In recent decades, the role of greenhouse gases on climate change since human industrialization has been emphasized in floods of papers and books. Here, we review the causes of climate change during the 20th century, and some new evidences for decoupling of atmospheric greenhouse gases and climate from ice cores and geological records, and then point out some important issues needed to be further studied, such as the age difference between ice and young air it encloses, and the correlation between the Sun and the Earth climate.