Bian xi 'qi hou bian nuan'

In recent years，controversy about global warming and its mechanism have reached an unprecedented level． Partly，this is due to the fact that climatic change is moving from a pure topic of atmospheric science and evolving into an issue associated with carbon reduction，carbon tax and other national interests． Since having been highly economy-linked，the issue may inevitably deviate from pure science discussion and leave room for unfairness to step in． Based on in-depth review and analysis，we come to conclusions as follows: 1) Because rapid urban development in last century had affected temperature measurements，the heating island effect should be considered to avoid the overestimation of global warming; 2) The contributing factors，human or natural ones，of the warming during last century remain uncertain，so the warming rate may be 0. 4 ℃ or even lower，if the heating island effect is corrected，; 3) At 10 000-year time scale，global climate is in its cooling trend，in contrast to the warming at 100-year time scale，and the latter can be explained more reasonably as one of secondary fluctuations of the former; 4) Either in the past or at present，the change of atmospheric CO₂ concentration has always lagged behind that of temperature． In other words，temperature drives CO₂ but not vice versa．