Temperature

Warming temperatures are the clearest manifestation of climate change. Almost everywhere on the globe has warmed over the past century. Both land and ocean areas have warmed, but in general land areas are warming faster than oceans. The Arctic is the world’s fastest-warming area, while the Southern Ocean is among its slowest. Globally, temperatures averaged over 2011–20 are 1.09 °C higher than in 1850–1900; land temperatures have warmed by 1.59 °C and sea surface temperatures by 0.88 °C (IPCC 2021).

The Bureau of Meteorology and CSIRO produce a biennial state of the climate report, which was most recently published in 2020. This section draws on the climate information used in that report.

Land temperatures

Temperatures over Australian land areas continue their long-term increasing trend. Since consistent national records began in 1910, mean temperatures over Australia have increased by approximately 1.4 °C (BOM 2020b), with most of the increase occurring since the 1950s. The rate of warming over Australia is close to the global average for land areas.

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 (Figure 1).

Since 1910, mean temperatures have increased over all parts of Australia and in all seasons (Figure 2):

  • The strongest warming, exceeding 2 °C in places, has occurred in the central and eastern interior. Many parts of inland New South Wales and southern Queensland have warmed by more than 1 °C since 1980.
  • The slowest warming, of 0.5–1 °C, has occurred in some parts of north-western Australia, and in some south-eastern coastal areas (including Tasmania).
  • In the most recent decades, mean temperatures have been locally stable or declining in some parts of north-western Australia, where rainfall has increased substantially (see Rainfall and snow). Winter minimum temperatures have been relatively stable in parts of inland south-eastern and south-western Australia, where cool-season rainfall has decreased.

Most Australian Antarctic and subantarctic sites have warmed since the mid-20th century, although more slowly than most Australian mainland locations. Mawson and Davis stations, on the Antarctic continent, and Macquarie Island have all warmed by about 0.5 °C since records there began in the 1950s. However, Casey Station has cooled by about 0.6 °C since it opened in 1970. (see the Antarctica chapter)

Figure 1 Annual mean temperature anomaly (difference from the 1961−90 average), 1910–2020
Figure 2 Trend in mean temperature, 1910–2020
Assessment Temperature increases

Impacts of higher land temperatures

Rising temperatures on land have a range of impacts. Whereas some of these are manifested in extreme events such as heatwaves (see High temperatures), others depend on long-term changes in temperature.

Signals are emerging of climate change impacts on various indicators of biodiversity, such as species distributions, lifecycles and population dynamics. Some of the strongest signals are found in high-altitude communities where there is limited scope for species to move to cooler locations (see the Biodiversity chapter). The geographical range of various agricultural activities has also moved in response to climate change; some of the most significant changes are occurring in temperature-sensitive industries such as viticulture (see the Land chapter).

Indigenous people also experience the impacts of rising temperatures. Although temperature increases felt by Indigenous people are the same as global changes, the impacts from warmer temperatures also lead to extreme cultural change for Indigenous people, as a result of biodiversity loss, loss of culture, and changed cultural patterns of living and travelling in and across their Country. With land areas warming faster than oceans, Indigenous people reasonably fear becoming Australia’s first climate refugees:

Without action to stop climate change, people will be forced to leave their Country and leave behind much of what makes them Aboriginal. Climate change is a clear and present threat to the survival of our people and their culture. (Allam & Evershed 2019)

Rising land temperatures can reduce the availability and growth of plants used for traditional purposes such as food and medicines; this can affect the health of Indigenous people who rely on traditional plants for their nutritional and healing properties. Regardless of whether these plants are resilient to climate change, the impacts on their availability and accessibility in the environment are critical.

Case Study Yorta Yorta weaving

A changing climate, changing water management practices and environmental change are all impacting the way in which the Yorta Yorta people access, harvest and use one of their traditional weaving sedges (Carex tereticaulis). Most of their Country is developed; land-use activities vary from multiple crop species of wheat and corn to dairy farms.

Figure 3 Long-term climate records at Deniliquin, New South Wales, for (a) annual average maximum temperature and annual average minimum temperature; (b) the total annual rainfall (bars) with 11-year running mean

Source: Bureau of Meteorology, 2021

The weaving sedge is an ephemeral aquatic species that relies on regular seasonal watering from the Murray River, its associated waterways and rainfall. It grows throughout the area, known as Barmah. The Yorta Yorta people refer to this area as Pama.

The weaving sedge relies on multiple factors to maintain conditions that are favourable for healthy growth, such as inundation with water, soil health, climate and rainfall. A changing climate and changing water regimes are affecting the resilience of this species and, therefore, the availability of this important plant for traditional knowledge and cultural use by the Yorta Yorta people. Records show 2 important climatological events in south-east Australian history: the ‘federation drought’ at the turn of the 20th century and the ‘millennium drought’ at the turn of the 21st century (Griggs et al. 2014). They also show that a pattern of episodic flooding was evident before settlement and that cultural uses of traditional plant species were affected by these drier episodes (Griggs et al. 2014).

The impacts of low rainfall, hotter summers and a changing climate are evidence that these species are struggling to survive. This means that the Yorta Yorta people cannot harvest at this site and use the species in the same traditional setting as they had once done. Yorta Yorta Country and the weaving sedge are forced to adapt to change, and the Yorta Yorta people are forced to adapt as a result of these changes:

If this plant is no longer available on Country, then my connection to my heritage and our traditional practices have been impacted. If the plants are healthy, we can harvest the reed for weaving. If the plants are not healthy, the reeds won’t be healthy and cannot be used. This tells us that there is something wrong. This is our barometer check of healthy Country. (Denise Morgan-Bulled, 2020)

While improved water management and rainfall are seen as critical to supporting the weaving sedge, fire was recently applied to the sedge to see whether the recovery of this species was possible under adapted conditions:

To see Country burn – I felt a sense of calm; to see and feel fire – my skin felt good; to see and smell smoke – I felt I could breathe; to stand on Country – I felt strong. Country felt good that day, I felt good that day. (Sonia Cooper, 2020)

Immediately after the burn, rain fell and some parts of the forest were inaccessible, and some new growth was triggered. This project allowed the influence of fire to be investigated as an additional management tool to help recover the species. The response of the weaving sedge to fire provided cultural outcomes for traditional weaving species for the Yorta Yorta people.

Figure 4 (a and b) New tussock, Carex tereticaulis, growth through burnt Carex. (c) Unburnt C. tereticaulis new shoots after rain

Photos: S Cooper, 2020


Ocean temperatures

Sea surface temperatures in the Australian region have been increasing. Since 1900, they have risen by approximately 1.1 °C (Figure 5). As on land, most of the increase has been since the 1950s. Sea surface temperatures have risen more slowly than temperatures on land. This is consistent with the situation globally, where land has warmed at 1.8 times the rate of the ocean (IPCC 2021).

The rate of warming is fairly uniform across all seasons, and is generally slightly higher in eastern Australian waters than in the west. The western Tasman Sea has warmed especially quickly in recent decades, with some areas having warmed by more than 1 °C since 1980. In the Coral Sea region, which contains the Great Barrier Reef area, the rate of warming is similar to the national average. Ocean heat content, an indicator of temperature through the full depth of the ocean, has also increased over 1993–2020; the strongest increases, as at the surface, are in the western Tasman Sea (Blunden & Boyer 2020).

Although changes in sea surface temperatures at decadal and longer timescales are broadly consistent with temperature changes on land, land and sea surface temperatures can differ substantially in individual years. For example, although 2019 was Australia’s warmest year on record on land, Australian sea surface temperatures in 2019 were the lowest since 2008 (Figure 6). This variation is in part because land and sea temperatures are affected in different ways by the El Niño–Southern Oscillation and Indian Ocean Dipole. For example, La Niña is associated with below-average temperatures on the Australian continent, but above-average temperatures in northern Australian waters. The 3 warmest years on record for Australian region sea surface temperatures – 2016, 2010 and 1998 – have all come at the end of significant El Niño events.

Figure 5 Sea surface temperature trends in the Australian region: (a) 1910–2020; (b) 1980–2020
Figure 6 Temperatures in 2019 compared with average for 1961–90

Note: 2019 was Australia’s hottest year on record on land, but was relatively cool in waters surrounding northern and western Australia, in part because of the influence of the Indian Ocean Dipole. This map uses the HadCRUT5 dataset.


Impacts of higher ocean temperatures

Rising sea surface temperatures have a range of impacts, including a greatly increased risk of marine heatwaves (see case study: Marine heat waves, in the Extreme weather events section in the Marine chapter). Marine heatwaves, along with more sustained increases in ocean temperatures, can lead to changes in the marine ecosystem – for example, changes in the range of species. One particularly visible impact of rising ocean temperatures is a greatly increased frequency of coral bleaching in the Great Barrier Reef (see case study: Climate change and the Great Barrier Reef), and other coastal waters in northern Australia.

Higher ocean temperatures will continue to impact Indigenous coastal communities’ traditional ecological knowledge and knowledge systems. The Kowanyama Community (Castillo 2009) participated in a Traditional Knowledge Initiative (United Nations University 2007) through the United Nations University, where they raised issues about ocean warming contributing to sea level rise and freshwater impacts. Sea level rise may also cause the intrusion of salt water into freshwater ecosystems; this will impact the way in which the Kowanyama people access their traditional knowledge. This fusion of waters leads to environmental changes that will impact traditional freshwater and saltwater plant and aquatic species. These types of impacts will be felt in all Indigenous coastal communities.

Indigenous communities exposed to rising ocean temperatures, such as the Malgana Traditional Owners in Shark Bay, Western Australia, have reported impacts on their traditional Country, and their ability to maintain cultural practices and protect the seagrass meadows. Increased sea surface temperatures (e.g. 2–5 °C above long-term averages during the heatwave in the summer of 2010–11), as well as increased ocean acidification and changing seawater chemistry, have impacted more than 1,300 square kilometres of dense seagrass meadows (Marine Biodiversity Hub 2020). This in turn affects the species that rely on seagrass meadows, which include dugongs, turtles, cormorants and bottlenose dolphins (Marine Biodiversity Hub 2020).

Case Study Climate change and the Great Barrier Reef

Climate change is the most significant threat to the long-term outlook for the Great Barrier Reef region (GBRMA 2019). Although ocean temperatures are only one of several influences that pose a threat to the Reef (others include tropical cyclones, freshwater plumes and nutrient run-off from floods on land, and pests such as the crown-of-thorns starfish), they show the most clear-cut long-term trend, which is expected to continue in the future.

High marine temperatures can cause ‘bleaching’, when corals expel the symbiotic algae (zooxanthellae) living in their tissues, causing the coral to turn white. If high temperatures persist (or if other pressures further stress already bleached corals), the coral dies. Mass coral bleaching is when entire tracts or regions of a reef bleach.

Before 2016, only 2 mass coral bleaching events had occurred in the Great Barrier Reef, in 1998 and 2002. Following the event of 2016 (reported in the 2016 state of the environment report), there have been further mass bleaching events in 2017 and 2020; the 2016 and 2017 events were the first instance of mass bleaching in consecutive years. All of these bleaching events occurred during periods of abnormally high sea surface temperatures in the region. The 2016 and 2017 events were focused primarily on the northern and central Reef, leaving the southern portion largely unaffected; conversely, the 2020 event had its worst impacts in the south. The 2020 event, however, has led to comparatively limited coral mortality, with the 2020–21 summer providing favourable conditions for short-term recovery.

Sea surface temperatures have been rising consistently in the Great Barrier Reef region (BOM 2021). In February, the hottest month of the year, sea surface temperatures in the region have warmed by about 1 °C from 1900 to 2020 (see Figure 7). February 2016 was the first month on record to have a regional mean temperature above 29 °C (compared with the long-term February average of 28.0 °C), but the 2016 value of 29.1 °C was surpassed by 29.2 °C in February 2020. These very high monthly mean temperatures were associated with prolonged marine heatwaves affecting large parts of the region.

Figure 7 February sea surface temperature anomaly (1961–90 baseline) averaged over the Great Barrier Reef region, 1900–2021

The most significant long-term decline in coral has been in the northern Great Barrier Reef (see case study: Australia’s changing reefs, in the Reef recovery and management section in the Marine chapter). Hard coral cover in this region was between 20% and 30% for most of the period from when records began in the early 1980s until 2015. There was then a sharp drop to a record low of 13% in 2017. There has been a minor recovery to 17% in 2020, and then a stronger recovery to 27% in 2021, supported by relatively favourable conditions for coral recovery in the summer of 2020–21, with no major marine heatwaves or severe cyclones. Hard coral cover on the central and southern Reef shows more variability between years, with both regions dropping to record lows of 11% in 2011 as a result of the impacts of severe tropical cyclones (Yasi in the central Reef, Hamish in the south) before a rapid rebound. The central Reef reached 29% hard coral cover in 2016 before a fall to 14% in 2019 and a rebound to 26% in 2021. Other studies have found a decline of more than 50% from the 1990s to the present in the number of small, medium and large corals on the Reef (Dietzel et al. 2020). However, corals acclimatised to some extent to marine heatwaves in 2016 and 2017 (Hughes et al. 2019) – less bleaching was found for a given warming threshold in 2017 than for the same amount of warming in 2016.

Rising ocean temperatures are not the only aspect of climate change with the potential to affect coral reefs. Coral can be adversely affected by ocean acidification and rising sea levels, although the former is so far likely to have had a negligible impact on coral compared with warming temperatures (GBRMA 2019). The occurrence of freshwater plumes, and associated input of sediments and nutrients (see the Marine chapter), from flooding of coastal rivers has been relatively frequent since the 1970s compared with the past 370 years as a whole (Lough et al. 2015), but, despite their severity on land, the floods in the Townsville region in early 2019 had only a minor impact on the Reef. Water quality in the Great Barrier Reef region is routinely reported by the Queensland Government through reef water quality report cards (DES 2021).

Tropical cyclones, such as Debbie in 2017 (see case study: Severe tropical cyclone Debbie, in the Tropical cyclones section in the Extreme events chapter) and Penny in 2019, have also impacted the Reef in the past few years, but there has not been a cyclone in the past 5 years on the scale of the category 5 systems Hamish (2009) and Yasi (2011).

Coral reefs are expected to continue to decline with further global warming. Projections reported by the Intergovernmental Panel on Climate Change (IPCC 2018) indicate that coral reefs are expected to decline globally by a further 70–90% (relative to 2015) at 1.5 °C global warming, and by more than 99% at 2 °C global warming. However, there are large regional differences, and the Great Barrier Reef has, to date, recovered more rapidly after bleaching events than the larger-scale average. It is expected that the total number of tropical cyclones in the region will remain stable or decline, but that a greater proportion of the cyclones that do occur will be intense. The occurrence of extreme rainfall on land is likely to increase, even though changes to total rainfall are unclear (GBRMA & CSIRO 2021).