The classic ice-albedo positive feedback in response to global warming (also see glossary for a detailed definition of ”albedo”). Increased temperature leads to increased melting of polar ice which, in turn, leads to a decrease in albedo. Since albedo is the reflectivity of the Earth’s surface, its decrease leads to even more warming. The resulting correlation of the loop is reinforcing (positive sign). Generally, such positive correlations (also called positive feedbacks) will lead to instabilities.