Greenhouse gases

Increased concentrations of greenhouse gases in Earth’s atmosphere since the industrial period began have been the dominant driver of long-term climate change in Australia and globally. The Intergovernmental Panel on Climate Change (IPCC) has found that the level of anthropogenic warming (i.e. the amount of warming attributable to human activities) between 1850−1900 and 2010−19 was likely to have been in the range 0.8–1.3 °C, closely matching the observed warming of 1.06 °C over this period.

Quantification of the human contribution to warming is more challenging at the national scale than at the global scale, but it is clear that observed Australian warming is also predominantly due to human activity. There is also a high level of confidence about human influence on the observed rainfall decline in the south-west of Western Australia (IPCC 2021). Some of the changes that have been observed in other variables, such as decreased cool-season rainfall elsewhere in southern Australia and an increased frequency of dangerous fire weather, are also consistent with changes that would be expected with anthropogenic climate change, but attribution of observed changes has not yet been established to the same level of certainty as for temperature.

National greenhouse gas emissions

In general, Australian greenhouse gas emissions are falling.

Greenhouse gas emissions for Australia for the year to December 2020 were 499.0 megatonnes (Mt) of carbon dioxide equivalent (CO2-e), 26.1 Mt (5.0%) lower than in 2019 (Figure 16) (DISER 2020b). This is the lowest annual value since the National Greenhouse Gas Inventory was established in 1990. It is a decrease of 22.6% since the peak in the year ending June 2007, and a decrease of 5.7% since 2000.

However, the low 2020 value in part reflects reductions in emissions due to the COVID-19 pandemic, which are expected to be temporary (see case study: COVID-19, greenhouse gas emissions and climate). In particular, emissions from transport decreased 12.1% (12.0 Mt CO2-e) from the previous year. Before the onset of the pandemic, emissions had been relatively stable from 2013 to 2019, with all annual values in the range 523–540 Mt CO2-e.

Figure 16 Quarterly greenhouse gas emissions for Australia, December 2000 to December 2020

Contributions to emissions vary across sectors (Figures 17 and 18). In 2020, 33.6% of total emissions nationally were from the electricity sector, making it the largest single contributor to emissions nationally. Emissions from the electricity sector have generally been declining since 2009 (apart from a brief period of increase from 2013 to 2015), largely because of an increasing share of renewables in electricity generation and a consequent decrease in the share of other forms of power generation, particularly coal. In 2019, 20.9% of electricity in Australia was generated from renewable sources, with wind and solar energy both playing an increasing role. This compares with values in the range 7–10%, mostly from hydro-electricity, in most years from 2000 to 2010 (DISER 2021). This outcome is consistent with target 7.2 of the United Nations Sustainable Development Goals (By 2030, increase substantially the share of renewable energy in the global energy mix).

The contributions to emissions by sector vary considerably in different parts of the country, driven by factors such as the proportion of renewables in local electricity generation, local land use and the mix of local economic activity. For example, in Tasmania, where most electricity generation is from zero-emissions sources, transport forms the largest share of emissions.

Major sectors in which emissions have continued to grow have been transport, fugitive emissions, and stationary energy excluding electricity, although the 2 former categories experienced sharp falls in emissions in 2020. A major factor in the 2 latter categories has been the growth in liquefied natural gas production and export since 2015, and associated flaring. Transport-related emissions have grown steadily; petrol use has been stable since 2010, but diesel use continues to increase because use of light commercial vehicles (LCVs) has grown more rapidly than use of passenger vehicles. LCVs made up 18.8% of total vehicle-kilometres travelled in 2012, increasing to 20.5% in 2018 and 21.9% in 2020 (ABS 2020). Agricultural emissions have been fairly stable over most of the past decade but can fluctuate with stock numbers, and crop type and area. Agricultural emissions were relatively low in 2019–20, due primarily to destocking during the 2017−19 drought (see the Land chapter).

Figure 17 Contributions by sector to Australian greenhouse gas emissions, 2020

Figure 18 Greenhouse gas emissions by sector, expressed as a change from 1990

A major factor in reducing Australian emissions has been the land use, land-use change and forestry (LULUCF) sector (see the Land chapter). The LULUCF sector was a major source of emissions in the 1990s, contributing more than 150 Mt CO2-e in 1990 and 1991. These emissions declined substantially by 2000, and by 2015 the LULUCF sector had become a net sink in Australia, contributing −24.5 Mt CO2-e in the year to December 2020. Regrowth of forest, much of it on previously cleared land, is a major contributor to this. The total area of forest in Australia, which decreased from about 138 million hectares in 1990 to 134 million hectares in 2007−08, has increased again, to reach near 1990 levels in 2018. Forest clearing is still a contributor to emissions, accounting for 40–50 Mt CO2-e in most years since 2010, but is offset by land being converted to forest, and uptake of emissions by land that has remained forest (e.g. plantations regrowing after harvesting). Most clearing is of regrowth; only 9% of forest clearing is of previously uncleared land (primarily for agriculture or urban development).

Land-use change, although currently a net sink in Australia, contributed a net 6 gigatonnes (Gt) globally to emissions in 2020; major contributors were deforestation (primarily in tropical regions), offset by regrowth on abandoned agricultural land. Land and ocean sinks take up just over half of global emissions; in 2020, oceans took up 9.2 Gt (which contributes to ocean acidification) and land areas 12.5 Gt. The land sink is highly variable from year to year, with variations of up to 3 Gt between years.

Bushfires can be associated with very large quantities of emissions, as well as substantial uptake of emissions from regrowth in the following years. Initial estimates indicate that bushfires in temperate forests in Australia in the 2019−20 season generated a net 830 Mt CO2-e in emissions, or approximately 1.6 years worth of ‘normal’ emissions. However, it is expected that the vast majority of these emissions will be absorbed by regrowth of the burnt areas; analysis following the 2002−03 fires in the Australian Alps found that 96% of the emissions had been absorbed within 10 years (DISER 2020a).

Irregular bushfires in temperate forests are considered to be ‘natural disturbances’ under IPCC guidelines. Hence, their emissions and uptake from postfire regrowth are excluded from standard national accounts, except where they lead to an ongoing change in land use or land cover (although they are still reported on separately). One example of such an ongoing change is the conversion of some former plantation forests, which were not replanted after the 2003 fires, to urban development in Canberra.

In a normal year, the bulk of bushfire-related emissions in Australia occur as a result of seasonal burning in tropical savanna areas of northern Australia. In these regions, emissions from burning and uptake from regrowth are normally approximately in balance in any given year.

  • Globally, CO2 emissions from fossil sources are estimated to have fallen by 7% in 2020 (Friedlingstein et al. 2020), to approximately 34 Gt. The 2019 value of 36.4 Gt was only 0.1% higher than that of 2018, indicating some level of stabilisation before the COVID-19 pandemic. Total global emissions in 2020, including land-use change, were approximately 40 Gt. This means that Australian emissions are approximately 1.2% of global emissions, a slight decline in recent years; however, Australia remains among the world’s largest per-person emitters.

State and territory emissions

At a state and territory level (DISER 2019), emissions decreased from 2005 to 2019 in all jurisdictions except Western Australia and the Northern Territory (see Greenhouse gas emissions reduction), which are both major exporters of liquefied natural gas and have seen other emissions increases as a result of expansion of the resources sector.

The LULUCF sector has become a net sink in most jurisdictions. In Tasmania, which already had relatively low per-person emissions from fossil fuel sources (partly due to the lack of emissions from the electricity sector) and hence had changes in emissions that were historically dominated by LULUCF, LULUCF shifted from 2005 to 2019 from being a large net source to a large net sink, sufficient to offset all remaining emissions in the state. This is in part due to reductions in native forest harvesting. South Australia has also seen a sharp increase in the uptake of emissions from the LULUCF sector in the past 10 years compared with 2005 levels. The LULUCF sector is still a net source in Queensland, but to a much lesser extent than in 2005.

State and territory data reported here are from state and territory inventories to 2018 published by the Australian Government. These may vary from data reported by those jurisdictions because of differences in definitions (e.g. the Australian Government reports Australian Capital Territory, or ACT, electricity emissions data only for electricity generated within the ACT, whereas the ACT Government reports for electricity consumed within the ACT, most of which is generated outside the ACT).

Assessment Greenhouse gas emissions in Australia
2021
2021 Assessment graphic showing that pressures are high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation is stable.
Adequate confidence
2016
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.
2011
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.

Greenhouse gas emissions in Australia have decreased substantially from their 2007 peak, largely due to the land use, land-use change and forestry sector, which has changed from being a net source to a net sink, and the increase in the proportion of Australian electricity generated from renewable sources. Emissions in other sectors, particularly transport, stationary energy and fugitive emissions, have increased. Emissions were relatively stable from 2013 to 2019 before a sharp fall in 2020, some of which was due to the COVID-19 pandemic and is likely to be temporary.
It is unclear whether the further fall in emissions required for Australia to meet its nationally determined contribution under the Paris Agreement (a 26–28% decrease on 2005 levels by 2030) will occur.
Related to United Nations Sustainable Development Goal targets 7.2, 13.2

Atmospheric concentrations

Concentrations of greenhouse gases in the atmosphere have continued to increase over recent years. The major greenhouse gases are carbon dioxide (CO2), methane and nitrous oxide, which account for about 64%, 19% and 6%, respectively, of changes in radiative forcing since 1750.

The concentrations of greenhouse gases in the atmosphere will continue to increase over the next 20–30 years under any plausible global emissions scenario. Beyond that point, concentrations are highly sensitive to the extent to which emissions are reduced at a global scale. A scenario in which global net zero emissions were achieved by 2050 would see CO2 concentrations likely peak near or below 450 parts per million (ppm) in mid-century; conversely, under a high-range emissions scenario, CO2 concentrations would continue to increase, to reach projected levels exceeding 1,000 ppm by 2100 (Gidden et al. 2019).

The most recent comprehensive globally averaged data on greenhouse gas concentrations is for 2020. In 2020, the globally averaged concentration (mole fraction) of CO2 was 413.2 ppm, an increase of 2.5 ppm from the 2019 value and 13.2 ppm from 2015. The rate of increase has been 2–3 ppm per year in most years since the early 2000s, with larger increases in major El Niño years such as 2016. The globally averaged concentration of methane in 2020 was 1,889 parts per billion (ppb), an increase from 1,845 ppb in 2015. The globally averaged concentration of nitrous oxide was 333.2 ppb in 2020, compared with 328.0 ppb in 2015.

More recent information is available from individual locations, such as the Kennaook/Cape Grim Baseline Air Pollution Station (BAPS) in north-western Tasmania, operated by CSIRO and the Bureau of Meteorology. It is one of 3 locations globally recognised as a BAPS by the World Meteorological Organization (WMO) and is one of 3 cornerstone global observatories in the WMO Global Atmosphere Watch Programme. As greenhouse gas levels have a seasonal cycle (which varies from location to location), data from individual locations are best compared either as annual averages or with data from the same time of year in previous years. Absolute concentrations of greenhouse gases at Kennaook/Cape Grim are slightly below global averages, but the rate of change is similar (Figure 19). In July 2021, the concentration of CO2 at Kennaook/Cape Grim was 412.1 ppm (compared with 401.3 ppm in July 2016), of methane 1,851.2 ppb (1,802.2 ppb in July 2016) and of nitrous oxide 333.2 ppb (327.7 ppb in July 2016).

An Aggregated Greenhouse Gas Index calculated from Kennaook/Cape Grim observations, which combines the radiative effect of all greenhouse gases (including trace greenhouse gases), shows a 2020 value of 148% of 1990 levels, compared with 139% in 2015.

Figure 19 Annual mean concentrations and year-on-year changes in the concentrations of (a and b) carbon dioxide, (c and d) methane and (e and f) nitrous oxide measured at Kennaook/Cape Grim

Case Study COVID-19, greenhouse gas emissions and climate

The COVID-19 pandemic led to widespread shutdowns of activity in Australia and elsewhere during 2020. This contributed to sharp reductions in greenhouse gas emissions in most countries, as well as reduced emissions of other substances.

Preliminary estimates indicate that global greenhouse gas emissions arising from the consumption of fossil fuels in 2020 decreased by 7% from 2019 values (Friedlingstein et al. 2020). At the peak of global shutdowns in early April 2020, estimated reductions in global greenhouse gas emissions were 17% (about half from surface transport), and individual countries had peak reductions of 26% (Le Quere et al. 2020).

In Australia, reductions in emissions were slightly below the global average. There was a 5.0% decrease for 2020 compared with 2019, with the June and September quarters 6–8% below the corresponding quarters of 2019. This reflects the fact that, outside Victoria, COVID-19-related restrictions on activity in Australia in 2020 were less severe and prolonged than in many other countries.

The largest sectoral decrease was 12.1% for transport, including 11.5% from petrol consumption and 50.9% from jet fuel (Figure 20).

Figure 20 Changes from 2019 to 2020 in Australian greenhouse gas emissions, by sector

Source: DISER (2020b)

Not all the reduced emissions in 2020 were related to the pandemic – for example, there was a 2.5% decrease in agricultural emissions between 2018–19 and 2019–20, which largely reflects the impacts of drought conditions during 2019. Agricultural emissions increased again in the second half of 2020, with the year to December 2020 having no change from the year to December 2019. Emissions from electricity generation were down by 4.9%, but this largely reflects an increased share of renewable energy, with only small changes in total electricity demand.

At a global scale, the impact of 2020’s reduced emissions on temperatures is expected to be negligible. Modelling has found that the reduced emissions are expected to lead to cooling of 0.01 °C (±0.005 °C) by 2030 relative to a scenario where they did not occur (Forster et al. 2020). In the short term, the pandemic led to slight increases in global temperatures during 2020 (Gettelman et al. 2020), as reduced emissions of aerosols and particulates more than offset reduced greenhouse gas emissions (particularly in heavily industrialised land areas of the Northern Hemisphere). However, these aerosol effects are expected to be short-lived compared with the ongoing impacts of changes in greenhouse gas emissions.