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

prices of agricultural commodities; rice, for example, is an essential staple food providing over 20% of the calories consumed worldwide [80]. Overly relying on CDR to offset agricultural emissions would thus hit poor households who spend large shares of their incomes on food the hardest [81]. Unless accompanied by other policies to protect the poor, it could lead to an increase in poverty due to agricultural commodities price shocks [82], exacerbating the inher- ent inequalities in the distribution of impacts due to climate change [83–85]. The approach could moreover entail trade-offs in land-use between low-mitigation agricultural emission sce- narios and increased CDR requirements, although land requirements vastly vary among CDR technologies [7, 21, 36, 86]. This paper explored one single possibility, focused on the agricultural sector, to ensure that deviations from the SSP1-2.6 agricultural emissions pathway do not result in additional cli- mate change and to deliver finances to additional CDR rates. We showed the importance of physically sound approaches to correctly offset non-CO2 agricultural emissions, revealing the shortcomings of currently used conversion metrics. While the required CDR rates to account for deviations from stringent mitigation pathways directly follow from physical laws, distribu- tion of their economic burden is up to negotiation. The burden does not necessarily need to fall on the agricultural sector, given the potential implication for poverty and food security. A

fair distribution should rather also account for historical responsibility as well as current socio-political and economic capacity. To reduce this burden, as well as the risk of relying on unfeasible or unsustainable rates of CDR, strengthening efforts to mitigate agricultural emis- sions within the limits to food security should remain a climate policy priority. Supporting information S1 Text. Supporting discussion. (DOCX) S1 Fig. Additional CDR rates needed to offset agricultural methane and nitrous oxide under the GWP100-based approach (left) and the ERF-based approach (right). (TIF) S2 Fig. Radiative forcing and temperature anomaly under ERF-based offsetting compared to reference scenarios. Effective radiative forcing (ERF) and temperature anomaly relative to the 1850–1900 average under the SSP1-2.6 scenario, under the alternative emission scenario (constant or worst-case), and under the offsetting scheme using the ERF-based approach met- ric. Thick lines represent simulations with best-estimate parameters [65] whereas shaded areas encompass the 95%-interval of the ensemble simulations. a) ERF under the constant agricul- tural emissions scenario. b) Change in temperature under the constant agricultural emissions scenario. c) ERF under the worst-case agricultural emissions scenario. d) Change in tempera- ture under the worst-case agricultural emissions scenario. (TIF) S3 Fig. Radiative forcing and temperature anomaly under GWP100 offsetting compared to reference scenarios, additional nitrous oxide emissions only. Effective radiative forcing

(ERF) and temperature anomaly relative to the 1850–1900 average under the SSP1-2.6 sce- nario, under the alternative nitrous oxide emission scenario (constant or worst-case), and under the offsetting scheme using the GWP100-based approach metric. Thick lines represent simulations with best-estimate parameters [65] whereas shaded areas encompass the 95%- interval of the ensemble simulations. a) ERF under the constant agricultural nitrous oxide emissions scenario. b) Change in temperature under the constant agricultural nitrous oxide emissions scenario. c) ERF under the worst-case agricultural nitrous oxide emissions scenario. PLOS ONE Offsetting future agricultural emissions with CO2 removal PLOS ONE | https://doi.org/10.1371/journal.pone.0247887 March 17, 2021 13 / 19