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

The COVID-19 pandemic and recent extreme weather events [1] have highlighted the potential for disruptions to global supply chains when countries close borders or prioritize domestic demand [2–6]. In 2021, a massive container ship blocked the Suez Canal for nearly a week, causing waves of disruptions and delays on global supply chains, ranging from shortages of oil and natural gas supply in Europe to coffee and toilet paper shortages in the US [7, 8]. This effect of blockage at Suez Canal is transmitted to regions globally via trade, with continu- ing interactions with different sectors. While trade can benefit both importers and exporters, importing countries are vulnerable to disruptions in world markets [9]. Supply disruptions and domestic market reconfigurations can alter trade patterns, as was seen with the pandemic [10, 11] and the 2007–08 international food crisis [12, 13]. Climate change impacts on crop yields are heterogeneous across countries and regions, with the effect of changes in one country transmitted to others via trade. Although studies have generally shown net negative impacts on yields at a global level, some regions will experi- ence improved yields while others have losses, changing the comparative advantage of current agricultural producers and trade dynamics [14–19]. International trade could play a role in mitigating the negative regional consequences of cli- mate change impacts on crop yields. Previous studies have analyzed agricultural welfare loss under climate change and trade regimes at a global scale [20, 21]. They found integrated world

markets largely buffer the adverse food security impacts due to climate change. However, Cost- inot, Donaldson [15] concluded that international trade plays a minor role in reducing climate impacts on global GDP, though this conclusion has been criticized due to the high elasticities of food supply and demand assumed in the model [22]. To better understand the interactions of non-linear and globally coupled agricultural-bioe- nergy-water systems under the broader economy, and in response to agricultural trade and cli- mate change impacts, we introduce systematic perturbations to a global integrated human- Earth system model in two dimensions. First we explore the role of international trade patterns via cereal import dependency constraints, as a change in the human system dimension. Sec- ond, we examine changes to the Earth system via climate change impacts on crop yields. Per- turbations are introduced both separately and in combination, allowing us to distinguish the consequences of individual perturbations and interactive effects. We use the Global Change Analysis Model [GCAM v5.3; 23], a global, fully integrated model of the socioeconomic, energy, land, and water systems, to disentangle the individual roles of national and regional engagement in global markets and climate change and the non- linear interactions between these two systems over the period of 2015–2050. We track a set of multi-sector outcomes—crop production and consumption, exports, imports, crop prices, caloric consumption, agricultural revenue, net trade revenue, the food expenditure share of

income, irrigation water consumption, and crop-based ethanol production. We find that decreased participation in global markets due to all regions implementing a zero cereal import dependency strategy leads to decreases in total cereal production and con- sumption at the global scale. Although some regions show increases in production or con- sumption, no region shows increases in both. The impact of reduced international trade on production and consumption of cereals is stronger than climate change in most regions. The influence of climate change on crop yields also has strong impacts across regions, with rising domestic prices and declining consumption of cereal crops in general. Enforcement of a zero import-dependency for cereal crops exacerbates the effects of climate change in regions with higher baseline import dependence. Other outcomes, such as trade and crop producers’ reve- nue, irrigation water consumption, and crop-based ethanol production, are more sensitive to the resulting changes in international trade due to zero import-dependence than to climate change, with the largest effects displayed in regions with large share of base-year cereal 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 2 / 18 Competing interests: The authors have declared that no competing interests exist.