After comprehensively analyzing dozens of studies, scientists at the University of Illinois believe that after the average daily temperature rises to a certain level, it will lead to a decline in rice production. Although some American scientists do not fully agree with the basis of this judgment, they also believe that attention should be paid to the impact of climate warming on rice yield.
Elizabeth Ainsworth, a University of Illinois scientist engaged in the study, reported in a new issue of the British “New Scientist†weekly that it is difficult to predict the impact of climate warming on crop yields. Temperature, carbon dioxide concentration, and ozone level have a great influence on crop yields. In addition, the conditions for conducting related experiments in the greenhouse and the natural environment are also different. Therefore, Ainsworth comprehensively analyzed the results of about 80 studies and calculated them. The results show that rice yield will begin to decline in areas where the average daily temperature is expected to exceed 30 degrees Celsius, and the higher the temperature, the greater the reduction in production.
Previously, some scientists believed that although rising temperatures may affect crop yields, the increase in carbon dioxide levels associated with climate warming will lead to increased photosynthesis in crops, and such positive and negative results will offset each other. However, Ainsworth's comprehensive analysis showed that the above positive effects of photosynthesis enhancement are not sufficient to completely offset the negative impact of high temperatures on crop yields.
The new study also found that an increase in surface ozone levels also reduced rice yields. Nitrogen dioxide emitted from power plants can catalyze the production of ozone under warm and sunny conditions. According to the calculation of Ainsworth, if the concentration of ozone in the surface gas of some areas reaches about 60 ppb (ppb is one part in one billion), the local rice production may be reduced by 14%.
But there are also scientists who do not fully agree with Ainsworth's speculation that the ozone level will affect the harvest. They pointed out that many experiments refer to fixed ozone levels, but outdoor ozone levels fluctuate every day. Crops can use the low ozone level to recuperate and rehabilitate their adverse effects when ozone concentration is high. In addition, some studies on the effects of carbon dioxide and ozone on rice yield were carried out separately, and did not reflect the combined effects of these two factors. Related research needs to be carried out in depth.
However, some scientists who participated in the review of the above studies also believe that in order to deal with global warming, new varieties of rice that are resistant to high temperatures and high ozone levels can be considered. Ainsworth pointed out that in the future, tropical regions may need to adapt to new varieties of rice that are warming, because the temperature there is already approaching the limit that traditional rice varieties can tolerate.