COOLER ESTIMATES OF CRETACEOUS TEMPERATURES

THE Creataceous period is thought to have been warmer than the present (1-3), with higher concentrations of atmospheric greenhouse gases such as carbon dioxide(4). It has therefore been suggested(5) that this ti me period could be used by modellers as an analogue for future climate change. But the Cretaceous Equator-to-Pole temperature gradient was f latter than today's, leading some to suggest that Cretaceous climate a rose from a combination of factors, with higher atmospheric carbon dio xide concentrations leading to general warming, and other factors, suc h as increased ocean heat transport, leading to flattening of the lati tudinal temperature gradient. Here we report new records of ocean pala eotemperature for Cenomanian sites in the Atlantic and Pacific oceans which, together with a re-evaluation of published data, cast doubt on the idea that the Cretaceous period was generally warmer. These data c onfirm that the latitudinal temperature gradient was flatter, but sugg est that the global mean temperature,vas much cooler than previously b elieved, with minimum mean equatorial temperatures close to present va lues and polar temperatures close to 0 degrees C. In the light of thes e findings, the climatic role of atmospheric carbon dioxide in determi ning Cretaceous climate is unclear, suggesting that the Cretaceous can not be used as an analogue for future climate change.