Global impacts of climate change on yields cannot be estimated due to variation among locations and crop types. But the overall impact on grain is negative—the potential yield loss is about 5 percent for each degree Celsius of global warming.
Lobell et al., 2011
Methods, caveats and issues
Assumptions and Details:
Interactions among changes in rainfall, temperature, extreme climatic events, atmospheric carbon dioxide concentration and pests and diseases are largely unknown and could substantively affect impacts on crops and their yields in ways that are not yet understood.
There is considerable debate about the role of carbon fertilization of crops under conditions of increased atmospheric carbon dioxide. There is no mechanistic basis for a direct effect of CO2 on C4 photosynthesis and the weight of evidence indicates that in plants, such as maize, C4 photosynthesis is not directly stimulated by elevated CO2. However, growth and yield may benefit indirectly through a reduction in stomatal conductance. Free-Air CO2 Enrichment (FACE) experiments indicate that elevated CO2 improves C4 water relations and so indirectly enhances photosynthesis, growth and yield by delaying and reducing drought stress. In addition, a meta-analysis conducted by Taub et al. (2008) suggests that the increasing CO2 concentrations of the 21st century are likely to decrease the protein concentration of many human plant foods (Thornton et al. 2012).
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