Agriculture, bioenergy, and water implications of constrained cereal trade and climate change impacts

consumption decreases for cereal crops and increases for non-cereal crops in both the USA and Brazil, although the magnitude of change is much smaller in the Middle East than USA. Additionally, in the Middle East, the changes in irrigation water consumption in CC is much smaller than in ID, as international trade is able to mitigate some of the negative impacts on crop yields from climate change. Therefore, in IC, the change of irrigation water consumption is similar to ID given its dominant effects in the Middle East. In contrast, in the USA, the increase in irrigation water for non-cereal crops in CC is much larger in mag- nitude than the decrease in ID, resulting in an increase in irrigation water for non-cereal crops in IC. Results for irrigation water consumption across all regions are shown in S6 Fig in S1 File. Ethanol production. While CC has a similar percent change impact on corn ethanol produc- tion in the Middle East and USA, -14% and -18%, respectively, ID results in very different impacts, with a 96% decrease in Middle East and an 11% increase in USA. Note, though, that the corn ethanol production in the Middle East in 2050 is very small in RF, with <15% of the corn ethanol production of the USA. However, the magnitude of change in corn ethanol pro- duction in the Middle East in ID relative to RF is greater than the change in USA (Tables 1 and 2). The near complete elimination of corn ethanol in the Middle East in ID is due to the regional scarcity of cereal crops and a more elastic demand for ethanol than food. In contrast,

in the USA, a major corn exporter, corn ethanol becomes relatively more competitive com- pared to other liquid fuels domestically due to the decrease in global demand for corn in ID. In general, in regions where corn ethanol is available, cereal net importers in RF reduce corn eth- anol production in ID while the cereal net exporters increase corn ethanol production (S7 Fig in S1 File). 4 Discussion Global human and physical Earth systems interact with each other through multiple intercon- nected systems. Perturbations to any of these systems carry implications for both human and physical Earth systems everywhere. Understanding these systems and their interconnectivity can be difficult because only the total effects of multiple, simultaneous perturbations and responses are observed. For instance, the global food supply chain was disrupted by the 2007– 08 international food crisis due to extreme weather impacts on crop yields and the COVID-19 pandemic. A recent study showed that the COVID-19 outbreak led to drastic reduction in trade interconnectedness among countries [32]. The long-term effects of such disruptions on agricultural trade are uncertain. To better understand how human and physical Earth systems interact around a changing climate and constraints on global trade, we evaluate the individual and combined impacts of these changes on multiple sectoral outcomes through 2050. While we analyze only one realiza- tion of climate change impacts on crop yields and one alternative trade perturbation scenario

using global cereal import dependency constraints, the insights to the relative impacts across regions are likely similar to alternate impacts, though the magnitude may differ depending on estimates of yield impacts and degrees of import dependency constraints. The yield changes used in this study have also been applied in other studies [17, 33, 34], with some crops and regions experiencing increases in yields under climate change, but overall climate impacts on agricultural yields are negative. Changes to the land, bioenergy, and water systems would vary in the real world, depending on the degree to which countries might impose constraints on import dependency to combat uncertainty from supply chain disruptions and the regional cli- mate change impacts on crop yields. However, the objective of this study is not to predict future climate impacts or trade patterns, but rather to explore how outcomes across multiple PLOS ONE Agriculture, bioenergy, and water implications of constrained cereal trade and climate change impacts PLOS ONE | https://doi.org/10.1371/journal.pone.0291577 September 15, 2023 14 / 18