During the Palaeolithic period there were enormous changes in climate. At one extreme ice-sheets covered Britain as far as the Thames Valley, creating a polar desert. Warmer periods had temperatures similar to the present-day. Since people first reached Britain, at least 500,000 years ago, there have been five cold periods or Ice Ages, with six intervening warm phases. Much of the time the climate would have been between these extremes, with cold winters and cool summers.

The changes in climate had a major effect on the animal and plant life. During the cooler periods open, treeless landscapes would have been inhabited by animals such as musk-ox, reindeer and woolly mammoth. Deep forest would have covered the landscapes during warmer periods, with river valleys kept more open by the grazing and trampling of large mammals such as straight-tusked elephant, rhinoceros and at times hippopotamus.

The varying climate also affected the human presence in Britain. At times of extreme cold, temperatures would have been too severe for people to survive. This would have been made more difficult by the lack of animal and plant resources.