Clear differences between countries regarding the time needed to achieve net-zero emissions

The researchers used 1.5 °C and 2 °C scenarios from Integrated Assessment Models to analyse in which year ten large countries would need to bring emissions to net-zero if they are to achieve the targets of the Paris Agreement. Targets typically focus on net-zero, implying that carbon dioxide removal from the atmosphere (e.g. via afforestation) can be allowed to offset emissions in other sectors that are hard to reduce.

In the article, the researchers describe the factors that could explain the differences between these countries. Most of the scenarios focus on cost-effectiveness - reducing global emission levels at the lowest possible cost, i.e. with a cost-optimal distribution of reductions across countries.

CO₂ storage potential and afforestation are important factors

Under a scenario that keeps the increase of global mean temperature well-below 2 °C, globally, net-zero emissions will be achieved shortly after 2080; under a 1.5 °C temperature increase constraint, this moment will be sooner, somewhere between 2050 and 2070. Under the scenarios based on cost-optimal implementation, Brazil and the United States could achieve net-zero emissions sooner than the global average, while for India and Indonesia this may be later. China, Russia and the European Union are relatively close to the global average. Explanatory factors for the year in which countries achieve net zero-emissions are their capacity to reduce emissions (e.g. CCS and afforestation potential and share of non-CO₂ emissions) and their development stage.

Equity considerations

Cost-effectiveness is only one aspect of national target-setting. Equity also plays a role. In an equity-based distribution (e.g. based on national carrying capacity, historical responsibility or per capita emissions), wealthier countries and regions should phase out their emissions sooner than in a situation of cost-optimal distribution. This applies to Canada and the European Union, as well as to China. Brazil and India would be allowed to phase out later, as would countries with lower per-capita emission levels and emerging economies. Phasing-out efforts in these countries could be supported by the wealthier countries, as is expressed in the Paris Agreement’s description of 'common but differentiated responsibilities'.

Updating national targets

This study can be seen as a first step to inform setting net-zero emissions targets. However, national models or other tools will need to be applied to incorporate relevant domestic circumstances fully. Another critical point is that the scenarios used were created in 2016–2018.

Within the Paris Agreement framework, countries are required to regularly update their targets and communicate them in the form of Nationally Determined Contributions. This information can then be used to assess if they are likely to achieve the Paris targets or whether ambitions need to be increased. This process is now underway and will be completed in 2023. Preferably, countries should clearly define whether their target refers only to CO₂ or includes all greenhouse gases, as well as the extent to which they intend to use the capacity for removing CO₂ from the air (e.g. through reforestation and the use of bioenergy in combination with carbon capture and storage). It is also important that they clarify how they will incorporate considerations of equity into their policies.