In reply to Roger Jones, April 18, the climate of the earth moves regularly from warm to cool over periods of several thousands of years.

During the age of the dinosaurs the earth was very hot and animals lived comfortably at the South Pole.

After that there have been a number of ice ages when the polar caps expanded and the earth became very cold.

The causes of these changes in climate are not fully understood.

But what is understood is that they happen at regular intervals and are perfectly natural.

Noel Gardner, Carlisle Avenue, Swindon