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Professor Iain Stewart explains how the temperature of the earth is affected by its orbit round the sun, and the tilt of its axis. This was a theory put forward by James Croll. Professor Stewart draws the changing orbit of the earth around the sun on a sandy beach. He explains why this causes temperatures to fall and how this can be exaggerated by the changing tilt of the earth.

Use to introduce the concept of Quaternary climate change, either to inform discussion of current climate change issues or to explain the cyclical nature of glacial periods. Looking at timelines of global temperature will help students appreciate that glacial features may develop over several glacial periods and that the differing extent of these periods will result in changes to the features they produce, such as the position of glacial deposits.