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Climate change: Separate passive CO2 uptake from calculations to meet the Paris Agreement
The temperature goals of the Paris Agreement may not be met if passive CO2 uptake is counted as a removal when calculating total anthropogenic emissions, a Perspective in Nature suggests. The Perspective also argues that all entities committed to the long-term temperature limit of the Paris Agreement need to plan to jointly achieve global Geological Net Zero.
CO2 emissions will continue to drive global warming until they are balanced by active removal. The definition of removal used by the assessment reports of the Intergovernmental Panel on Climate Change explicitly excludes the inclusion of natural uptake of CO2 not directly caused by human activities in its assessment of anthropogenic CO2 removals. However, many other reporting systems, including national greenhouse gas inventories, allow passive uptake — absorption of CO2 by natural systems, such as forests — to be included as a removal if it takes place on ‘managed land’ (which countries self-determine).
Myles Allen and colleagues argue that the goals of the Paris Agreement may not be met if passive uptake is allowed to be counted when calculating CO2 removals. They indicate that counting passive uptake as a removal will slow down global warming rather than halting it. The authors propose that land management categories should be disaggregated in emission reporting and targets to better separate account for the role of passive uptake. They also suggest that, wherever possible, any claimed removals should be in addition to passive uptake and propose a new mechanism for allocating resources to the protection of passive carbon sinks.
Additionally, Allen and co-authors propose that future targets to limit CO2 emissions should account for the need to reach Geological Net Zero, where for every tonne of CO2 generated by fossil fuel sources, another tonne is permanently restored to the solid earth. They suggest that, in addition to reducing emissions, 10% of any CO2 emissions still generated needs to be stored geologically by the mid-2030s with investment needed now for a further ten-fold increase in this stored fraction over the following 20 years. Although ambitious, the authors argue that this is achievable.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Professor Dave Frame, School of Physical & Chemical Sciences, University of Canterbury; and co-author of this research
The key idea behind "net zero" emissions is that net zero CO2 emissions is required to halt further climate change.
When we first wrote the papers on this idea (2009) we relied on the fact that forests (/etc) get more hungry for carbon as the atmosphere gets more CO2 in it.
Subsequent carbon accounting practices have in some cases counted natural sinks of CO2, when the science behind net zero reasoning assumed they did not, unless they were additional to the carbon already being drawn down.
This leaves us in the undesirable position that some countries may claim to be "net zero" while continuing to contribute to warming, thus undermining the whole idea of net zero in the first place.
We need to improve the way we think about carbon accounting, and to rely less on the biosphere.
Ultimately the sort of net zero that we need to achieve is geological net zero: any CO2 that comes out of fossil reservoirs needs to be balanced by CO2 going back into geological stores.
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