Global Flux-Based Assessment Reveals Declining Ozone Risk for Wheat in Future Climate Change Scenarios.

Tropospheric ozone (O3) is a widespread air pollutant that impairs crop physiology and threatens global food security. Most global-scale assessments have relied on exposure-based metrics, which overlook plant-environment interactions that control O3 uptake. This study presents a global flux-based assessment of future O3 risk for wheat (Triticum aestivum) using a dual-sink dry deposition model driven by Earth System Models from the Coupled Model Intercomparison Project 6 (CMIP6) under three Shared Socioeconomic Pathways (SSP1-2.6, SSP3-7.0, and SSP5-8.5). We quantify phytotoxic O3 dose (POD6) and production losses from 2000 to 2100, analyze regional trends, and perform multiple simulations to assess the influence of soil water availability and atmospheric CO2 on O3 risk. Finally, we explore the roles of radiative forcing (RF), emission policies on O3 precursors (EP), and their interaction, in determining O3 risk changes. We find a general decline in O3 risk, although regional disparities remain. Under SSP1-2.6 (strong EP, low RF) POD6 declines throughout the century, leading global mean production losses to decrease from 3.3% to 5.0% at the beginning of the century to less than 1.4% at its end. In contrast, SSP3-7.0 (weak EP, high RF) shows end-century losses between 1.3% and 4.9% and may exacerbate risks in several regions (South and East Asia, South America, Sub-Saharan Africa). SSP5-8.5 displays intermediate outcomes: O3 risk increases until mid-century in many regions, and then declines by 2100 (0.5%-2.6%), due to delayed EP adoption. Increasing atmospheric CO2 concentrations will likely hinder future O3 risk due to reduced stomatal conductance, but some hotspots will persist near the Southern and Eastern edges of the Tibetan Plateau. These findings provide a basis for prioritizing region-specific mitigation strategies to reduce O3 damage to wheat under future climate conditions.