The domestic and international implications of future climate for U.S. agriculture in GCAM

GCAM, this land type is often the first and most impacted by cropland area changes. An exception is the HadGEM2-EPIC scenario: cropland areas decrease to such an extent that both other arable land and forest expand. The changes in total cropland area in the EPIC scenarios reported in Table 1 are generally smaller in magnitude than those reported in [10]. While GCAM’s simulations run through 2100, results are presented in 2050 for ready com- parison with other results in the literature. S4 and S5 Figs present the 2100 data for the same variables as Figs 2 and 3 and S3 Fig; the relationships between the Domestic and Full scenarios that occur for each climate-crop combination observed above for 2050 data persist in 2100. The persistence of the relationships between Domestic and Full scenarios across time and across spatially heterogenous, varied climate-crop combinations again highlights the impor- tance of accounting for international dynamics in examining agricultural quantities. 4 Conclusions Even given the uncertainty in future agricultural changes, the importance of international effects on U.S. agricultural crop production and prices is robust across the widely varying sce- narios studied here. Specifically, in many of the scenarios considered, the inclusion of impacts globally reverses the projected direction of change from reference compared to applying impacts only domestically for several key agricultural commodities. These findings are again consistent with other models in the literature, and adds an additional regionally resolved,

global-scale multi-sector economic model’s results to confirm the importance of examining global systems, particularly agricultural systems, holistically, as conclusions may fundamen- tally change when only domestic impacts are considered. At the same time, more research on the issues explored in this paper is needed to develop a deeper understanding of how future climate may affect the agricultural system across the globe. There are opportunities for future work across both the human and the Earth system sides of agriculture. For example, the type of analysis in this paper could be applied to any country or region of interest that is coupled to international agricultural commodity markets. In addition, our examination has focused on the producers of agricultural products. We have not attempted to analyze the effects of external and domestic changes in climate on consumers, whose interests are different and deserving of separate analysis. Next, a wide variety of differ- ent trade patterns and regimes could emerge over the long time period of this study, which could lead to different results. For example, in the absence of flexible trade, or in a more restrictive trade scenario, the balance of domestic effects would become increasingly impor- tant. Another area of future research is to quantify the effect of different socioeconomic Table 1. 2050 percent changes from the no impacts reference GCAM scenario in the U.S. for different land cover types under different impacts scenarios. Total Cropland Other Arable Land Forest Grass, Shrub, Pasture

Model GCM Domestic Full Domestic Full Domestic Full Domestic Full EPIC GFDL -0.95 -2.92 1.11 4.42 0.42 0.73 0.01 0.25 EPIC HadGEM2-ES -5.57 -4.57 5.00 1.57 2.31 2.62 0.22 -0.04 EPIC IPSL -0.89 -0.31 -1.44 -3.64 0.73 0.95 -0.01 -0.17 EPIC MIROC -4.31 -3.76 4.37 3.20 1.66 1.65 0.20 0.11 EPIC NORESM1 -1.84 -1.81 4.05 4.11 0.34 0.30 0.14 0.14 LPJmL GFDL 1.12 -3.10 -1.93 6.53 -0.15 0.16 -0.15 0.47 LPJmL HadGEM2-ES 0.97 -1.16 -2.54 1.82 0.04 0.19 -0.16 0.15 LPJmL IPSL 1.43 0.75 -2.53 -0.50 -0.20 -0.32 -0.18 -0.03 LPJmL MIROC 1.06 -0.67 -2.90 1.14 0.00 -0.01 -0.15 0.14 LPJmL NORESM1 1.49 -2.04 -2.37 5.04 -0.29 -0.11 -0.17 0.37 https://doi.org/10.1371/journal.pone.0237918.t001 PLOS ONE The domestic and international implications of future climate for U.S. agriculture in GCAM PLOS ONE | https://doi.org/10.1371/journal.pone.0237918 August 28, 2020 8 / 11