Wladimir Köppen Award 2023

30 September 2024, by Miriam Frieß

Photo: Bettina Diallo / MPI-M

In recognition of his outstanding dissertation, geophysicist Dr. Lennart Ramme has been awarded the Cluster of Excellence CLICCS’s 2023 Wladimir Köppen Prize. According to the jury, in his work the researcher from the Max Planck Institute for Meteorology “lays the basis for investigating the extreme dynamics of the Earth’s climate system, which until recently was considered impossible.”

From ice and snow to a supergreenhouse climate

Over 635 million years ago, in the late Neoproterozoic, our entire planet was covered with ice, a situation also referred to as the “snowball Earth.” However, due to volcanic activity, CO₂ accumulated in the atmosphere for millions of years. The climate gradually grew warmer until the ice sheets began melting and a positive feedback effect set in: as more ice was lost, the Earth’s surface became darker and absorbed more sunlight, which in turn caused it to warm even more. In this way, a massive climatic change – from the snowball Earth to a supergreenhouse climate – took place in the course of just a few thousand years.

In his dissertation, Lennart Ramme investigated our planet’s status after the snowball Earth phase, in particular, exchanges of carbon dioxide between the ocean and atmosphere. For his work, he applied a complex 3D computational model, while also considering further factors, like the ocean’s pH value, which affected the carbon budget at the time. He was able to show that the prevalent conditions might have been different than previously assumed.

A glimpse of the past

Once the ice had melted, the less dense meltwater initially formed a layer atop the ocean’s saltwater, effectively preventing exchanges between the surface water and the ocean depths. Ramme determined that this layering ended much sooner than past calculations had estimated – which also had an effect on the ocean’s carbon budget and the formation of characteristic carbonate rock.

In turn, due in part to the more rapid formation of carbonate rock, the seawater couldn’t absorb as much CO₂. As such, Ramme believes the ocean – which at first was still completely covered by ice – may have had an alkaline pH value. In the comparatively short time in which the layering of fresh- and saltwater in the ocean remained in place, the first layers of carbonate rock formed, driven by the rapid warming and the resumption of biological activity. This process removed not just carbon but also other chemical elements from the water, causing its pH value to ultimately decline and, possibly, even causing the ocean to release CO₂ back into the atmosphere.

Lastly, our planet’s first lifeforms also played a major part in the oceanic carbon budget: as the climate warmed following the snowball Earth phase, and land-based nutrients found their way into the ocean, algae and other small lifeforms thrived and absorbed carbon. When they died, they sank to the seafloor, transporting the carbon to the deep sea like a “biological carbon pump.”

Ramme’s thesis comprehensively assesses these various factors and offers insights into how the first organisms were able to survive the transition from the snowball Earth to a supergreenhouse climate. His conclusion: at the end of the snowball Earth, temperatures weren’t nearly as high as the calculations to date have indicated. Rather, he considers a global mean temperature of just 30 degrees to be plausible. Unlike in the hot equatorial climate zones, temperatures at the poles may have been predominantly temperate, making it possible to survive the otherwise extreme conditions.