Maladaptation in cereal crop landraces following a soot-producing climate catastrophe.

Aerosol-producing catastrophes like nuclear war or asteroid strikes, though rare, pose serious risks to human survival. The injected aerosols would reduce solar radiation, lower temperatures, and alter precipitation, impacting crop productivity, including for locally adapted traditional crop varieties, i.e. landraces. We assess post-catastrophic climate effects on crops with extensive landrace cultivation, barley, maize, rice, and sorghum, under climate scenarios that differ in the quantity of soot injection. Using a crop growth model, we estimate environmental stress gradients and together with genomic markers apply gradient forest offset methods to predict post-catastrophic maladaptation in landraces over time. We find landraces are most maladapted where soot-induced climate shifts were strongest. Validating our approach, gradient forest models successfully capture a signal of maize landrace adaptation in common gardens across Mexico. We further use our gradient forest models to identify landrace varieties best matched to specific post-catastrophic conditions, indicating potential substitutions for agricultural resilience. The best substituted varieties require long migration distances, often across country borders, though countries with more climatic diversity have better within-country substitutions. Our findings highlight that a soot-producing catastrophe would drive global maladaptation in landraces and suggest current adaptive diversity is insufficient for agricultural resilience.