The National Agriculture and Food Research Organization (NARO) in Tsukuba City, Ibaraki Prefecture, estimated that the domestic rice yield will decrease by about 20% at the end of the 21st century from the end of the 20th century if global warming continues. NARO also points out that the percentage of low-quality rice is expected to rise, emphasizing the need to take such measures as introducing heat-tolerant varieties.
NARO conducted experiments in which the concentration of carbon dioxide (CO2) around rice paddies it owns in the prefectures of Iwate and Ibaraki was artificially increased for 20 years from 1998 to see how this would impact the yield and quality of rice.
It is said that high concentrations of CO2 activate photosynthesis and improve yields. But NARO found that the higher the temperature, the less effective the CO2 was in increasing yields. In a year when the average temperature of the month after the ears of rice came out was 30 degrees, the increase in yield was minimal. (Abridged)