The impact of weather and increased atmospheric CO2 from 1892 to 2016 on simulated yields of UK wheat

Climate change effects on UK winter wheat grain yield are complex: warmer temperature, negative; greater carbon dioxide (CO2) concentration, positive. In the absence of long-term experiments where temperature and CO2 concentration could be manipulated separately, we used the crop simulation model Sirius with long-term daily meteorological data (1892-2016) for Rothamsted, Hertfordshire, UK (2007-2016 mean growing season temperature 1.03°C warmer than 1892-1991), and CO2 concentration over this period to investigate their separate effects on simulated grain yield each year in three wheat cultivars of the modern era. We show no detectable linear trend in simulated yield over the period 1892-2016 from the effect of weather (comprising daily temperature, rainfall, and sunshine) at 294.50 ppm CO2 (1892 reference value), but a 9.4% increase when combined with increases in atmospheric CO2 (from 294.50 to 404.21 ppm). Estimates of the proportional benefit to yield from increases in CO2 differed amongst cultivars. Notwithstanding considerable inter-annual variation in yield, the positive trend from the simulation studies with actual CO2 values does not match the recent stagnation in UK wheat yield, but cultivar improvement to maximize adaptation to greater CO2 may be feasible