The risk to food security posed by global environmental change is one of the most significant threats to health and economic stability for a large fraction of the world’s population. Studies suggest a strong response of crops to climate variability and change, due to impacts of changes in e.g. water availability, and temperature (e.g. Challinor et al., 2014). In addition to climate, surface tropospheric ozone pollution is known to impact crop yield, by limitation of plant growth, acceleration of leaf senescence, and direct injury to leaf tissue (McKee et al., 1997). Several studies provide evidence of ozone-induced reduction in crop yield in sensitive major food crop species across Europe and North America (Hollaway et al., 2012), with an estimated annual cost to arable production of ~7 billion Euro and $2-4 billion respectively. Despite this progress in knowledge, few studies have integrated both climatic and ozone impacts, nor the dependence of these combined impacts on future emission mitigation scenarios.
The aim of the PhD is to quantify the combined impact of climate change and ozone on crop yield using the GLAM-ROC model (see below).A number of scenarios will be investigated, including current legislation, and a number of mitigation scenarios. The approach will be to investigate potential realistic emission pathways over the next 30-50 years, focusing on the climate (temperature, precipitation) and tropospheric ozone responses in these scenarios, and determining their coupled impacts on crop productivity. An important component of this work will be the development and evaluation of GLAM-ROC for combined stresses, particularly the co-occurrence of drought and ozone pollution, which is observed in several regions and is expected to occur with increasing frequency in a warmer climate. Driving data for ozone and climate variables are available from Earth system model simulations that submitted experiments covering numerous different future mitigation scenarios as part of the 6th Coupled Model Intercomparison project (CMIP6 – Eyring et al., 2016), including the contribution from the UK Earth System Model (UKESM1).
The study regions (e.g. India, Southern Europe) will be determined as part of the project, based on an initial analysis of ozone damage hotspots, and investigation of regions where potential interactions between drought stress and ozone stress may become increasingly important.
· Quantify the combined impact of climate change and ozone on crops for a range of realistic emission/mitigation and legislation scenarios.
· To separate out the changes in O3, and subsequent impacts on crops, that are solely due to climate and those that are due to precursor emissions.
· Design and conduct future climate mitigation experiments with the latest version of UKESM1 that minimises the future climate and O3 impacts on crops
The GLAM-ROC model (Droutsas et al., 2020) is a world-leading approach, developed at Leeds, to the modelling of crop response to ozone and climate. The model expresses crop responses to environment as a set of simultaneous equations, which are then solved using the Newton–Raphson method. This project will use GLAM-ROC to quantify the effect of varying atmospheric ozone concentrations and climatic parameters (temperature, precipitation) on the yield of selected crops, beginning with wheat.
Existing ozone and climate output from UKESM1 and potentially other Earth system models will be used to drive GLAM-ROC for a range of climate and pollution emissions scenarios. These simulations are available from different mitigation scenarios conducted as part of the CMIP6 project, in addition to more recent simulations driven by new state-of-the-art emissions datasets for short-lived climate pollutants (SLCPs) (including ozone precursors), developed for the AMAP assessment of Arctic SLCPs. These scenarios cover a broad basket of climate and air pollution mitigation policies, including Paris compliance and technological measures for aggressive ozone precursor reductions. Using model scenarios that separate ozone response to climate from precursor emissions only, driving factors for future climate and ozone risk to crop yields will be quantified. An additional aim will be to assess how the combined ozone and climate risk to crops compare with their separate impacts, and to quantify the degree of linearity in combining these factors.
The CASE partner is the UK Met Office, who have a strong interest in both the ongoing development of UKESM and its application to food security. The project will include a critical evaluation of the coupled surface ozone-climate response of UKESM and the impacts on crop yields over a range of climate and emission mitigation scenarios, and how this response compares with a range of other leading ESMs. This constitutes a valuable model evaluation in a highly applied context, including direct application to metrics relevant for air quality and food security. It is expected that the student will also investigate key processes linking surface ozone and drought response (e.g. soil moisture, stomatal conductance) in the ESM model framework using their own UKESM simulations, and how these drive changes in ozone air quality and climate in key world regions for crop production.