Geological Net Zero and the need for disaggregated accounting for carbon sinks
This week, we take a closer look at the paper that has been accepted for publication in Nature. The study was led by Myles R. Allen, from the Department of Physics of the University of Oxford, in the UK.
In this paper, the authors discuss how crucial the boundaries we use to define what constitutes anthropogenic CO2 removals are, and the risks associated with leaving free room for the interpretation of such definition to different stakeholders. In particular, the authors warn about the risks of allowing “passive” CO2 uptake, such as enhanced vegetation growth due to CO2 fertilization, to be included as removals when we discuss net anthropogenic emissions goals.
The definition of removals used in the IPCC Scientific Assessments explicitly “excludes natural CO2 uptake not directly caused by human activities”. Scenarios in which global CO2 emissions are reduced to net zero by 2050 and removals are identified based on the IPCC definition, ensure CO2 concentration gradual decrease, hence global temperature stabilization, according to the Paris Agreement objectives. Progressively re-classifying all “passive” CO2 uptake as anthropogenic removal, to be used to offset ongoing CO2 emissions, allows for avoiding actual emission reductions or active removals, leaving some anthropogenic emissions unabated. Scenarios in which this alternative definition is used show that this will lead to CO2 concentration stabilization only, which ultimately delays by many centuries the chance to halt global warming, missing the objectives set by the Paris Agreement.
Here is a recap of the main takeaways from this study:
- CO2 emissions will continue to drive warming until fully balanced by active anthropogenic CO2 removals.
- While explicitly excluded from the IPCC definition, for practical reasons, many greenhouse gas accounting systems allow some “passive” CO2 uptake to be included as removals in the definition of net anthropogenic emissions.
- Including passive CO2 uptake among removals will undermine the Paris Agreement, as nominal net zero emissions would not halt global warming.
- To address this problem, land management categories should be disaggregated in emissions reporting and targets to better separate the role of passive CO2 uptake.
- Policy targets should acknowledge the need for Geological Net Zero, meaning one tonne of CO2 permanently restored geologically for every tonne still generated from fossil sources.
Read the full paper here: Geological Net Zero and the need for disaggregated accounting for carbon sinks