  In ecology, climate and other fields, (sub)systems have been identified that
can transition into a qualitatively different state when a critical threshold
or tipping point in a driving process is crossed. An understanding of those
tipping elements is of great interest given the increasing influence of humans
on the biophysical Earth system. Complex interactions exist between tipping
elements, e.g. physical mechanisms connect subsystems of the climate system.
Based on earlier work on such coupled nonlinear systems, we systematically
assessed the qualitative long-term behaviour of interacting tipping elements.
We developed an understanding of the consequences of interactions on the
tipping behaviour allowing for tipping cascades to emerge under certain
conditions. The (narrative) application of these qualitative results to
real-world examples of interacting tipping elements indicates that tipping
cascades with profound consequences may occur: the interacting Greenland ice
sheet and thermohaline ocean circulation might tip before the tipping points of
the isolated subsystems are crossed. The eutrophication of the first lake in a
lake chain might propagate through the following lakes without a crossing of
their individual critical nutrient input levels. The possibility of emerging
cascading tipping dynamics calls for the development of a unified theory of
interacting tipping elements and the quantitative analysis of interacting
real-world tipping elements.
