Tj. Crowley et al., SNOWLINE INSTABILITY IN A GENERAL-CIRCULATION MODEL - APPLICATION TO CARBONIFEROUS GLACIATION, Climate dynamics, 10(8), 1994, pp. 363-376
For over twenty years it has been known that energy balance models (EB
Ms) with snow-albedo feedback are characterized by unstable behavior i
n some areas of parameter space. This behavior leads to rapid changes
in snow area due to small changes in forcing, and has been termed the
small ice cap instability (SICI). It has never been clarified whether
this behaviour reflects a real feature of the climate system or a limi
tation in EBMs. In this study we demonstrate that evidence for similar
unstable behavior can also be found in an atmospheric general circula
tion model (GCM), using a realistic set of boundary conditions for the
Carboniferous (300 Ma), one of the most extensive periods of glaciati
on in Earth history. When solar luminosity is sequentially lowered to
near values appropriate for the Carboniferous, there is a discontinuou
s increase in summer snow area. The instability occurs in approximatel
y the same area of parameter space as one previously found in an EBM.
Analysis of selected fields indicates that the circulation is primaril
y affected in the area of snow increase; far-field effects are minimal
. There is good agreement between model-generated summer snowcover and
one reconstruction of Carboniferous ice cover. Although more work is
required on this topic, our results provide increased support for the
possibility that the snowline instability represents a real feature of
the climate system, and that it may help explain some cases of glacia
l inception and abrupt transitions in Earth history.