Interaction of Climate Extremes, Air Pollution and Agro-ecosystems

Future food production, and consequently food security, is very sensitive to both climate change and air pollution. So far, little is known about how climate extremes and ozone pollution interact to affect agriculture or about the relative effectiveness of climate change adaptation and ozone regulation measures for various crops and regions. In the CiXPAG project, we investigated the complex interactions between climate extremes, air pollution and agricultural ecosystems in different parts of the world. CiXPAG field experiments in India and Brazil show that enhanced irrigation mitigates the reduction of growth conditioned by abnormal cold or warm temperatures. Studies also confirm that the enhanced carbon dioxide (CO2) concentration can improve the plants' physiological tolerance to the negative effects of ozone, but that varies between different types of plants. Field experiments, particularly in India, revealed significant wheat yield reductions under elevated surface ozone with effects on total biomass, leaf area and grain weight and quality, suggesting that ozone is a serious threat to wheat yield in Indo-Gangetic Plain. In the future, even under moderate global climate warming, India will face more heat extremes, as shown in independent methods applied in CiXPAG using regional models and statistical downscaling. Current management practices to mitigate climate change in terms of irrigation can in turn amplify the ozone impacts due to increased uptake of ozone by the plants when well-irrigated. In CiXPAG, we further developed the DO3SE crop model to allow estimates of the effect of ozone and climate variables in combination, so that we can assess the future influence of these two integrated stresses on crop yield and productivity to allow effective targeting of mitigation and adaptation efforts. The DO3SE model has been evaluated under Indian conditions using experimental data for wheat (collected in the field experiments) and applied to explore the evolution of ozone and climate variable stress over time from 1990 to 2050 using simulated ozone and climate data. The findings suggest that it would be advisable to establish an Air Quality Guideline to target emission reductions to protect agriculture from the ozone pollution. According to CiXPAG results, the effect of ozone pollution removal (i.e. improved air quality) is positive on the total welfare in India. Surveys with farmers and policy makers in the Indo-Gangetic-Plain have further revealed that conventional adaptation (focused only on technological aspects) narrows the problem context and ignores the political economy of local decision makers. Key findings are that technological adaptation strategies do not align with how households adapt and that adaptation in agriculture needs to move beyond impacts on production. This means that the framing of adaptation needs to be broadened, seeing climate change as only one aspect of multiple challenges that people are facing due to environmental and societal change. Some key points brought forward to stakeholders in workshops are the need to increase monitoring of ozone, better understand the links between urban and rural areas (both in terms of pollution transport, but also in socio-economic terms), use "airshed-" rather than local approaches for mitigation, to tailor dose-response curves region-specific crop varieties, and to model impacts of different stresses such as heat, water, irrigation and ozone.

The CiXPAG project was impactful in raising awareness of the threats posed by surface level of ozone and its phytotoxic effects on crop productivity in combination with climate change. The project identify potential trade-offs between current agricultural management practices to enhance productivity under climate change (i.e. increased use of irrigation) but that may increase sensitivity to air pollution. The project also provided useful information on the role that air pollution impacts on agriculture may play in reducing the financial benefit of government policies aimed at supporting farmer's livelihoods. Workshops held during the project with scientists and stakeholders provided a good platform for sharing knowledge and experiences on crop yield impacts due to climate change and ozone, monitoring of pollution, and policy and science challenges. The project contributed overall to a better understanding and collaboration of scientists from different disciplines.

Future food production, and subsequently food security, is very sensitive to both climate change and air pollution. Climate extremes, in particular, can exert substantial stress to agricultural ecosystems and often co-occur with air pollution events. Ground-level ozone is being recognized as the major air pollutant responsible for crop yield losses. Little is known about how climate extremes and ozone pollution interact to affect agriculture, or about the relative effectiveness of climate change adaptation and ozone regulation measures for different crops and regions. In CiXPAG, we will investigate the complex interactions between climate extremes, air pollution and agricultural ecosystems. State-of-the-art global and regional climate model simulations will be combined with statistical downscaling approaches to provide better information on climate extremes relevant to agriculture. We will further develop a flux-based approach in ozone chemistry and climate models. A novel and more consistent approach to include the ozone effect in statistical crop growth models will increase our understanding of the interplay of environmental factors, such as downscaled climate information and air pollution, on agricultural ecosystems. The development of these models will be informed by field experiments describing the effect of climate and ozone on selected crops. The modelling results will be embedded in the particular socio-economic and political context of the study region (Indo-Gangetic-Plain, India) that contributes substantially to regional and global food supply, but is threatened by climate extremes and air pollution. A contextualized understanding of potential responses will be jointly developed by farmers, researchers and policy makers to support effective climate change adaptation and air pollution regulation measures. Knowledge generated in CiXPAG will be relevant also for other significant food producing and exporting countries and regions (e.g., Europe, Brazil).