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 time period could be used by modellers as an analogue for future climate change. But the Cretaceous Equator-to-Pole temperature gradient was flatter than today's, leading some to suggest that Cretaceous climate arose from a combination of factors, with higher atmospheric carbon dioxide concentrations leading to general warming, and other factors, such as increased ocean heat transport, leading to flattening of the latitudinal temperature gradient. Here we report new records of ocean palaeotemperature 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 confirm that the latitudinal temperature gradient was flatter, but suggest that the global mean temperature,vas much cooler than previously believed, with minimum mean equatorial temperatures close to present values and polar temperatures close to 0 degrees C. In the light of these findings, the climatic role of atmospheric carbon dioxide in determining Cretaceous climate is unclear, suggesting that the Cretaceous cannot be used as an analogue for future climate change.