気候変動：パリ協定を達成するために、CO2の受動的吸収を計算から分離する

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.