Climate change and extreme events

Over the past 5 years to 2021, climate change and extreme weather events have highlighted the vulnerability of human society; ecosystems and biodiversity, including freshwater and marine systems and other natural resources; industry, crops and agriculture; and urban, rural and coastal communities. Climate shifts that affect temperature and weather patterns, increased frequency and severity of extreme events, and other climate-related changes such as sea level rise are all having profound effects.

In 2021, Australia updated its nationally determined contribution to the United Nations Framework Convention on Climate Change, affirming a target of net zero emissions by 2050.

Australia also reaffirmed its 2030 target of 26–28% reduction in greenhouse gases on 2005 levels and stated that it will exceed this target by 9% (DISER 2021a). The nature and concentrations of future global emissions will have a major effect on the trajectory of climate change in the second half of the 21st century.

Assessment Climate change

2021

There is a general shift across Australia towards higher land, air and sea temperatures; more acidic oceans; rising sea levels; and less rainfall in southern Australia. Bushfires and heatwaves (both land and sea) are increasing in frequency and intensity. Other extreme events are changing in their frequency, intensity and distribution. It is anticipated that pressure from climate change will continue to increase.
Assessments of impact range from high to very high
Assessments of trend range from deteriorating to stable
Related to United Nations Sustainable Development Goal targets 6.1, 6.5, 7.2, 11.4, 11.b, 13.1, 13.2, 14.3, 15.5

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Greenhouse gas emissions

Warming of the Australian climate, and associated changes in the climate system, are driven by increased concentrations of greenhouse gases in the atmosphere. Changes to the climate are inevitable, based on greenhouse gases that have already been emitted, but further changes in the second half of the 21st century will depend on the level of future global emissions.

Globally, atmospheric concentrations of greenhouse gases continue to increase, driving climate change, warming on land and in the oceans, and, in turn, rises in sea levels as warmer water expands and polar ice caps melt. Although Australia’s emissions have decreased from their 2007 peak, mostly due to changes in land use and the rapidly increasing share of renewables in electricity generation, progress on emissions reductions has stalled since 2013 (DISER 2020c). A sudden drop in emissions due to restrictions on human activity and travels during the COVID-19 pandemic is expected to be temporary. Before the pandemic, transport-related emissions grew steadily, especially as a result of increases in diesel use and the uptake of larger light commercial vehicles.

Australia contributes approximately 1.2% of global emissions. This places us among the top 15 total emitters, and we are among the world’s largest per-person emitters (Global Carbon Project 2019). It is not clear whether the current trend will enable Australia to meet its current nationally determined contribution of a 26–28% decrease by 2030 and our recent commitment to net zero emissions by 2050 (Figure 12).

Emissions from electricity generation are the largest source of emissions in Australia (34%), but have been falling since 2016 driven by large amounts of renewable capacity entering the market (DISER 2021b). Stationary energy emissions have increased since 1990 at an average rate of 1.4% per year but are projected to remain relatively stable until 2030 (DISER 2021b). Emissions trends in the energy sector are rising, mainly driven by liquefied natural gas production, which accounted for 70% of emissions in the energy sector in 2019 and is projected to increase to 75% by 2030 (DISER 2021b) (see Figure 18 in Energy production).

Climate shifts

Climate change comprises long-term, gradual shifts in climate together with changes in episodic extreme events. Gradual shifts in climate are occurring across a range of parameters, including land, sea and air temperatures, and rainfall patterns. These changes are causing high pressures on the environment, and the situation is deteriorating.

The warming of the Australian continent and sea surface has continued unabated, accompanied by unprecedented weather extremes and associated disasters, with devastating consequences for the environment, the economy and the Australian people.

The Australian climate has warmed by a mean of 1.4 °C on land and 1.1 °C in the oceans since consistent national records began. Most of the increase in temperatures over Australian land areas has occurred since the 1950s, and temperatures have continued to increase over the past 5 years. Australia’s warmest year on record was 2019, with temperatures 1.52 °C above the average for the standard 1961−90 reference period. The decade from 2011 to 2020 was Australia’s warmest on record, and every individual year from 2013 to 2020 ranks in the 10 warmest on record nationally. Although some parts of Australia are warming faster than others, almost all areas are warming in all seasons (BOM 2020a).

On land, the strongest warming has occurred in the central and eastern interior of Australia, and the slowest in north-eastern Australia and some south-eastern coastal regions, including Tasmania (BOM 2020a). Marine warming was slightly higher in eastern Australian waters than in the west, and the western Tasman Sea has warmed especially quickly (Blunden & Boyer 2020). Many natural systems face major challenges from temperature increases, with species and ecosystems forced to move, adapt or die.

Rainfall has decreased since 1970 in southern Australia; the decreases have been strongest in the cool season, placing substantial stresses on water availability in these regions. Over the same period, rainfall has increased in north-western Australia. In other parts of Australia, a clear trend has not emerged beyond the range of natural interannual to decadal variability.

While these changes are occurring against a backdrop of Australia’s climate and system variability, climate change is also having a high impact on that variability, including the seasonal, interannual, decadal and longer changes in key factors such as water temperature, rainfall patterns, surface winds and oceanic currents (Evans & Hobday 2021). Continued climate change is expected to exacerbate such variability, leading to more intense extremes (Matear et al. 2021).

Climate change disproportionately affects Indigenous communities, which have reported seasonal changes, rising seas, temperature increases, reduction of food and water resources, and loss of Country and access to Country. Climate change impacts Indigenous people’s ability to practise culture (Seed 2021). In 2021, Torres Strait Islanders from Boigu and Saibai islands commenced the first climate change class action against the Australian Government, alleging failure to protect them and their low-lying islands from climate change that now threatens their homes (SBS News 2021).

Other climate-related changes

Other profound environmental changes are occurring that are related to the changes we are seeing in our atmosphere and climate.

Climate change is influencing the potential for fire in the landscape. Seasonal fire periods are becoming longer; in New South Wales, for example, the bushfire season now extends to almost 8 months, not including hazard reduction burning (OEM 2018). Climate change is also resulting in a greater frequency, severity and overall unpredictability of bushfires. The number of days with very high or above fire danger has also generally increased (Figure 13) (CSIRO & BOM 2020). The exceptional 2019−20 fire season in temperate Australia occurred during a period when numerous indicators of fire weather aggregated over the season were at record highs.

Our oceans are absorbing about 25% of the annual global carbon dioxide emissions (see Greenhouse gas emissions). This is changing the chemistry of the ocean, reducing its alkalinity (increasing its acidity – known as ocean acidification). Ocean acidification influences the ability of marine animals to build their calcium shells or skeletons (such as a coral’s hard skeleton). Conditions on the inner-central Great Barrier Reef are approaching a tipping point, forecast to cause a decline in coral juveniles and increased macroalgal cover (Fabricius et al. 2011, Fabricius et al. 2020, Smith et al. 2020).

Because Australia is an island nation with much of its development on the coast, sea level rise caused by the expansion of the warming ocean and the melting of polar ice is a significant threat. One of the most significant predicted impacts of sea level rise on Australia’s coasts is erosion and the movement of beaches, and the permanent inundation of low-lying areas.

Pressures from sea level rise are currently low, but the situation is deteriorating. Sea level rise at Australia’s coastline is above the global average of 3–3.5 millimetres per year (Green et al. 2010, Suppiah et al. 2011, TSRA 2014, Rainbird 2016). Globally, sea levels have risen by 19 centimetres since 1901. In Australia, the rate of rise varies around our coast and is accelerating, with some parts of Australia seeing rises of 4–6 millimetres per year. Over 2014–2100, it is projected that global sea levels will rise by 28–55 centimetres relative to the average level if greenhouse gas emissions are low, and by 63–102 centimetres if emissions are high (IPCC 2021). The predictions for Australia are similar or slightly higher, but also vary regionally around Australia (IPCC 2014).

Although sea level rise itself is not an extreme event, it can exacerbate the impact of extreme events, such as storms and heavy rainfall, on Australia’s highly populated coastal plains. Sea level rise caused by global climate change is a chronic change facing all coastal communities.

Climate change is of significant concern for many Indigenous communities around Australia, especially the low-lying islands of Torres Strait (O’Neill et al. 2012) that are vulnerable to rising sea levels. Indigenous peoples have acquired knowledge about the environment and its changes for more than 60,000 years, including adaptation responses (Bird et al. 2013). The survival of Indigenous peoples over this time means that cultural and traditional knowledge has been passed down during some periods of rapidly changing climate conditions (Charles & O’Brien 2020); however, this knowledge has remained largely undervalued (ESCC Hub 2021). Recently, a number of national Indigenous events were convened to talk about climate change and the threats to Country. The National First Peoples Gathering on Climate Change 2021 noted impacts on seasonal weather patterns, cultural practice, resources and sea levels. In October 2021, the Lowitja Institute, in partnership with the National Health Leadership Forum and the Climate Change Alliance, held a Climate Change and Aboriginal and Torres Strait Islander Health Roundtable discussing the impacts of climate change on health and wellbeing (HEAL Network & CRE-STRIDE 2021).

Extreme events

The intensity and frequency of extreme weather–related events – including heatwaves, droughts, bushfires and floods – are changing. Since the 2016 state of the environment report, ongoing increases in land and sea temperatures across Australia driven by climate change have coincided with multiple extreme weather events. These have had devastating impacts on many of Australia’s unique natural ecosystems and caused the death of many individuals of many species, while also bringing new growth and stimulus for reproduction. For example, floods associated with massive rainfall in northern Australia in early 2019 caused extensive social and economic cost in northern and western Queensland (estimated at $5.68 billion), but also reached the Kati Thanda–Lake Eyre system and filled the northern lakes, triggering large pulse-breeding responses in wildlife such as birds, and freshwater fish and frogs.

Modelling based on historical and archaeological events and climate scenarios suggests that many extreme events will increase in intensity and frequency, with a potential expansion in their distribution, changes in their duration, and increasing complexity of linked impacts. Some events, such as tropical cyclones and east coast lows, are forecast to become less frequent but potentially more intense (CSIRO & BOM 2020). Research into the relationship between human-induced climate change and extreme weather events suggests that the risk of most observed extreme heat and cold events has been significantly altered by climate change. Although extreme events can have positive effects on some systems, their increasing intensity may overwhelm systems, leading to a more negative overall impact. It may also negate the positive impacts of occasional disturbances, which can stimulate colonisation, growth and reproduction.

The effects of extreme events on all aspects of the natural and urban environments are well known (see Landscapes and seascapes). Perhaps less well understood are the cumulative effects of multiple forms of extreme events on other stressors of the environment (see Cumulative pressures). For example, the impacts of feral animals can inhibit recovery of different species and communities after fire; increased mortality of some species after bushfires is primarily due to increased predation by invasive predators (cats, foxes) as a result of loss of groundcover.

There is growing recognition of the role Indigenous people can play in dealing with extreme events and mitigating impacts on their communities, and cultural and environmental values. Significant areas of land are returning to Indigenous ownership or joint management through land rights, native title and Indigenous Protected Areas (see Indigenous tenure). The Indigenous population is widespread, and Indigenous communities are disempowered as a result of many factors, such as remoteness, lack of adequate housing and infrastructure, racism, continuing impacts of colonisation, and socio-economic and health disparity with non-Indigenous communities. Despite this, Indigenous communities display great resilience and have longstanding connections to their Country. They hold traditional knowledge and continue customary practices that can assist in planning, response, recovery and resilience to climate change and extreme events.

Heatwaves

There is a broad nationwide trend towards a much higher frequency of very hot days. For example, in Victoria, the average number of days per year on which the temperature has reached 45 °C increased from 0.3 in 1961−2000 to 2.6 in 2011−20. Extreme and extensive heatwaves occurred in many parts of Australia in the 2018−19 and 2019−20 summers, exceeding historical records. The heat was particularly notable for the large area that it covered, which led to unprecedented daily temperatures averaged over Australia.

Elevated temperatures impact all living things and are known to increase mortality in human populations. Heatwaves cause more human deaths in Australia than any other single extreme weather event (Steffen & Hughes 2013). Australia’s potential vulnerability to heat exposure is high and increasing, with total deaths, lost working hours and mental health outcomes all increasing with higher temperatures (Beggs et al. 2019).

Vulnerable ecosystems and native animals are susceptible to both the direct and indirect effects of heatwaves, and heat stress has been responsible for large numbers of deaths of native species since 2016 – for example, the mass deaths of flying foxes in Queensland in late 2018. Heat stress also affects plant productivity, and agricultural enterprises have already begun diversifying where they grow certain crops for future market resilience. Elevated temperatures also affect freshwater systems and interact with drought, contributing to fish deaths in stressed waterways, and increasing bushfire risk and intensity. Heatwaves played a role in the 3 devastating fish death events in the extensive Menindee Lakes system on the Darling River in western New South Wales in 2018–19, in which more than 1 million fish died.

Ocean warming has contributed to recent record-breaking marine heatwaves (Santoso et al. 2017) – these are events in which seawater temperatures exceed a seasonally varying threshold (the 90th percentile) for at least 5 consecutive days (Hobday et al. 2016). The global annual number of marine heatwave days has risen by 54% over the past century, with 8 of the 10 most extreme marine heatwaves ever recorded occurring after 2010 (Smith et al. 2021b). Marine heatwaves have dramatic impacts on marine life, resulting in major ecological impacts such as changes to species’ distribution, reproduction success and persistence in some habitats. This has flow-on effects on industries; it is estimated that economic losses from a single marine heatwave event can exceed US$900 million (Smith et al. 2021b).

Marine heatwaves were recorded on the Great Barrier Reef in 2015–16, 2016–17 and 2020, and were accompanied by significant coral bleaching events (BOM 2020d). In 2015–16, a northern Australia marine heatwave was the longest on record in the south-east tropical Indian Ocean (Benthuysen et al. 2018), with coral bleaching off north-western Australia (Gilmour et al. 2019). During 2020, marine heatwaves occurred in most shelf areas around Australia, with many regions reaching category 2 (strong) (WMO 2021). Marine heatwaves have contributed to a decline in environmental state in both temperate and tropical waters on both the west and east coasts. The waters south-east and south-west of Australia are recognised as global hotspots, with rates of warming above the global average (Hobday & Pecl 2014).

Drought

Although there was some recovery following the millennium drought (2000–10), hot, dry conditions resulted in severe drought affecting much of Australia over 2017–19. The most acute dry conditions occurred in the northern Murray–Darling Basin, where annual rainfall in 2019 was 70–80% below normal, and more than 40% below previous record lows. It was also exceptionally dry over much of Australia’s interior, where numerous locations had less than 30 millimetres for the year. Although Australia has experienced longer droughts, this event was more intense over a 2–3-year period.

Bushfires

The interaction of drought and heatwaves means that much of Australia is experiencing more extreme fire weather days (CSIRO & BOM 2020); increases in the length of fire seasons; and increases in the frequency, severity and unpredictability of bushfires.

A study of the catastrophic 2019–20 bushfires (known as the ‘Black Summer‘ fires) found that climate change had induced a higher weather-related risk than in previous years (Binskin et al. 2020, BOM 2020c, van Oldenborgh et al. 2021). Several years of severe drought across much of Australia preceded the hottest and driest year on record in 2019. Temperatures exceeded historical records, particularly during the 2018−19 and 2019−20 summers, when extreme, expansive heatwaves were reported across much of Australia. Numerous high-temperature records occurred at individual sites across southern and eastern Australia.

The hot conditions combined with the dry landscape and strong winds to produce dangerous fires during December 2019 into early January 2020.

The Black Summer fires were exceptional for the scale, severity and synchrony of fires across southern and eastern Australia (Figures 14 and 15). Fires burned simultaneously across multiple Australian states and territories. Thirty-four human lives were lost (Binskin et al. 2020), and some 2,500 homes were destroyed. An estimated 417 additional deaths were attributed to bushfire smoke (Borchers-Arriagada et al. 2020, Johnston et al. 2020) and about 80% of the Australian population was affected by bushfire smoke at some point during the season; smoke travelled 11,000 kilometres offshore to South America and is estimated to have added up to 900 million tonnes of carbon to the air (Filkov et al. 2020). Canberra experienced the worst outdoor air quality measurements of anywhere in the world (Filkov et al. 2020); daily PM_2.5 concentrations on 1 January 2020 – the worst day during the bushfire period – were 38.5 times the 24-hour National Environment Protection Measures standard.

More than 10.3 million hectares of native bushland was burned (ABARES 2021), as well as grasslands, agricultural lands, commercial forest plantations and peri-urban areas (Davey & Sarre 2020). Some 8 million native animals were lost in New South Wales alone, and it is estimated that a total of 1–3 billion animals were killed or displaced during the fires (Dickman et al. 2020, WWF-Australia 2020). The bushfires increased the extinction risk of many plants and animals, including many that were already listed as Endangered or Critically Endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) or state legislation. For example, 486 species of threatened plants (Gallagher 2020), 23 reptiles, 22 crayfish, 20 mammals, 17 birds, 16 fishes, 16 frogs and 5 invertebrates were identified as requiring urgent management intervention following the bushfires (DAWE 2020e, DAWE 2020f). Four threatened ecological communities 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; 18 Key Biodiversity Areas had 15% or more of their habitat burned (see also World Heritage) (Todd & Maurer 2020).

Other weather extremes interact with bushfires, exacerbating pressures on natural and human environments. For example, the above-average rainfall that followed drought and fires across much of eastern Australia in 2020 compounded pressures on waterways. Rainfall run-off through burnt firegrounds carried sediment loads rich in ash, nutrients, organics and metals, putting water and sediment quality at risk in inland and coastal ecosystems, including drinking water catchments. In the Upper Murray catchment in south-eastern New South Wales and north-eastern Victoria, nearly one-third of forested and rural regions were burned. When rain fell, high loads of sediment and ash entered the Murray River and Lake Hume, causing local mortality of fish, reducing the hatching success of key crustacean food sources and causing high mortality of freshwater snails (Joehnk et al. 2020). Mortalities across 15 waterways in New South Wales and Victoria were seen in at least 27 species of fish and 4 crustacean species. The sediment-laden run-off entering coastal waters caused stratification and delayed algal growth in some New South Wales estuaries in response to the increased nutrient and carbon loads. Few studies have yet looked at the impact of the toxins generated from the bushfires on aquatic organisms, although research to fill these gaps was underway in many states by 2021.

Storms, floods and cyclones

An increase was observed in certain types of rainfall extremes over 2017–19 (CSIRO & BOM 2020). The intensity of short-duration (hourly) extreme rainfall events increased by around 10% or more in some regions and in recent decades. Daily rainfall totals associated with thunderstorms have increased since 1979.

Flooding is one of the costliest extreme events because rising water levels can damage agriculture, buildings and infrastructure; disrupt supply chains; displace people; and threaten human life. Floods also cause erosion and deposition in natural environments. For human endeavours, they can be catastrophic; however, floods are also frequently life giving. Floods are essential for groundwater recharge in some systems, and, in natural landscapes and some agricultural contexts, floods are a key part of the lifecycle – some species depend on floods to distribute seeds, fill temporary waterholes and stimulate population explosions.

For example, prolonged rainfall associated with the 2019 northern Australia monsoonal trough caused the most significant flood event in 50 years in Queensland’s longest river, the Flinders River, resulting in floodwaters 700 kilometres long and 70 kilometres wide (IGEM 2019). The 2019 floodwaters reached the predominantly dry Lake Eyre system in South Australia and filled its northern lakes, triggering a massive wildlife response in freshwater fish, frogs and birds. Floodwaters flowing north into the Gulf of Carpentaria also carried large quantities of organic matter and detritus, which triggered a population boom in some coastal fisheries.

Cyclones reduce productivity in both natural environments and agricultural operations, with flow-on effects on habitats and food resources for wildlife, and on human populations and economies. Disturbances also enable weed species to invade recovering vegetation (Murphy & Metcalfe 2016). Cyclones damage coral and seagrass beds, wash fish and marine mammals ashore, and reshape coastal and intertidal communities such as mangrove forests. For example, because the 2017 category 4 cyclone Debbie was slow moving, gale-force winds gusting at more than 200 kilometres per hour persisted near some of the reefs near the Whitsunday Islands for up to 56 hours, resulting in an average loss of coral cover of 70% at a depth of 2 metres, and up to 98% loss in some areas (GBRMPA 2019). Billions of dollars of damage to homes, infrastructure and industries included losses of approximately $500 million to agriculture.

The pressure imposed by tropical cyclones on natural and human systems is stable but deteriorating. The forecast for Australia is for a similar frequency of tropical cyclones, but their intensity and associated rainfall will increase (Chu et al. 2020, Pepler & Dowdy 2021), and they may track further south (Bruyère et al. 2020). Between January 2016 and December 2020, 35 tropical cyclones occurred in the Australian region, with 16 making landfall on mainland Australia or island territories (BOM 2021d).