Darling Basin (Koehn et al. 2020a). The recent extreme hot and dry weather events in the northern Basin have been amplified by climate change. Future changes in the global climate system are likely to have an even more profound impact on the hydrology and ecology of the Murray–Darling Basin, and increase the risk of fish deaths in the future (Vertessy et al. 2019).

Much of Australia has limited water resources, and there is limited scope for freshwater species to move to more favourable conditions as the climate changes. Species losses under future climates are likely to be high, particularly for inland regions of Australia. Climate change is predicted to cause substantial changes to the mix of species in Australian rivers well before the end of this century (James et al. 2017).

Changing fire regimes

Fire regimes across the globe are continually being modified due to changes in land use, land management and climate conditions. Fire regime components, including fire season, fire intensity and fire frequency, vary dramatically across Australia. Fire frequency can be as high as every year in some areas of the northern Australian savanna, whereas fire intervals may be measured in centuries in the highest rainfall areas of southern Australia. In the savannas, fire intensity varies with fire frequency and season, with the most intense fires occurring late in the dry season when fuel loads are high and conditions are at their most dry. Very high-intensity fires are usually only associated with low-frequency fire intervals in the tall eucalypt forests of southern Australia (see Bushfires – summer 2019–20).

Contemporary fire regimes are increasingly impacted by human activities and climate change. A clear trend towards more dangerous weather conditions for forest fires in Australia has been observed since the mid-20th century (Harris & Lucas 2019). The Forest Fire Danger Index (FFDI) is commonly used in Australia to assess weather. Aggregated over the fire season, the FFDI shows a significant increasing trend since the 1970s over most forested areas of south-eastern and south-western Australia (Abram et al. 2021). In general, this increase comes more from a lengthening of the fire season than from an intensification of the peak of the season. However, the number of days with a fire danger of very high or above has also increased. The exceptional 2019−20 fire season in temperate Australia occurred in a period when numerous indicators of fire weather aggregated over the season were at record high levels (see Bushfires – summer 2019–20). Recent evidence also indicates a trend in coastal south-eastern Australia for more frequent dry lightning events since 1979, a key natural source of wildfire ignition (Abram et al. 2021).

Indigenous fire management

Indigenous people use fire as a tool to manage landscapes, burning in different locations and seasons, at different times of the day and under different weather conditions to achieve specific cultural objectives (Ens et al. 2017). Following European arrival and removal of Indigenous people from their traditional lands, systematic traditional landscape fire management largely ceased. In the northern savannas, regional fire regimes shifted to extensive and very hot, late-dry-season fires. Over the past decade, Indigenous cultural fire management has been revived, particularly in central and northern Australia.

Methods to mitigate greenhouse gas emissions through shifting savanna burning to the early dry season are now being applied across northern Australia’s savannas (see case study: Western Arnhem Land Fire Abatement, in the Carbon capital assets section in the Land chapter). These methods are part of Australia’s emissions reduction strategy, and provide tradeable carbon credits through the Australian Government’s Carbon Credits (Carbon Farming Initiative) Act 2011 and subsequent Emissions Reduction Fund legislation. The savanna burning methodology is validated and approved within the zones where annual rainfall is 600–1,000 mm (low-rainfall zone) and above 1,000 mm (high-rainfall zone) (Figure 26a).

Many projects are operated by Indigenous people on Indigenous lands, using local Indigenous knowledge and customary burning practices (Ansell et al. 2020). The new programs provide a major source of untied revenue and employment opportunities in community and ranger activities (Ansell et al. 2020). In recent years, the adoption of these methodologies has led to a change in fire practices across northern Australia (Ansell et al. 2020) and subsequent overall decreases in fire size (Figure 27a), intensity and seasonality, along with an increase in the number of small mosaic fires during the early dry season (Figure 27b,c).

Use of traditional fire practice has extended into management regimes across Australia. Indigenous rangers are now involved in planned burns in all states and territories, particularly in the desert bioregions and in the forests and woodlands of the Australian Capital Territory, central Victoria, New South Wales and the Midlands of Tasmania. In southern Australia land tenure, habitat fragmentation and the increased risk posed by the complex mosaic of human habitation presents some unique challenges to the reinvigoration of traditional fire practices; nevertheless, programs are being implemented.

The co-benefits from savanna burning delivered to northern Australian Traditional Owners are derived through emissions abatement and carbon offset schemes, whereas in southern Australia the carbon co-benefits are through sequestration and the management of carbon stocks across the landscape. For many Traditional Owners, benefits also derive from discouraging weeds, recreating wildlife habitat, promoting bush tucker and minimising the opportunities for wildfire, all of which are culturally substantial and can be economically rewarding.

Impacts of changing fire regimes

Approximately two-thirds of species listed under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) in Australia are threatened by changing fire regimes (usually in concert with other pressures) (SG Kearney, University of Queensland, pers. comm., October 2020). The Threatened Species Scientific Committee is currently assessing ‘fire regimes that cause biodiversity decline’ as a key threatening process under the EPBC Act.

Although many Australian plant species are adapted to fire, sufficient fire-free intervals are needed to ensure that seed banks are adequately replenished to maintain future populations, and that juveniles of recruiting or resprouting plants become large enough to survive subsequent fires. Ongoing changes to fire conditions under future climates may expose many plant species to ‘interval squeeze’ – a narrowing of the favourable interval between fires, hence increasing local extinction risk by accelerating processes associated with population decline (Gallagher et al.). Conversely, the abundance of some plant species may decline where fire is excluded for too long. For example, fire intervals that are too short (less than 20 years) or too long (more than 50 years) both may result in reduced populations of the obligate seeder Callitris verrucosa (a conifer) within semi-arid mallee communities. Obligate seeders require fire to regenerate from seed in the soil. If fires are too frequent, juvenile plants are killed before they reach maturity to set seed; where fire intervals are too long, no new juveniles establish from seed and older plants die (Bradstock et al. 2006).

With changes in vegetation composition and structure, the suitability of vegetation for many animals species also changes (Clarke et al. 2021). For example, live mallee stems do not begin to produce hollows until 40 years after a fire, and the likelihood of mallee eucalypts containing hollows increases with age and reduces with repeat fires. Reducing the abundance of dead stems with hollows reduces the suitability of habitat for species such as microbats that depend on tree cavities in mallee vegetation (Senior et al. 2021).

However, many Australian animals are also resilient to a range of fire regimes, notwithstanding the significant immediate and long-term impacts of extreme bushfire events such as those that occurred in 2019–20 in southern Australia (see Bushfires – summer 2019–20). For example, across 6 replicated fire experiments in the savannas, very different fire regimes often had little or no detectable impact on species abundances. The most important effects of fire in the savannas was through habitat modification (Andersen 2021).

Extreme events

Many of the most significant impacts of climate change on biodiversity occur through extreme climate events. Scientists consider that trends in climate extremes may be more likely to trigger abrupt changes in ecological systems than trends in mean climate (Turner et al. 2020).

Long-term monitoring data from a wide range of Australian ecosystems show an increase in extreme climate events during the past decade (see the Extreme events chapter). Impacts can be especially severe when events are consecutive (occurring one after the other) or coincident (occurring at the same time). The increase in extreme events has resulted in many direct and indirect impacts on biodiversity (Greenville et al. 2018).

Heatwaves have intensified in Australia since 1950, with a consistent increase in peak temperature, number of events, frequency and duration (Trancoso et al. 2020). Wildlife and vegetation impacts due to extreme heat events are increasingly reported in both terrestrial and marine systems (Ruthrof et al. 2018, Ratnayake et al. 2019). In particular, Australia has experienced several marine heatwaves over the past 5 years, and the subsequent impacts on marine fauna and ecosystems such as kelp forests and coral reefs have received much public interest, as well as attention from researchers (see case study: Marine heatwaves, in the Extreme weather events section in the Marine chapter).

Knowledge about the impacts of extreme heat on terrestrial fauna and flora is limited to a few species, and most accounts are anecdotal through traditional or social media. Flying foxes feature prominently in reports of mass mortality from heatwaves. An extreme heatwave in north Queensland in November 2018 resulted in the deaths of an estimated 23,000 spectacled flying foxes (Pteropus conspicillatus) and 10,000 black flying foxes (P. alecto) over 2 days. The spectacled flying fox was uplisted from Vulnerable to Endangered in 2019.

The risk of bird mortality during heatwaves is predicted to increase substantially over much of Australia for the rest of this century (Conradie et al. 2020). This is compounded by unpredictable water availability under climate change, so that dehydration becomes a lethal factor. Birds may also abandon nests and lose body condition after heatwaves due to changes in food intake and because heat dissipation behaviours such as panting or wing spreading impair foraging efficiency (Sharpe et al. 2019).

Climate change is predicted to increase the intensity of tropical cyclones over the coming decades with compounding impacts from flooding rains and storm surges in coastal regions (see the Coastal erosion and inundation section in the Extreme events chapter) (see the Coasts chapter). Extreme convective storms that are often accompanied by hail are also likely to become more frequent (Bruyère et al. 2019) (see the Hail and convective storms section in the Extreme events chapter).

Bushfires – summer 2019–20

The bushfires that occurred through the ‘Black Summer’ of 2019–20 were unprecedented in their extent and severity (see the Extreme events chapter). Native species were severely affected, and continue to be affected, in many ways. The Australian Government committed $200 million to wildlife and habitat recovery following the bushfires.

Vast swathes of land were impacted by the bushfires, with approximately 6.5 million hectares of native forest burned in New South Wales, Victoria and the Australian Capital Territory, as well as grasslands, agricultural lands, commercial forest plantations and peri-urban areas. A further 2 million hectares of forest area was burned across Queensland, South Australia, Tasmania and Western Australia. Although eucalypt forests were most affected, rainforests and vine thickets, coastal heath, and grasslands were also burned. Mediterranean, subtropical and temperate bioregions were all affected (Godfree et al. 2021). The vegetation was estimated to contain habitat for 832 species of native vertebrate fauna (Ward et al. 2020).

Whereas most fires are patchy, leaving some areas less severely burned than others and even some patches unburned, aerial reconnaissance of the megafire revealed that vast expanses of vegetation were severely burned. This included relatively well-protected habitat that usually serves as refuges for species during fires, such as deep gullies, rocky outcrops and riparian strips (Wintle et al. 2020).

It is estimated that the fires affected significant proportions of at least 3 World Heritage properties, including 54% of the Gondwana Rainforests of Australia (Queensland and New South Wales), 81% of the Greater Blue Mountains Area (New South Wales) and 99% of Old Great North Road (an Australian convict site World Heritage property in New South Wales).

The full impact of the bushfires on biodiversity will not be known for many years, and the conservation status of many species thought to be secure will need to be reassessed.

Plants

The forests most affected by the fires are dominated by eucalypts and are among the most fire-prone in the world; however, only small percentages (less than 2%) usually burn each year, even in more extreme fire seasons (Boer et al. 2020). Although many Australian plant species have evolved with fire and are highly fire-adapted, the ability of plant communities and species to recover and regenerate after bushfires of the intensity and scale that occurred in 2019–20 is poorly understood (Godfree et al. 2021).

The 2019–20 bushfires increased the extinction risk of many plant species, including many that were already listed as Endangered or Critically Endangered under the EPBC Act. An assessment of the plant species most requiring urgent management intervention after the bushfires listed 486 Endangered or Critically Endangered species from a large variety of vegetation types, spanning rainforest shrubs to herbaceous plants from subalpine areas (Gallagher 2020b). These species all had more than 80% of their range burned, were listed as Critically Endangered or Endangered under the EPBC Act or equivalent state legislation, or were identified at high risk because of characteristics known to cause decline in plant populations.

Threatened ecological communities

For threatened ecological communities, 4 were assessed as having had more than 50% of their distribution within the mapped fire extent, and a further 3 had more than 30% of their distribution within the mapped fire extent (DAWE 2020b). The 4 most affected threatened ecological communities include wet sclerophyll forest, heathland, peatland and an aquatic root mat community in the caves of the Swan Coastal Plain; all are listed as Endangered. The 3 next most affected were grassy woodland and rainforest communities, and all are listed as Critically Endangered.

Animals

Nearly 3 billion animals are estimated to have been killed or displaced during the fires (van Eeden et al. 2020), including:

• 143 million mammals
• 2.46 billion reptiles
• 181 million birds
• 51 million frogs.

In January 2020, the Australian Government provided emergency funding support to zoos and wildlife carers to treat the injured wildlife and establish insurance populations for species at risk. Funding recipients reported that more than 9,000 animals were rescued, 3,700 treated and around 1,000 rehabilitated. More than 5,300 animals have since been released back into the wild.

The loss of food resources and shelter leaves many surviving individuals vulnerable to starvation and exposure to predators over the longer term. Increased competition with other individuals and species for the resources that remain can also affect survival.

An assessment focused on Australian fauna estimated that 378 birds, 254 reptiles, 102 frogs, 83 mammals and 15 freshwater fish have habitats in areas burned by the fires (Figure 28):

• 70 species had more than 30% of the habitat in their range burned and 21 of these were already listed as threatened
• 3 species had more than 80% of their habitat burned; 2 of these species are listed as Endangered under the EPBC Act – the Kangaroo Island dunnart (Sminthopsis griseoventer aitkeni) and the long-footed potoroo (Potorous longipes), while a third, Kate’s leaf-tailed gecko (Saltuarius kateae) has a small range and is not listed.

The Australian Government, through the work of its Wildlife and Threatened Species Bushfire Recovery Expert Panel, assessed the impacts of the bushfires on EPBC Act–listed threatened and migratory species (DAWE 2020b, DAWE 2020a). The March 2020 provisional list of animal species in need of urgent postfire management intervention covered 119 species: 23 reptile, 22 crayfish, 20 mammal, 17 bird, 16 fish, 16 frog and 5 invertebrates.

The priority animals were identified based on the extent to which their habitat has potentially been burned, whether they were already vulnerable to extinction, and the physical, behavioural and ecological traits that influence their vulnerability to fire. Preliminary assessments of species most affected indicate that 55 threatened and nonthreatened vertebrate taxa require detailed assessment or reassessment under the criteria of the EPBC Act.

Invertebrates

Initial assessments by the expert panel included a small number of invertebrates and a group of spiny crayfish because there were recent comprehensive accounts of their distribution and ecology, and many spiny crayfish species were known to require urgent management intervention to prevent extinction. However, information on many other invertebrate groups is lacking, making an assessment of post-bushfire risk challenging (Wildlife and Threatened Species Bushfire Recovery Expert Panel 2020).

An assessment of the overlap of threatened invertebrate distributions with the 2019–20 bushfire areas identified 191 invertebrate species known or presumed to have been severely affected by the fires; a further 147 species are recognised as priorities for further assessment because of concern about likely impacts. The 49 threatened invertebrates that are most fire-affected (more than 30% of their range has been impacted) span an extensive taxonomic range, including freshwater mussels, shrimps, burrowing crayfish, land snails, spiders, millipedes, bees, dragonflies, caddisflies, mayflies, bugs and butterflies.

An assessment of the impact of the bushfires on invertebrates in New South Wales identified 29 species (2 dung beetles, 3 archaeid spiders, 4 spiny freshwater crayfishes, 4 drosophilid flies, 5 mygalomorphs and 11 land snails) where all known occurrences are contained within the fire zone (Hyman et al. 2020). Another 46 species had at least half of their known range contained within the fire zone. Given these figures, the conservation status of many New South Wales species may require revision to recognise the higher level of threat, and active conservation actions will need to be taken to ensure the survival of these and other species.

Freshwater species

The 2019–20 bushfires were followed by above-average rainfall in many catchments, which moved ash and sediment into rivers and creeks (see the Bushfires section in the Inland water chapter). More than 43 catchments were burned across a range of landscapes. This contamination had a major impact on freshwater species.

Kills of 27 species of freshwater and estuarine fish, along with 4 species of crustaceans were reported from New South Wales and Victoria (Silva et al. 2020). These include at least 1 species listed as Endangered (trout cod – Maccullochella macquariensis) and 5 species listed as Vulnerable. Almost all estuarine sites with records of fish kills in this fire season were downstream of burnt areas.

Assessment Pressures of climate change and associated extremes on biodiversity

2021

Adequate confidence

Climate change is having increasing effects on Australia’s biodiversity, and the increased risk of fire and extreme events is likely to have the highest impacts. Related to United Nations Sustainable Development Goal targets 13.1, 13.2, 15.5

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Assessment Pressures from climate change on terrestrial species and ecosystems

2021

Adequate confidence

2016

2011

Pressure from climate change is increasingly recognised as a key threat to terrestrial ecosystems and species, and is projected to become more important in driving changes in terrestrial biodiversity into the future.

Assessment Pressures from climate change on aquatic species and ecosystems – southern, eastern and south-western Australia, including the Murray–Darling River

2021

Adequate confidence

The pressure from climate change on aquatic environments in southern and eastern Australia continues to have very high impact, with major effects on quantity and quality of surface water, recharge of groundwater resources, wetland environments, and Indigenous water values and cultural flows. The resilience of species and ecosystems in these environments is increasingly compromised as climate continues to change, and they are affected by extreme climate events and other pressures.

Assessment Pressures from climate change on aquatic species and ecosystems – northern and arid Australia

2021

Adequate confidence

Climate change is not a strong pressure on aquatic environments over large parts of northern and central Australia, although there may be localised high impacts.

Assessment Changing fire regimes

2021

Somewhat adequate confidence

2016

2011

Changing fire regimes are a major pressure on Australian biodiversity, including threatened species. Climate change is resulting in more extreme fire weather conditions and changes in intensity, frequency and seasonality of fires. However, we are increasingly managing landscapes across Australia to limit the impact from wildfires through managed and prescribed burning, incorporating cultural burning practices.

Assessment Extreme events

2021

Somewhat adequate confidence

A growing body of evidence supports the very high impact of extreme events on species and ecosystems. The increasing frequency and intensity of extreme events is likely to result in persistent, extensive and cumulative very high impacts into the future.