Offsetting unabated agricultural emissions with CO2 removal to achieve ambitious climate targets

RESEARCH ARTICLE Offsetting unabated agricultural emissions with CO2 removal to achieve ambitious climate targets Nicoletta BrazzolaID*, Jan WohlandID, Anthony Patt Department of Environmental Systems Science, Institute for Environmental Decisions, ETH Zurich (Swiss Federal Institute of Technology), Zurich, Switzerland * nicoletta.brazzola@usys.ethz.ch Abstract The Representative Concentration Pathway 2.6 (RCP2.6), which is broadly compatible with the Paris Agreement’s temperature goal by 1.5–2˚C, contains substantial reductions in agri- cultural non-CO2 emissions besides the deployment of Carbon Dioxide Removal (CDR). Failing to mitigate agricultural methane and nitrous oxide emissions could contribute to an overshoot of the RCP2.6 warming by about 0.4˚C. We explore using additional CDR to offset alternative agricultural non-CO2 emission pathways in which emissions either remain constant or rise. We assess the effects on the climate of calculating CDR rates to offset agri- cultural emission under two different approaches: relying on the 100-year global warming potential conversion metric (GWP100) and maintaining effective radiative forcing levels at exactly those of RCP2.6. Using a reduced-complexity climate model, we find that the con- version metric leads to a systematic underestimation of needed CDR, reaching only around 50% of the temperature mitigation needed to remain on the RCP2.6 track. This is mostly because the metric underestimates, in the near term, forcing from short-lived climate pollut-

ants such as methane. We test whether alternative conversion metrics, the GWP20 and GWP*, are more suitable for offsetting purposes, and found that they both lead to an over- estimation of the CDR requirements. Under alternative agricultural emissions pathways, holding to RCP2.6 total radiative forcing requires up to twice the amount of CDR that is already included in the RCP2.6. We examine the costs of this additional CDR, and the effects of internalizing these in several agricultural commodities. Assuming an average CDR cost by $150/tCO2, we find increases in prices of up to 41% for beef, 14% for rice, and 40% for milk in the United States relative to current retail prices. These figures are signifi- cantly higher (for beef and rice) under a global scenario, potentially threatening food security and welfare. Although the policy delivers a mechanism to finance the early deployment of CDR, using CDR to offset remaining high emissions may well hit other non-financial con- straints and can thus only support, and not substitute, emission reductions. PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0247887 March 17, 2021 1 / 19 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Brazzola N, Wohland J, Patt A (2021) Offsetting unabated agricultural emissions with CO2 removal to achieve ambitious climate targets. PLoS ONE 16(3): e0247887. https://doi.org/ 10.1371/journal.pone.0247887 Editor: Yangyang Xu, Texas A&M University, UNITED STATES Received: September 22, 2020 Accepted: February 15, 2021 Published: March 17, 2021

Copyright: © 2021 Brazzola et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All data used to produce the analysis is already publicly available at the SSP and RCP database managed by IIASA (https://tntcat.iiasa.ac.at/SspDb/dsd?Action= htmlpage&page=10 and https://tntcat.iiasa.ac.at/ RcpDb/dsd?Action=htmlpage&page=welcome). The code to replicate the analysis is available at GitHub (https://github.com/jwohland/offsetting_ agricultural_emissions). Funding: J.W. is funded through an ETH Postdoctoral Fellowship and acknowledges support from the ETH Foundation and the