Perspective on the relative insignificance of increasing atmospheric CO2 concentration to crop yield

Average yield of most crops in many countries increased significantly during the past 50 to 100 years. Although atmospheric CO2 concentration, [CO2](a), also increased during that time period, and although crop growth and yield can respond positively to [CO2](a) increase, yield increases were due mainly to factors other than increasing [CO2](a). Similarly, some yield increases prior to 1900 were also associated primarily with factors other than changes in [CO2](a). In particular, past national average yield increases were the result chiefly of technological advances such as nitrogen fertilization; selection of genotypes with increased harvest index and disease resistance; mechanization of planting, cultivation, and harvesting; and chemical weed and pest control. If technology continues to increase average yields at recent rates, near-future increases in [CO2](a) will have only small impacts on yield in comparison to technology in many countries. Conversely, if future increases in [CO2](a) are the main drivers of future yield increases, those yield increases will be small. These points are demonstrated through a comparison of (i) long-term records of yield, (ii) data from key controlled-[CO2] experiments, and (iii) records of past [CO2](a). Finally, it is noted that continued [CO2](a) increase may bring with it climatic changes that could have negative or positive impacts on future yield. (C) 1998 Elsevier Science B.V. All rights reserved.