Weather consists of those meteorological events, such as rain, wind and sunshine, which can change day-by-day or even hour-by-hour. Climate is the average of all these events, taken over a period of time. The climate varies over different parts of the world. Climate is usually defined as the average of the weather over a 30-year period. It is when that average changes significantly that people start thinking the climate might be changing. In this article, the author summarises the current state of knowledge about climate change. (Contains 7 figures.)