These days there is much concentration on the issue of climate change. The main debate now is focused on the issue of Global Warming and the current warming of the Earth's climate being due to human activities. However, research of geological records going back millions of years, have indicated that there have been a large number of variations in the Earth’s climate. A variety of natural factors have caused this, including the Earth’s orbit, changes in the sun, volcanoes and CO2 levels.