For example, if the Earth got cold enough, the encroachment
of snow and ice toward low latitudes (where they have more sunlight to reflect per unit area), depending on the meridional temperature gradient, could become a runaway feedback — any little
forcing that causes some cooling will cause an expansion
of snow and ice toward lower latitudes sufficient to cause so much cooling that the process never reaches a new equilibrium — until the snow and ice reach the
equator from both
sides, at which point there is no more area for snow and ice to expand into.