Regional net zero emission goals strongly depend on the allocation of negative emissions and effort-sharing

Greenhouse gas neutrality targets attractive – but will require further elaboration

These are the main findings in the report Global and Regional Greenhouse Gas Emissions Neutrality. Implications of 1.5 °C and 2 °C scenarios for reaching net zero greenhouse gas emissions. In this report, researchers from PBL Netherlands Environmental Assessment Agency give an overview of the literature on greenhouse gas emissions neutrality, here defined as reducing global emissions of all greenhouse gases to net zero. The report discusses existing scenarios from integrated assessment models (IAMs), focusing on achieving the 2 °C objective, and on global as well as regional decarbonisation implications of phasing out greenhouse gas emissions.

Paris emissions neutrality goals

The issue of greenhouse gas neutrality as indicated in the Paris Agreement is increasingly gaining interest among policymakers. One advantage is that it provides a clear formulation of the long-term ambition of climate policy. However, key questions need to be addressed before the concept could be used. The Paris Agreement is aimed to keeping global warming to well below 2 °C and to pursue efforts to limit it further, to 1.5 °C. These targets, in themselves, do not provide any guidance for policymakers and investors about how to achieve them. Therefore, negotiators also agreed on operational emission goals, such as the aim of greenhouse gas emissions peaking as soon as possible, or setting emission targets for a particular year. Recently, policymakers started to focus on the concept of reaching zero net greenhouse gas emissions (i.e. neutrality) in a particular year. This concept provides a clear long-term goal and is consistent with the Paris Agreement on achieving a ‘balance between anthropogenic emissions by sources and removal by sinks of greenhouse gases in the second half of this century’.

Emission targets based on the scenario database

The 2 °C scenarios show that global greenhouse gas emissions are projected to reach net zero between 2080 and 2100, and for CO₂, this will be between 2055 and 2070. Under globally cost-optimal scenarios, greenhouse gas emissions neutrality is reached by 2100 in China and the EU, and by 2065 in the United States, while carbon neutrality (CO₂ only) is reached earlier. These figures, however, cannot be directly used in policy-making. Targets will be set not only on the basis of costs, but also on other considerations. Earlier studies based on equity calculations, for example, found that greenhouse gas emissions neutrality by 2070 could be a logical target for the EU for achieving the 2 °C objective. Moreover, it is not yet clear how negative emissions need to be accounted for on a regional level.

The allocation of negative emissions

Greenhouse gas emissions neutrality does not imply full decarbonisation, as remaining emissions can be compensated for by negative emissions from LULUCF sinks and through biomass used in energy production coupled with carbon capture and storage (BECCS). Therefore, regions with a large potential for negative emissions show earlier phase-out years, although the allocation of negative emissions to either the biomass-producing region or the region applying it with CCS does influence regional phase-out projections. Effort-sharing studies that have calculated emission allowances by applying different equity principles to global emissions pathways consistent with achieving 2 °C or 1.5 °C, show even larger reduction targets for OECD countries, including those in the EU.