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 concentratio n, [CO2](a), also increased during that time period, and although crop growth and yield can respond positively to [CO2](a) increase, yield i ncreases were due mainly to factors other than increasing [CO2](a). Si milarly, some yield increases prior to 1900 were also associated prima rily with factors other than changes in [CO2](a). In particular, past national average yield increases were the result chiefly of technologi cal advances such as nitrogen fertilization; selection of genotypes wi th increased harvest index and disease resistance; mechanization of pl anting, cultivation, and harvesting; and chemical weed and pest contro l. If technology continues to increase average yields at recent rates, near-future increases in [CO2](a) will have only small impacts on yie ld in comparison to technology in many countries. Conversely, if futur e increases in [CO2](a) are the main drivers of future yield increases , those yield increases will be small. These points are demonstrated t hrough 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 i t climatic changes that could have negative or positive impacts on fut ure yield. (C) 1998 Elsevier Science B.V. All rights reserved.