EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reconstructing the evolution of ice sheets, sea level and atmospheric CO2 during the past 3.6 million years

Tijn Berends1, Bas de Boer2, and Roderik van de Wal1
Tijn Berends et al.
  • 1Utrecht University, Institute for Marine and Atmospheric Research Utrecht, Physics and Astronomy, Utrecht, Netherlands (
  • 2Earth and Climate Cluster, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands

Understanding the evolution of, and the interactions between, ice sheets and the global climate over geological time is important for being able to constrain earth system sensitivity. However, direct observational evidence of past CO2 concentrations only exists for the past 800,000 years. Records of benthic d18O date back millions of years, but contain signals from both land ice volume and ocean temperature. In recent years, inverse forward modelling has been developed as a method to disentangle these two signals, resulting in mutually consistent reconstructions of ice volume, temperature and CO2. We use this approach to force a hybrid ice-sheet – climate model with a benthic d18O stack, reconstructing the evolution of the ice sheets, global mean sea-level and atmospheric CO2 during the late Pliocene and the Pleistocene, from 3.6 Myr ago to the present day. The resulting reconstructions of CO2 and sea level agree well with the ice core record and different sea-level proxies, indicating that this model set-up yields useful information for colder-than-present climates. For the warmer-than-present climates of the Late Pliocene, different proxies for both CO2 and sea level are contradictory, making model validation difficult. During the early Pleistocene, 2.6 – 1.2 Myr ago, we simulate 40 kyr glacial cycles with CO2 ranging between 270 – 280 ppmv during interglacials and 210 – 240 ppmv during glacial maxima. After the Mid-Pleistocene Transition (MPT), when the glacial cycles change from 40 kyr to 80/120 kyr cyclicity, these values change to 260 to 280 ppmv during interglacials, and 180 – 200 ppmv during glacial maxima.

How to cite: Berends, T., de Boer, B., and van de Wal, R.: Reconstructing the evolution of ice sheets, sea level and atmospheric CO2 during the past 3.6 million years, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8762,, 2020.