Science Briefs

Fundamental Improvement in Robustness of Climate Change Impact Assessments for Agriculture

Climate change impact assessments help identify and quantify risks to the world's food supply, as well as evaluate sustainable adaptation and mitigation strategies.

Photo of a wheat field.

Figure 1. A wheat field in Clermont-Ferrand, France. (Credit: Alexander Ruane/AgMIP)

An international team of agro-climatic experts, organized by the Agricultural Model Intercomparison and Improvement Project (AgMIP) and the Joint Research Commission (JRC) of the European Union, collected and evaluated experimental and modelling research with the goal of improving climate change impacts assessments on food. This work concludes a two-year activity of the team that started during a workshop on the effects of carbon dioxide (CO2) on crops co-organized by AgMIP and the JRC in Ispra, Italy, in 2018. We reported on our findings in an article (Toreti et al., 2020) recently published in the journal Nature Food.

Crop responses to rising atmospheric CO2 concentrations, together with projected variations in temperature and precipitation, will determine future agricultural production (Fig. 1). Carbon dioxide enrichment experiments using greenhouses, growth chambers, gradient tunnels, open-top chambers (OTC), and Free-Air CO2 Enrichment (FACE) techniques are conducted to study the role of increased CO2 in altering crop physiology (Fig. 2). Evidence from these studies shows that yield of C3 crop species (for example, wheat, rice and barley), under a full complement of water and nutrients, significantly increase with higher CO2 concentrations. Beyond stimulating photosynthesis and growth, elevated CO2 also improves water-use efficiency by reducing crop transpiration. However, a CO2-rich atmosphere also results in reduced nutritional quality, for example lower concentrations of protein, zinc, and iron.

Thermal image of an experimental maize field

Figure 2. Thermal image of the experimental maize field of the Thünen Institute (Braunschweig, Germany) at noon on July 16, 2007, with one FACE ring (24 m diameter) in the foreground. Atmospheric CO2 concentration was increased within the FACE ring (550 ppm) as compared to the remaining field area (378 ppm). The elevated CO2 concentration effected an increase of the canopy surface temperature of about 2°C as shown here, which resulted from a decrease of stomatal conductance and whole plant transpiration by about 20%. (Credit: Remigius Manderscheid, Thünen-Institut)

Crop growth models are key tools for scaling-up experimental evidence and assessing regional and global outcomes. Process-based crop models simulate the interactions of biophysical, climatic and environmental processes, including elevated CO2 on plant growth, crop yield, and nutrient quality. The large and growing body of experimental evidence has shown that current crop modelling approaches are increasingly able to capture the main effects of increased CO2 on crop growth and yield under a wide range of growing conditions at field scale (Fig. 3).

Previously, crop modelling has usually been carried out for scenarios that both include and exclude the effects of increased atmospheric CO2 concentration on crops, as the uncertainties were considered too high to exclude one of the two. The team concluded that recent efforts and the accumulated evidence are such that scenarios that exclude the effects of CO2 can finally be eliminated from climate change impact assessments.

Scatter plot with line fit of wheat grain responses to eCO2

Figure 3. Wheat grain yield responses to eCO2 from a mixing ratio of 365 ppm to 550 ppm measured in the 2007–2009 Horsham FACE experiment (south-eastern Australia) under different water supply conditions (dry and supplemental irrigation). (Credit: Toreti et al., 2020)

Now, the uncertainties can be narrowed in the climate change impact assessments for agriculture that are used to inform policymakers and to design future adaptation and mitigation strategies. AgMIP — whose coordinating office is managed at the NASA Goddard Institute for Space Studies and Columbia University's Center for Climate Systems Reearch — is a community of experts advancing methods for improving predictions on the future performance of agricultural and food systems under a changing climate. AgMIP plays an important role in delivering rigorous scientific results that assess the potential biophysical and socio-economic consequences and support national and international climate and agricultural policies.

Therefore, the paper proposes a roadmap for the coming years to support targeted experimental and modelling research. Key elements of the roadmap include measurement of crop nutrients in experiments and use of multi-model ensembles to project the complex effects of climate extremes on food security.

Reference

Toreti, A., D. Deryng, F.N. Tubiello, C. Müller, B.A. Kimball, G. Moser, K. Boote, S. Asseng, T.A.M. Pugh, E. Vanuytrecht, H. Pleijel, H. Webber, J.L. Durand, F. Dentener, A. Ceglar, X. Wang, F. Badeck, R. Lecerf, G.W. Wall, M. van den Berg, P. Hoegy, R. Lopez-Lozano, M. Zampieri, S. Galmarini, G.J. O'Leary, R. Manderscheid, E. Mencos Contreras, and C. Rosenzweig, 2020: Effects of elevated CO2 on agriculture: Narrowing the uncertainties. Nat. Food, 1, no. 12, 775-782, doi:10.1038/s43016-020-00195-4.

Please address all inquiries about this research to Dr. Cynthia Rosenzweig.

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