Understanding the effects of climate change is vital for food security. Among the most important environmental impacts of climate change is the direct effect of increased atmospheric carbon dioxide concentration ([CO 2 ]) on crop yields, known as the CO 2 fertilization effect. Although several statistical studies have estimated past impacts of temperature and precipitation on crop yield at regional scales, the impact of past CO 2 fertilization is not well known. We evaluated how soybean yields have been enhanced by historical atmospheric [CO 2 ] increases in three major soybean-producing countries. The estimated average yields during 2002-2006 in the USA, Brazil, and China were 4.34%, 7.57%, and 5.10% larger, respectively, than the average yields estimated using the atmospheric [CO 2 ] of 1980. Our results demonstrate the importance of considering atmospheric [CO 2 ] increases in evaluations of the past effects of climate change on crop yields.
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