Climate change refers to changes in the Earth's long-term weather patterns. Some changes in climate occur naturally; gradual temperature fluctuations over thousands of years are a natural part of the Earth's climate. The Ice Age, for example, was a period of time when our climate was much cooler than it is now. However, human activities can also cause changes;the term 'climate change' is generally used to describe a more rapid, human-caused increase in the Earth's average temperature.