What is a fair carbon budget for Australia?

During the continuing debate over whether Australia will meet its Paris target for greenhouse gas (GHG) emissions (see Skarbeck and Blakers) and the accounting trick by which they are trying to achieve it, little attention has been given to the target that Australia should set, based on climate science and ethics. Specifically, what is Australia’s fair share of the dwindling global carbon budget?

We cannot burn all Earth’s fossil fuel resources without causing a huge increase in global average temperatures and disastrous impacts. Limiting global heating to a particular temperature demands strictly limiting the total amount of global carbon emissions between now and the end of the century. This dwindling amount is the global carbon budget for that temperature.

Scientists have different ways of calculating these budgets. From intermediate values obtained from Carbon Brief and updated to the end of 2019, we take the budgets for heating with a 66% probability of less than 2ºC and 1.5ºC to be 1100 and 340 gigatonnes (Gt) of CO₂ respectively. Varying these numbers within expected ranges does not change the ethical implications discussed below.

We have focused on CO₂ because it is the principal GHG and because there are large uncertainties about some of the other GHGs. Recent global annual CO₂ emissions are estimated to be 37.5 Gt, while estimates of annual emissions from all GHGs vary between 47 and 55 Gt of CO₂-equivalent. The global CO₂ budgets for 2ºC and 1.5ºC are equivalent to 29 and 9 years of emissions at current levels of emissions – however, global emissions are increasing.

Australia’s share of this global budget can be calculated in different ways, each having different ethical implications. One way is ‘grandfathering’, that is, assuming that Australia’s budget is determined by its current share of emissions.

According to official figures, Australia’s CO₂ emissions in 2017 were 381 Mt, about 1% of global CO₂ emissions. Hence grandfathering gives Australia CO₂ budgets of 11 and 3.4 Gt for 2ºC and 1.5ºC respectively from the beginning of 2020, corresponding to 29 and 9 years of current emissions, respectively.

But grandfathering our emissions is unfair to the inhabitants of other countries, because Australia has one of the highest per capita emissions in the world. Incidentally, the federal government emphasizes that our per capita emissions are declining, but this is mainly the result of Australia’s very high rate of population growth of 1.7%, third highest in the OECD, not from declining emissions.

A much fairer distribution of the remaining global carbon budget would be to allocate each person in the world an equal amount of emissions. This is consistent with the Universal Declaration of Human Rights.

This would give each person on the planet a remaining CO₂ emission budget of 44 tonnes from 1 January 2020. The average Australian is responsible for 15 tonnes of CO₂ emission per year. To avoid giving an incentive to population growth, the allocation should be made at a fixed time and not be increased with increasing population.

This approach, which is basic social equity, is also known as Contraction and Convergence. On this basis, Australia would receive only 0.33% of global CO₂ emissions, giving us 3.6 and 1.1 Gt, or 9 and 3 years of current emissions, for the 2ºC and 1.5ºC targets respectively.

Assuming a linear reduction of emissions to zero, the 2ºC target gives us 19 years with an annual emission reduction of 20 Mt, while the 1.5ºC target gives us 6 years with an annual emission reduction of 67 Mt.

In other words, if Australian governments were serious about the 1.5ºC target and respected the ethical principle that every person on the planet has equal rights, then we Australians would have to reach zero net emissions by the end of 2025. It’s not surprising that Contraction and Convergence receives no discussion from the representatives of Australia or other rich countries in international climate meetings.

Instead, the major political parties in Australia argue about which government had the most increases in GHG emissions under their respective reigns. At least that issue is easily fact checked. In Figure 1, the blue curve shows the time trend of Australia’s total CO₂-equivalent emissions and the green curve shows emissions excluding land use and land use change and forestry (LULUCF), from 1990 to 2017, based on the National Inventory Report (2019 version, Volume 2, Table 10.3). Neither of these curves includes emissions from wildfires. We have indicated the periods of reigning federal governments.

Figure 1 Comparison of Australian Government mitigation policy effectiveness on total GHG emissions, 1990-2016

Figure 1 gives total GHG emissions, which reached 530 Mt CO₂-equivalent in 2016, compared with 381 Mt of CO₂emissions. The difference is mainly the result of methane emissions from cattle, sheep, coalmines, and oil and gas fields.

Note how the inclusion of LULUCF gives a big reduction in total emissions from 1990 to 1995. Both curves rise from 1995 to 2007 under the Coalition. Then under Labor (2007-2013) the total curve declines and the non-LULUCF curve levels out and then declines. The carbon tax commenced in mid-2012. Its removal in mid-2014, following a change of government, resulted in an increase in non-LULUCF emissions.

So far, the biggest reduction in total emissions from 2005 towards the Paris target occurred under federal Labor, but it cannot claim much credit for this, which resulted mostly from reductions in LULUCF, a state responsibility.

Clearly, while total emissions were generally slightly lower under Labor, neither of the governments has done enough of substance towards reducing Australia’s emissions towards a fair share of the global carbon budget.

Mark Diesendorf and Dennys Angove School of Humanities & Languages, UNSW Sydney.