During the Cretaceous the global climate was quite different from today: no indications for long-lived glaciation have been identified and the temperature differences between poles and equators as well as oceans and continents were much smaller. Atmospheric CO2 was much higher than today but the presently observed rise in pCO2 has led to concern that global climate may return to the ‘uninhabitable’ state of the Cretaceous. Although discussions and studies have been on-going for a number of years the trigger for the transition from the Cretaceous greenhouse to the Cenozoic icehouse has still not been identified without doubt.

A decline in atmospheric pCO2 seems to be an important driver of Cretaceous-Paleogene/Neogene climate changes in the Southern Ocean but the opening of gateways and subsequent migration of continents also has had a profound effect on the regional climate change and oceanography . Although the theory of declining CO2 levels resulting in strong cooling at the Eocene-Oligocene boundary is supported by reconstructions of Cenozoic atmospheric CO2 and modelling studies  it does not answer the question why atmospheric CO2 strongly declined during the Cenozoic. Geological evidence  as well as modelling studies on the other hand challenge the gateway theory. Uplift of large mountains and associated increased weathering have also been discussed to have had an influence on global climate but it is difficult to estimate how much atmospheric CO2 was removed during the process. A fourth theory discusses modified insolation patterns and seasonality which suffers from uncertainties in the used tuned age model.


Atmospheric pCO2 and global temperature as reconstructed for the last 70 million years.