Current food trade helps mitigate future climate change impacts in lower-income nations

therefore trade is deemed important for ameliorating the effects of climate change on food security [5]. However, trade also exposes food importing countries to cascading risks from trade embargoes and global price volatility during natural or man-made shocks [6, 7]. Prior studies have offered valuable insights into this topic. Baker et al. (2018) used a global agricultural economic model to explore the impact of global versus domestic climate change on the US agricultural sector, finding increased climate impacts under a global per- spective [8]. Chen and Villoria (2019) identified higher price stability with increased import dependence across 27 net importing countries for maize [9]. Bren d’Amour and Anderson (2020) found that imports contribute to food supply instability in certain Global South countries [10]. Hedlund et al. (2022) examined the impact of climate change on food trade networks, observing high stability for wheat and rice networks but less for maize [11]. Jansenns et al. (2020) investigated various trade liberalization scenarios, highlighting significant benefits in addressing undernourishment through trade adaptation [5]. Other studies have also shock-tested food trade systems by examining the influence of removing crucial producing regions [12–16]. Despite these studies, much of the conversa- tion on climate change and national impact assessments remains domestically focused [17, 18]. We introduce a complementary approach, tailored for national climate impacts assess-

ments, to evaluate cross-border climate risks [17]. Our approach is simple and reproducible, and easily adapted by nations. We intentionally chose not to incorporate prospective trade flows that necessitate projecting global economy forward in time to keep our analysis simple and present a diagnosis based on current trade flows; other studies have used global trade eco- nomics models to explore the impacts of shifting trade patterns [5, 19]. The use of contempo- rary trade portfolios aligns with the recent shift in research focus (away from integrated assessment models) from projecting mid- or end-of-century future conditions to asking, "what would a 1/2/3˚C warmer world do to current agricultural systems and food security?". This framing reduces the levels of uncertainty, allowing us to study the impacts of climate change without the added complexity of long-term economic projections [20]. We investigate how a nation’s total calorie supply is affected by climate impacts on its domestic production alone versus climate impacts over all its supplying regions (see conceptual framework in next sec- tion). These calories include those for human consumption, livestock feed, industrial purposes, and wasted. We do not consider nutrition, consumer acceptability, or household-level food security. Our analysis includes the three major staple crops–wheat, maize, and rice–that together contributed 43% of global calories produced and 87% of global cereal traded in 2010, and largely dominate trade related supply and price concerns under food crises. To align with

policy discussions, we adopt a global mean warming approach, assessing climate impacts for future warming of 1˚C and 2˚C compared to present-day, rather than a time-based approach [21]. Our estimated crop yield impacts are influenced by changes in temperature, precipita- tion, radiation, and also associated carbon dioxide concentration. We focus on results for 2˚C additional global mean warming in the main text (see Supplementary Information for results with 1˚C additional future warming). We use observed global bilateral trade flows of crop commodities corrected for re-exports [22, 23], modelled estimates of climate change impacts on crop yields [24], and spatial crop production data [25]. We also examine how key mega-exporters, those countries that three or more countries rely on for at least 10% of their calorie supply, influence climate impacts. Mega-exporters have a disproportionately large impact on global food supply, as demonstrated by the food price spikes related to the ongoing Ukraine-Russia conflict [26]. PLOS ONE Current food trade helps mitigate future climate change impacts in lower-income nations PLOS ONE | https://doi.org/10.1371/journal.pone.0314722 January 3, 2025 2 / 16 convert quantities to calories can be accessed from the Harvard Dataverse (https://doi.org/10.7910/ DVN/GNFVTT). Funding: KB was supported by the University of British Columbia’s Four Year Doctoral fellowship. NR was supported by NSERC Discovery Grant RGPIN-2017-04648 and the Canada Research Chairs Program. TH acknowledges support from the National Science Foundation (CBET-1855937,

SES-1463644, OISE-2020635 and DEB-1924111) and the U.S. Department of Agriculture, National Institute of Food and Agriculture (IND01053G2). TK and FS acknowledge funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) project No. KA 4815/1-1, and the German Federal Ministry for Economic Cooperation and Development (grant no. GS22 E1070-0060/ 029). JJ was supported by the NASA GISS Climate Impacts Group, the Open Philanthropy Project, the Future of Life Institute, and the USDA grant 59- 6000-0-0071. 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.