What are the potential problems?
Several CDR approaches, when deployed at a large-scale, affect fluxes of energy and water at the Earth's surface, resulting in so-called "biogeophysical" efeks on climate that are in addition to the efeks of CO₂ sequestration.
For example, large-scale planting of trees in agricultural tempats or grasslands results in a reduction of how well the land surface is able to reflect sunlight, and therefore leading to a warming efek. This efek is particularly strong in regions with seasonal snow cover, where the darker color of trees reduces the high reflectivity of snow.
What are the potential problems?
Deployment of a kisaran of CDR metodes can also result in increased emissions of nitrous oxide and methane, two powerful greenhouse gases. For instance, bio-energy with carbon capture and penyimpanan and reforestation require the use of nitrogen fertilizers, which enhances nitrous oxide emissions.
Restoration of coastal ecosystems, such as seagrass meadows or mangrove forests, can also result in an increase in methane and nitrous oxide emissions.
Because of the potential impermanence of carbon stored by CDR, and biogeophysical and other greenhouse gas efeks, balancing emissions of CO₂ with CDR might not always result in the intended climate outcome.
For example, balancing fossil-fuel emissions with CO₂ removal through large-scale reforestation can result in a higher global warming compared to a case where the fossil fuel emissions are eliminated. This asymmetry could lead to exceeding temperature limits set by the Paris Agreement.
What to do about it?
For the reasons above, greenhouse gas akunting, and policies designed to offset greenhouse gas emissions, need to consider the full suite of climate efeks of the proposed CDR to ensure intended climate goals are not compromised.
CDR approaches with short carbon penyimpanan time scales, or at high risk of alami and/or anthropogenic disturbance (like in fire-prone regions), should not be used to balance fossil-fuel CO₂ emissions.
For carbon removal that sasarans carbon stores at lower risks of disturbance, it is crucial that net-zero protocols also require an excess amount of CDR as an insurance in the moment of carbon losses.
Similarly, CDR approaches that result in biogeophysical efeks or release gases such as methane and nitrous oxide upon deployment risk fully negating the climate keuntungan of carbon sequestration and should be excluded as a means of balancing fossil-fuel CO₂ emissions.
In cases where biogeophysical efeks or the release of GHGs partly konter the climate keuntungan of carbon sequestration, an additional amount of CDR is also required to compensate these efeks. The measures used to establish equivalency between CO₂ emissions and removals, and biogeophysical and GHG efeks, need to be rigorous and grounded in science.
