Impacts of Surface Ozone Pollution on Global Crop Yields: Comparing Different Ozone Exposure Metrics and Incorporating Co-effects of CO2

Abstract

Surface ozone (O3) pollution poses significant threats to crop production and food security worldwide, but an assessment of present-day and future crop yield losses due to exposure to O3 still abides with great uncertainties, mostly due: (1) to the large spatiotemporal variability and uncertain future projections of O3 concentration itself; (2) different methodological approaches to quantify O3 exposure and impacts; (3) difficulty in accounting for co-varying factors such as CO2 concentration and climatic conditions. In this paper, we explore these issues using a common framework: a consistent set of simulated present-day O3 fields from one chemical transport model, coupled with a terrestrial ecosystem-crop model to derive various O3 exposure metrics and impacts on relative crop yields worldwide, and examine the potential effects of elevated CO2 on O3-induced crop yield losses. Throughout, we review and explain the differences in formulation and parameterization in the various approaches, including the concentration-based metrics, flux-based metrics, and mechanistic biophysical crop modeling. We find that while the spatial pattern of yield losses for a given crop is generally consistent across metrics, the magnitudes can differ substantially. Pooling the concentration-based and flux-based metrics together, we estimate the present-day globally aggregated yield losses to be: 3.6 ± 1.1% for maize, 2.6 ± 0.8% for rice, 6.7 ± 4.1% for soybean, and 7.2 ± 7.3% for wheat; these estimates are generally consistent with previous studies but on the lower end of the uncertainty range covered. We attribute the large combined uncertainty mostly to the differences among methodological approaches, and secondarily to differences in O3 and meteorological inputs. Based on a biophysical crop model that mechanistically simulates photosynthetic and yield responses of crops to stomatal O3 uptake, we further estimate that increasing CO2 concentration from 390 to 600 ppm reduces the globally aggregated O3-induced yield loss by 21–52% for maize and by 27–38% for soybean, reflecting a CO2-induced reduction in stomatal conductance that in turn alleviates stomatal O3 uptake and thus crop damage. Rising CO2 may therefore render the currently used exposure-yield relationships less applicable in a future atmosphere, and we suggest approaches to address such issues.

Influence of plant ecophysiology on ozone dry deposition: Comparing between multiplicative and photosynthesis-based dry deposition schemes and their responses to rising CO<sub>2</sub> level

“…For the numerical modeling framework, we made use of the Terrestrial Ecosystem Model in R (TEMIR), an offline ecosystem model driven by prescribed meteorology for investigating ecophysiological responses of the biosphere to atmospheric and environmental changes (https://github.com/amospktai/TEMIR). This biosphere model has also been used in previous studies to evaluate global dry deposition fluxes (Wong et al, 2019) and the damage of ozone on global crop production (Tai et al, 2021). In this study, we implemented in TEMIR various representations of dry deposition velocity and stomatal resistance in particular.…”

Approaches to investigate crop responses to ozone pollution: from O3‐FACE to satellite‐enabled modeling

“…Ozone directly damages plants by entering leaves through the stomata and reacting in the aqueous apoplast to produce other reactive oxygen species (ROS) that subsequently accelerate senescence and at high enough concentrations lead to programmed cell death (Ainsworth, 2017 ; Hasan et al., 2021 ). Regions of high O 3 pollution (Figure 1(a) ) correspond with global croplands (Figure 1(b) ) resulting in significant negative effects on crop productivity (Fischer, 2019 ; Mills et al., 2018 ; Tai et al., 2021 ). Fischer ( 2019 ) estimated that O 3 pollution currently reduces wheat ( Triticum aestivum ) yields by more than 20% in India.…”

“…The estimated magnitude of global O 3 impacts on crop yields varies with assumptions about O 3 flux through stomata into leaves and the degree of detoxification within leaves. Still, conservative estimates suggest that current O 3 pollution reduces yield in major staple crops by 3.6% in maize, 2.6% in rice ( Oryza sativa ), 6.7% in soybean, and 7.2% in wheat (Tai et al., 2021 ).…”

GCAP 2.0: a global 3-D chemical-transport model framework for past, present, and future climate scenarios

“…How atmospheric composition and chemistry has changed in the past and will change in the future is of tremendous societal importance. Surface air pollution is the leading cause of preventable death worldwide (GBD 2019Risk Factor Collaborators, 2020 and threatens global food security and ecosystem health (e.g., Tai et al, 2021). Short-lived climate forcers like methane, tropospheric ozone, and aerosol particles influence global and regional climate (e.g., Fiore et al, 2015).…”