The OECD’s Air and GHG emissions indicator defines greenhouse gases as the sum of seven gases with direct effects on climate change and reports total emissions excluding land use, land-use change and forestry (LULUCF) in thousand tonnes of CO2-equivalent. This is the OECD’s primary data framework for cross-country greenhouse-gas comparisons, including per-capita calculations when combined with population data.

Australia had the highest per capita greenhouse gas emissions of all OECD member countries in 2023, at 22 metric tons of carbon dioxide equivalent (tCO2e) per person. Canada was second with just over 20 tCO2e per person.

In 2018, greenhouse gas emissions per capita in Australia were 22.4 tCO2e/capita. The OECD average in 2018 was 11.5 tCO2e/capita. These values are presented as "2018 OECD average: 11.5 tCO2e/capita. 2018 Australian average: 22.4 tCO2e/capita." in the country note for Australia.

The OECD environment statistics dataset "Greenhouse gas emissions by source" (DataSetCode=AIR_GHG) contains indicators for greenhouse gas emissions based on production and includes per capita measures. The data are compiled from "National Inventory Submissions to the United Nations Framework Convention on Climate Change (UNFCCC)" and other official sources. This dataset underlies derived charts such as per-capita greenhouse gas emissions by country in tonnes of CO2 equivalent. Users can select variables including total greenhouse gas emissions and divide by population to obtain per-capita values for individual OECD countries such as Australia.

Greenhouse gas emissions are measured in tonnes of carbon dioxide-equivalents per person, and these figures reflect territorial emissions. The Australia profile states that per capita greenhouse gas emissions are shown as the sum of all greenhouse gases, measured in carbon dioxide equivalents.

For 2023, Australia is listed at 14.02 metric tons of carbon dioxide equivalent per capita in the OECD ranking shown here, with Canada at 14.35 and the United States at 13.9. This source uses a CO2-emissions indicator rather than the full greenhouse-gas metric, so it is relevant only as a comparison point and not a direct match to the claim.

The OECD "Greenhouse gas footprint indicators" dataset provides production and demand‑based greenhouse gas emissions per capita for 76 economies from 1995 to 2020. The indicators include "production and demand-based emissions per capita" expressed in tonnes of CO2 equivalent, allowing comparison of per‑capita greenhouse gas emissions across OECD members. Australia is among the economies covered in the dataset for the period 1995–2020.

According to 2020 figures from Our World in Data – the most recently available per capita data – each person in Australia emits 15.4 tonnes of CO2 annually. Despite managing to reduce its per capita emissions, Australia now sits at 11th place compared to all other nations, higher than its previous ranking of 13th place in 2019. But when ranked among countries that are members of the Organisation for Economic Co-operation and Development (OECD) – a group of 38 nations generally regarded as being developed and high-income – Australia ranks first as the bloc’s highest emitter per capita.

The study reports that Australia's energy-related CO2 emissions per capita are significantly higher than the OECD average. It also states that Australia's total emissions per unit of output are very high by OECD standards.

A study on "Convergence of CO2 emissions in OECD countries" using Global Carbon Project data for 1960–2018 finds that Australia and Canada are among the biggest per‑capita emitters, along with the US and Luxembourg. The analysis focuses on CO2 per capita by OECD country and reports that these countries consistently have high per‑capita emissions relative to other OECD members. The dataset used provides gross carbon emission data per capita for 30 OECD countries over the period 1960–2018.

For 2014, the chart lists Australia at 22.239 tonnes per capita for total greenhouse gas emissions per capita in OECD countries. That is above the 20 tCO2e threshold named in the claim, although it is an older snapshot rather than a current OECD release.

An online discussion of "Total greenhouse gas emissions per capita in OECD countries" notes that Australian emissions are significantly higher—about three times the global average and above the OECD average. The post states that "Our emissions levels are the highest among OECD nations" when measured on a per‑capita basis. The discussion references OECD environment statistics charts showing Australia at the top of per‑capita greenhouse gas emissions rankings among OECD members.

The Wikipedia entry "List of countries by carbon dioxide emissions per capita" reports that Australia’s CO2 emissions per capita were 14.21 tonnes in one recent year, with earlier values such as 18.56 and 19.143 tonnes in prior years. The table shows Australia as a high per‑capita emitter compared to the world average, with notes indicating Australia is an "exporter" of fossil fuels. The historical series indicates that Australia’s per‑capita CO2 emissions have exceeded 14–19 tonnes in several years.

One chart of "Total greenhouse gas emissions per capita in OECD countries" shows Australia at 22.24 tonnes per capita, USA at 21.55 and Canada at 20.51 tonnes per capita for the year 2014. This chart is described as using data from the "OECD Environment Statistics: Greenhouse gas emissions by source 2016" dataset. The figures illustrate that Australia’s per‑capita greenhouse gas emissions exceed 20 tonnes CO2 equivalent and are the highest among the OECD countries listed.

This page says Australia has one of the highest carbon footprints per person, citing 17 tons a year, which is not an OECD dataset and uses carbon footprint framing rather than OECD greenhouse-gas per-capita data.