Toward understanding Cretaceous climate—An updated review

New data and ideas are changing our view of conditions during the Cretaceous. Paleotopography of the continents was lower than originally thought, eliminating the ‘cold continental interior paradox’ of fossils of plants that could not tolerate freezing occurring in regions indicated by climate models to be well below freezing in winter. The controversy over the height of Cretaceous sea levels has been resolved by knowledge of the effects of passage of the subducted slab of the Farallon Plate beneath the North American crust. The cause of shorter term sea level changes of the order of 30 to 50 meters is not because of growth and decay of ice sheets, but more likely the filling and release of water from groundwater reservoirs and lakes although there may have been some ice in the Early and latest Cretaceous. Carbon dioxide was not the only significant greenhouse gas; methane contributed significantly to the warmer climate. Suggestions of very warm tropical ocean temperatures (>40°C) have implications for the nature of plant life on land limited by Rubisco activase. The land surfaces were much wetter than has been thought, with meandering rivers and many oxbow lakes providing habitat for large dinosaurs. A major rethinking of the nature of conditions on a warmer Earth is underway, and a new suite of paleoclimate simulations for the Cretaceous is needed.