Amplified agricultural impacts from more frequent and intense sequential heat events

As the climate warms, interacting weather extremes such as sequential heat events pose complex risks to societies. Regarding global agriculture, laboratory experiments suggest that early crop exposure to heat may either confer tolerance or enhance vulnerability to subsequent heat during the critical crop flowering stage. We show that warm early-seasons improve crop yield potential, particularly for soybean and maize, but also increase the impacts of subsequent heat by 5%-55% compared to years with average early-season temperatures. The impacts of this increased yield sensitivity outweigh the benefits of early season heat when mid-season temperature anomalies exceed 0.7 ∘ C-5 ∘ C (depending on the crop). Analyzing projected temperatures under the Shared Socioeconomic Pathway 3-7.0, we find a tenfold increase in the likelihood of experiencing sequential heat in early and mid-season crop growth stages, defined as a joint 90th percentile event. Accounting for the interactive effects of early and mid-season warming increases projected temperature-related crop yield losses by 2%-44%, depending on crop and region. These results underline the emerging nonlinear risks from sequential heat extremes to food systems, which can largely be avoided when limiting warming to 1.5 ∘ C globally.