Light surfaces reflect more heat than dark surfaces. This is called the albedo effect. When the earth's temperature dropped because of its position in orbit around the sun, and the tilt of the axis, the ice sheets grew. This in turn caused more heat to be reflected and the ice sheets to expand further. Professor Iain Stewart uses coloured and plain ice cubes to demonstrate the albedo effect and glaciologist Croll's theory.
Use in conjunction with study of the Earth's changing orbit to explain the cyclical nature of climate changes over the last 2 million years. Students could produce annotated maps or diagrams to show how the albedo effect causes ice caps to increase in size. Students could also model the opposite effect showing increasing temperature can decrease the size of ice caps and glaciers, increasing absorption and in turn resulting in further temperature increase.