In principle, it is possible to achieve a given global temperature target with different combinations of greenhouse gas concentrations in the atmosphere. However, atmospheric CO2 also has a direct effect on some impact sectors, such as ecosystem and crop productivity. Plant growth, and hence productivity, is influenced by the amount of CO2 in the atmosphere. Photosynthesis is dependent on CO2 concentration. An increase in CO2 from current atmospheric levels will stimulate photosynthesis and would feed through to an increase in crop yield, with the precise effect depending on the change in climate. Different combinations of greenhouse gases will therefore, for a given change in climate, produce different impacts and different amounts of avoided impact.
This report describes an assessment of the effect of different combinations of CO2 and non-CO2 greenhouse gases with a given climate change on the regional and global productivity of three agricultural crops – spring wheat, soybean and maize using the GLAM model run with different CO2 concentrations for the same change in climate variables.
The key conclusions are:
- achieving a given climate change target with higher levels of CO2 has relatively little effect on changes in crop productivity at the global scale; • sensitivity of impacts to CO2 concentration vary regionally; • impacts on spring wheat, for a given change in climate, are most sensitive to different CO2 concentrations – meeting the same temperature target with a higher CO2 concentration reduces by a small mount the impact of climate change;
- for maize, changes in CO2 concentration with a given climate change have a negligible effect on yield; there are indications that in some regions the higher the CO2 concentration, the greater the adverse impact of climate change on maize yield.
- •the effect of CO2 enrichment varies between plants (as shown in this analysis), so the results of this project may not be directly transferred to other crop types.