The ice albedo effect is a positive feedback mechanism that causes global temperatures to progressively get colder and the albedo of the Earth to continue to increase. The ice albedo mechanisms starts with global temperatures cooling due to some factor such as less solar output, Milankovitch cycle cooling, asteroid impact, intense volcanic eruptions into the stratosphere, etc. Once global temperatures begin to cool, the polar areas begin to experience a buildup of ice (ice sheets and glaciers enlarge). The albedo comes into play by ice having a high albedo which means it is good at reflecting solar radiation. With increased solar radiation reflected away, this contributes to temperatures cooling. This cooling helps build up more ice which in turn produces even more cooling. This is the positive feedback mechanism at work. In an extreme case, this would continue until the entire earth is covered in ice (known as snowball earth). Mechanisms that produce global warming would have to initiate to reverse this process. While the Earth may not have completely been covered with ice, it is likely the ice did develop into fairly low latitudes. At the very least, ice ages resulted that resulted in deep ice covering significant portions of continents in the high and middle latitudes.