Mark Pagani : CO2 levels in atmosphere undergo major changes . He said research on the past shows the dangers of high levels of greenhouse gases . Well , a 1˚C ( 1.8˚F ) global temperature increase is close to what we 've already measured , but full warming is not expressed overnight or even over decades because the world is mostly a cold ocean that helps ameliorate immediate warming by taking up heat . Today 's CO2 levels comparable to time when Greenland had little land , which was several feet higher . Others : With more CO2 , we hark back to when crocodiles and sub - tropical plants inhabited the poles .
Mark Pagani : CO2 levels in atmosphere undergo major changes . He said research on the past shows the dangers of high levels of greenhouse gases . Today 's CO2 levels comparable to time when Greenland had little land , which was several feet higher . Others : With more CO2 , we hark back to when crocodiles and sub - tropical plants inhabited the poles .