Understanding past climates to better predict future changes

Human-induced global warming presents humanity with many problems and opportunities (see IPCC website), but predominantly with many uncertainties about how global warming is going to affect the Earth’s system in the near future. Palaeoclimatology (paleoclimatology in American English), i.e. the study of past climates, aims to understand climate change of the (geological) past to draw lessons about how the climate system can behave under boundary conditions (such as land-ice volume distributions, atmospheric CO2 levels) different than those of today. Often, comparable conditions to those of the distant past are also projected for the future. One video I always find very compelling in showing why we want to understand the natural behaviour of the climate system is this one:

It shows a complication of CO2 data of the past 800,000 years of Earth history, based on instrumental and ice-core records. The main message is that current CO2 levels of >400 parts per million (ppm) are unprecedented for the time-period covered by these records. The enormous ice volume changes that occured during the most recent ice ages, were thus concurrent with, and largely caused by, CO2 changes between 185 and 278 ppm, all below the present-day CO2 value.

We thus need to go further back in time than the oldest remaining ice on the Earth to find past climates that did experience CO2 levels more similar to those of the present day and near future. To do so, climate scientist study marine sediments and terrestrial rock outcrops. The time period between 34 and 17 million years ago forms an interesting case study, because CO2 values varied between 800 and 400 ppm (these estimates are based on several reconstruction methods), and during this time period there was no ice on the North Pole. Therefore, we can study the dynamics of the Antarctic ice sheet in great detail.


Cibicides (Cibicidoides) mundulus is a benthic (i.e. sea-bottom dwelling) foraminifer that builds a calcite shell (pictured). These fossilised, single-celled, microscopic shells are often used in palaeoclimatic and palaeoceanographic studies because the oxygen isotope values of the calcite is a function of bottom water temperatures and global land-ice volumes. This specimen is ~200 micrometer wide (smaller than a grain of sand).

Climate dynamics during Earth’s Cenozoic icehouse

Oligocene-Miocene climate and Antarctic ice sheet evolution

The evolution of the early Cenozoic cryosphere and climate system has been my main research focus during the past 10 years. This work has been aimed at better documenting and understanding the unipolar icehouse of the Oligocene and early Miocene (between 34–17 million years ago), which is characterised by the first ice ages on Antarctica. To this purpose, I have generated a 13 million year long high-resolution benthic foraminiferal stable isotope stratigraphy from South Atlantic Site 1264, and I have collaborated on a similar stratigraphic data set from equatorial Pacific Site U1334. Several of my current research efforts are geared towards obtaining better constraints on the boundary conditions that triggered the recurrent glaciations and subsequent phases of ice-sheet instability during the Oligo-Miocene.

Evolution of Oligo-Miocene CO2, ice volume and glacial cycle asymmetry. Surprisingly, ice volume is lower, when CO2 is lower and glacial cycle asymmetry is higher. This finding is currently not fully understood (see Liebrand et al., PNAS, 2017).