The ice cover of earth is inherently unstable. If the earth gets colder, the ice formed becomes both whiter and more extensive. This in turn increases the albedo (reflectivity) of the earth, making it colder still in a vicious circle. Conversely if the earth warms, from increased CO₂ levels, the ice formed becomes both greyer and less extensive. This in turn decreases the albedo of the earth, making it warmer still in a vicious circle.
~ Roedy (born: 1948-02-04 age: 61)