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Human activities create carbon dioxide and other greenhouse gases, which are emitted into the air.

Scientists know that the source of extra carbon dioxide in the atmosphere is industrial activity because analysis of the different types (or isotopes) of carbon shows that it comes from human activities, predominantly the burning of fossil fuels to generate electricity.

The carbon cycle

The extra carbon from human activities is changing the natural cycling of carbon through the environment that has occurred for millions of years.

Carbon flows in and out of the land, ocean and living things as part of the carbon cycle. Plants take in carbon dioxide during photosynthesis, with animals – including humans – breathing it out.

When plants and animals die, their stored carbon is released as carbon dioxide into the air.

Each year, natural processes such as respiration and decay, forest fires and volcanic eruptions add 190.2 billion tonnes of carbon to the air. This is balanced by the oceans, land and plants absorbing 190.2 billion tonnes of carbon from the air.

People create carbon dioxide when we burn fossil fuels such as gas, petrol, oil, and coal, adding an additional 9.1 billion tonnes of carbon to the air each year.

Plants and the land take up 2.8 billion tonnes of this extra carbon, while the oceans take up 2.2 billion tonnes.

The remainder (4.1 billion tonnes) stays in the air, increasing the atmospheric concentration of carbon dioxide.

Global emissions

Emissions of carbon from fossil fuels make the largest contribution to climate change. About 90 per cent of the world’s carbon emissions comes from the burning of fossil fuels – mainly for electricity, heat and transport.

In 2021, most of the world's fossil fuel carbon emissions came from coal (40 per cent), oil (32 per cent), natural gas (21 per cent), cement (5 per cent) and flaring and other smaller sources (2 per cent).

Just four regions accounted for about two-thirds of global fossil-fuel carbon emissions in 2021: China (31 per cent), the USA (14 per cent), the EU27; 7 per cent), and India (7 per cent).

Industrialised countries represent just 20 per cent of the world’s population but account for 80 per cent of cumulative carbon dioxide emissions since the beginning of the industrial revolution.

Eraring coal-fired power station in Newcastle. ©  Credit: Nick Pitsas

Australian emissions

Australia is the world’s 14th highest emitter, contributing just over 1 per cent of global emissions.

The Australian Government tracks the nation’s greenhouse gases emissions through the National Greenhouse Gas Inventory. According to the December 2020 update, Australia emitted 499 million tonnes of carbon dioxide equivalent, a 5 per cent decrease on 2019.

Energy production is the largest contributor to Australia’s carbon emissions. This is followed by transport, agriculture, and industrial processes. Specifically:

  • energy (burning fossil fuels to produce electricity) contributed 33.6 per cent of the total emissions
  • stationary energy (including manufacturing, mining, residential and commercial fuel use) 20.4 per cent
  • transport 17.6 per cent
  • agriculture 14.6 per cent
  • fugitive emissions 10.0 per cent
  • industrial processes 6.2 per cent
  • waste 2.7 per cent.

Greenhouse gas emissions are also influenced by changes in land use. Total (or net) greenhouse gas emissions factor in the influence of how land is used.

For example, reductions in forest clearing increase the carbon stored in plants and trees rather than in the atmosphere, reducing net emissions.

Australia’s greenhouse gas emissions total was reduced as a result of land use, land use change and forestry removing 4.9 per cent of our emissions in 2020.

Resulting concentrations

As a result of increasing emissions, the global atmospheric carbon dioxide concentration has increased by 48 per cent since pre-industrial times, rising from 277 ppm in 1750 to 412 ppm in 2020.

The carbon dioxide concentration today is much higher than the natural range of 172 to 300 ppm that existed for hundreds of thousands of years.

In fact, carbon dioxide concentrations now are likely to be the highest they have been in at least the past 2 million years.

It's expected a total of 39.7 billion tons of carbon will be emitted by the end of 2021.

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