Crop impacts from compound weather extremes in major breadbaskets under climate change

Staple crops such as wheat, maize, and soybean are essential for global food security, yet they remain highly vulnerable to extreme weather events like heat waves, cold spells, droughts, and excessive rainfall. The interplay between different weather stressors can amplify crop damage significantly. When multiple stressors occur together, their combined impact on yields can be far greater than individual stressors alone. Misunderstanding these complex interactions risks underestimating how climate change could affect agricultural production. In recent decades, global food production has become concentrated in a few key breadbasket regions. Teleconnections such as the El Niño Southern Oscillation (ENSO) can synchronize failures across these regions, posing severe threats to the global food supply and creating food security risks for trade-dependent areas. These adverse weather conditions can lead to compounding impacts across time and space. This thesis aims to improve our understanding of these compound weather risks under climate change by investigating various scenarios affecting crop production. First, I explore the combined impacts of hot and dry summer conditions on U.S. soybean production. Chapter 2 reveals that hot and dry extremes during the flowering stage have the largest impact, reducing yields by factors of four and three compared to hot or dry conditions alone. These extremes arise from strong coupling between soil moisture and temperature in spring and summer, as well as evapotranspiration and temperature interactions during summer. In Chapter 3, I highlight the importance of the sequence of weather stressors. For soybean and maize, warm springs generally benefit yields. However, when followed by hot summers, they can worsen heat damage by up to one-third. Under high-emission scenarios, sequential heat extremes are expected to rise, negating or surpassing the benefits of warmer springs. This nonlinear risk underscores the importance of limiting global warming to 1.5°C to protect food security. Beyond local impacts, simultaneous extreme weather in multiple breadbasket regions can disrupt global food trade and security. In Chapter 4, I examine how large-scale oceanic and atmospheric drivers influence synchronized crop failures in North and South America. Persistent La Niña conditions often result in dry springs over the southeastern U.S. and South America. Additionally, La Niña triggers extra-tropical sea surface temperature patterns that create atmospheric circulation favorable for hot and dry summers. These pathways can lead to concurrent crop losses across these regions. While ENSO’s risk to crop production is known, this study highlights the role of extratropical sea surface temperature patterns in improving predictions of high-impact failures. The 2012 global soybean failure exemplified these dynamics. In Chapter 5, I use a storyline approach to quantify the role of anthropogenic warming in this event. One-third of the 2012 production deficit can be attributed to human-induced climate change. If global temperatures rise by another 1°C, the impacts could increase by 50%. This amplification is driven by thermodynamic factors, as the 2012 atmospheric circulation pattern was applied to current and future climate scenarios. Although the frequency of persistent La Niña events remains uncertain, this study shows that climate change has already intensified their impacts on global soybean production. The storyline approach also demonstrates how to attribute impacts to greenhouse gas emissions by considering atmospheric circulation anomalies. In conclusion, this thesis shows that compound weather extremes pose a growing threat to global crop production. Hot and dry conditions, sequential heat extremes, and large-scale teleconnections like ENSO can cause severe, often synchronized, yield losses. Recognizing these interactions and their drivers is essential for accurately predicting future risks and mitigating climate change impacts on food security. Limiting global warming to 1.5°C is critical to reducing these risks and ensuring resilient agricultural systems.