Da qi CO₂ bian hua yu qi hou

In geological history, the earth's climate changed regularly and constantly and the concen- tration of atmospheric CO₂ ~dso changed over time, so scientists argue whether there were response- feedback effects between them. In this paper, global climate change is assumed to be a multiple time- scale change, various time scales including long time orbital-scale, thousand year time-scale and nearly hundred years are introduced and analyzed. For long time-scale, both average global tempera- ture and atmospheric CO₂ level present a reduction trend. Many times during geological history, at- mospheric CO₂ level rose, sometimes to as high as ten times of the present level. It is found that the high C0₂ level period was not always corresponding to the high temperature period. For thousand year time-scale, it is found that ＇warm periods emerged at all global continents, for instance, the tempera- ture in medieval period was even higher than that of today. During the past one hundred year, the average global temperature rose by O. 74 ℃, and there are different understandings about the reason. It is too early to say that the global warming since the industrial revolution was mainly caused by human activities. Further investigation are required.