*Written by Heiko Goelzer from the Bjerknes Centre and NORCE and Erik Mulder from the University of Groningen.*

There is geological evidence that the Earth was fully glaciated during several periods around 700 million years ago and attained a so-called Snowball Earth state.

Additional support for this idea has come from climate models of varying complexity that show transitions to Snowball Earth states under changes in solar radiation. In our new study we have used a novel, fully-implicit Earth System Model of intermediate complexity to study such transitions.

The novelty of this work is the application of a newly developed, fully-implicit Earth System Model, which allows to look at the behaviour of the Earth as a dynamical system. Implicit means that the system is not evolving step-by-step forward in time, like classic computer models of the Earth, but that it solves every numerical constraint that arises from the physics simultaneously; it solves the ‘matrix’ of the Earth system.

This can be a very useful tool to map out large-scale equilibria and explore their stability properties in a rigorous fashion. Here it is applied to determine transitions in and out of Snowball Earth states and to compute the characteristic patterns of unstable growth between these states.

## Reference

Mulder, T. E., Goelzer, H., Wubs, F. W., and Dijkstra, H. A.: Snowball Earth Bifurcations in a Fully-Implicit Earth System Model, *International Journal of Bifurcation and Chaos*, 31.