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

Many studies have looked at the global response of agricultural systems to changes in cli- mate [1–3, 5, 8, 15], as well as the relative importance of where the agricultural impacts occur [10–13, 16]. In recent years, attention has begun to turn toward the implications of interna- tional trade on the U.S. agricultural sector in particular, finding that international trade effects for the U.S. agricultural sector are comparable in importance to direct, domestic impacts [10–12, 16]. Zhang et al [16] found that considering full, global climate impacts causes significant changes in the projections of U.S. production and exports of crops. Costi- not et al [12] and later Gouel and Laborde [11] examined the aggregate impact of widespread local yield changes on global agricultural markets, again finding that the full picture is neces- sary to understand the future, as comparative advantages among regions shift with particular attention paid to domestic adjustments in land allocation. Finally, Baker et al. [10] extended these findings to a new modeling application, determining that not only does considering global markets cause significant changes in the projections of U.S. agricultural crop produc- tion relative to a U.S. only focused study, but also that freer trade may help buffer local pro- ductivity shocks. These results suggest the potential for meaningful effects on the financial revenue of the U.S, agricultural sector through changes in both domestic production and international prices.

In this paper, we systematically explore the implications of changes to domestic and inter- national temperature and precipitation for U.S. agricultural crop production using a region- ally-resolved, global scale model of energy, land, economic, and climate systems: the Global Change Assessment Model (GCAM). This paper adds to the literature by providing a comple- mentary quantification and replication of the production effects explored in Baker et al. and other modeling efforts with a different model. The analysis in this study is conducted using a modified version of GCAM 5.2 [17] (additional documentation http://jgcri.github.io/gcam- doc/toc.html). GCAM is a global model that couples representations of the energy system, the economy, agriculture and land-use, water, and the global climate in a single computational platform. We explore sensitivity to spatially heterogeneous future impacts by incorporating a subset of the 35 yield change scenarios from the AgMIP global gridded crop model (GGCM) inter- comparison study [8] into GCAM’s exogenous agricultural assumptions. The scenarios selected have been found to span a range of global impacts in previous GCAM versions [18]. Each GGCM assesses the effects on yields of RCP 8.5 changes in CO2 (including fertilization effects), temperature, and precipitation from five bias-corrected global circulation models (GCMs) for rainfed and perfectly irrigated versions of crops. Water for irrigation is con- strained in the version of GCAM used for analysis. We apply crop impacts in one of two ways:

(1) only in the U.S. (to isolate domestic effects) and (2) everywhere (to calculate the combined effects of direct biophysical impacts and international dynamics). This work is consistent with earlier work using different models to consider similar scenar- ios regarding the importance of international impacts, adding robustness to the findings [10–12, 16] through the use of a different multisector model. We find that international impacts could be as important as domestic impacts for the financial value of U.S. agricultural crop production in across spatially and temporally varying agricultural impacts scenarios. Cru- cially, there are scenarios in which examining only domestic impacts would lead to a funda- mentally different analysis of the future of U.S. agricultural crop production than if one considered the combined effects of domestic and international impacts. Therefore, while there is uncertainty about climate impacts on future crop yields, evidence suggests that the impor- tance of international effects on the financial value of U.S. crop production is robust across this uncertainty. 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 2 / 11 research in MultiSector Dynamics, Earth and Environmental System Modeling Program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830. The funders had no role in study design, data collection and analysis,

decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.