Rising Temperature and Decreasing Yield

Nowadays, reports about global warming, terrible weather, disasters and food shortage appear now and then. The changing climate brings people unhappiness and great loss. Scientists tell us that the change of climate definitely influences agriculture all over the world. The yield of crops is affected to a large extent. But they are not sure how great the influence would be in the future. Recently, a study in America has brought us some implications on the topic. 
David Lobell, a professor at Stanford University, said that we were trying our best to solve the future problems. It was frustrating that many people thought these future problems would not happen until many years later. Actually, if we do not do something, the future problems would come earlier. Therefore, we have to make these problems clear and solve them as soon as possible. 
David and his colleagues recorded the yields of corn, rice, wheat and soybean from the year of 1980 to the year of 2008. They also put forward a mode of climate change after they had studied the statistics of temperature and rainfalls. They related all the statistics to each other and found some implications. 
The researchers published an online article about the findings on Nature Magazine on May 5th. The article has indicated that compared with the yields when global warming did not happen, the worldwide yield of corn has decreased by 3.8%, while the yield of wheat all over the world has reduced by 5.5%. The article has also reveals that the yield of rice and that of soybean remain almost the same. But in some areas, the changes have been extraordinary. David said that the results were same with former statistics provided by IPCC. Besides, the article has suggested that although the influence of temperature on yields is astonishing, the affects of rainfalls on yields are limited. In all, we can find that in general, the rising temperature influences the yield to some extent. 
John Reilly, an expert at Massachusetts Institute of Technology, pointed out that these results were inspiring but not convincing. Many other factors, such as the prices of crops, the environmental influence and the change of technology should be taken into consideration. These factors would weaken the influence of temperature on yields. He also said that the increasing carbon dioxide in the atmosphere would do goods to the growth of plants. As a result, the yields would probably increase instead of decreasing. However, David argued that, according to his research, the goodness of carbon dioxide is exaggerated. Too much carbon dioxide would do harms to crops.