Karlsruhe Institute of Technology: Clouds have played important roles in climate history

Were the Earth’s oceans completely covered with ice in the Cryogenium – around 700 million years ago – or was there an ice-free water belt around the equator in which sponges and other life forms could survive? A research team from the Karlsruhe Institute of Technology (KIT) and the University of Vienna has now been able to show in global climate models that a climate condition with a water belt is rather unlikely and therefore not a reliable explanation for the survival of life in the cryogenium. The reason for this is the uncertain influence of clouds on the climate at that time. The team presents the results of the study in the journal Nature Geoscience . 

From space, Earth might have looked like a large snowball during the global ice ages in the Cryogenium. Geosciences therefore refer to this assumption of a closed sea ice cover, which has been established in research, as the Snowball Earth Theory. In particular, it is still unclear how sponges – of which fossil finds bear witness – could have survived in the very cold snowball earth climate. Therefore, some researchers have proposed an ice-free water belt around the equator as an alternative theory.

Living despite probably icy oceans

Climate researchers from KIT, together with colleagues from the University of Vienna, have investigated the climatic conditions during the cryogenium using global climate models and an idealized energy balance model. They expected to find a climate state with a water belt in the simulated scenarios in order to investigate under which conditions it remains stable. “We were surprised that this condition is not shown to be robust in the models,” says Christoph Braun from the Institute for Meteorology and Climate Research – Department Tropospheric Research (IMK-TRO) of KIT. Life in the Cryogenium was thus probably exposed to the harsh evolutionary conditions of globally icy oceans.

The study provided new insights into the role of clouds: “Clouds and their radiation reflection are important for the stability of a water belt state – this strong influence was previously unknown,” emphasizes the doctoral student and first author of the study. With the cloud-reflectivity mechanism proposed in the publication, the results of previous studies could be reinterpreted and possibly linked to form a more coherent picture.

Clouds make it difficult to look into the climate past

“With the global climate models and an idealized climate balance model, we can show the influence of the reflectivity of clouds and explain the underlying processes,” says Braun. “However, it is not possible to assess how strong the reflectivity of the clouds in the Cryogenium was, because the uncertainty in the representation of clouds in global climate models is large.” depends, among other things, on the type and quantity of the aerosols acting as ice nuclei. These processes take place on a millimeter scale, while the calculation grids of the models have so far been in the order of more than 100 kilometers. The results show that clouds are crucial to predict climate changes and to understand the dynamics of geological glaciations. “Clouds not only make it difficult for us to look into the future, but also into the past,” says Braun.

Assessing the habitability of planets outside our solar system

The researchers’ findings could also be useful in the future to assess whether planets outside our solar system are habitable. “This becomes interesting, for example, when future observations by the James Webb Space Telescope enable views of clouds in the atmospheres of extrasolar planets,” says Braun. The KIT researchers carried out the simulations on the Mistral high-performance computer of the German Climate Computing Center in Hamburg. “As a next step, we started simulating clouds under the climatic conditions of the Cryogenium on finer computational grids. This allows us to investigate whether and how the uncertainty associated with the clouds can be reduced,” says Braun.

The German Research Foundation (DFG) has funded the research project completed in May 2022 within the DFG project “Is the Jormungand hypothesis a possible alternative explanation for the Neoproterozoic Ice Age?” for three years with a total of 202,000 euros. The atmosphere model ICON was used for the simulations. KIT is involved in its development in a consortium with the Max Planck Institute for Meteorology and the German Weather Service.