From the examination of core samples taken from glaciers (which carry within them thousands of years of climatological data), paleoclimatologists have found evidence of a positive correlation between concentrations of carbon dioxide and global temperatures. "But whenever the natural concentration of carbon dioxide reaches a certain threshold, it falls again," says Wei Kuo-yen, a professor of paleoceanography and micropaleontology in NTU's geosciences department.
古氣候學者從累積千萬年氣候訊息的冰川鑽探結果，也證實古來二氧化碳濃度就與地球溫度成正比，「自然界二氧化碳的增加總在到達一個臨界點後就降下來，」研究海洋微化石的台大地質所教授魏國彥說。