The Earth climate during the last 2 million years has been dominated by shifts between colder periods, known as Ice Ages or glacials, and warmer periods, known as interglacials. Whilst Ice Ages have tended to last for up to 100,000 years, the intervening interglacial periods have usually been much shorter in duration, at around 10,000 years in length.
The last interglacial occurred about 120,000 years ago. Today, the Earth's climate is again within an interglacial period, although the orbital theory of climate change, which explains the glacial-interglacial transitions, predicts that we may be coming towards its end. Indeed, during the 1960s, many scientists suggested that the observed fall in Northern Hemisphere temperatures at that time reflected the gradual onset of a new Ice Age. Since then however, fears of global warming as a result of man-made greenhouse gas pollution have dominated the environmental agenda. Scientists revisiting the instrumental records of global surface temperature, including both Northern and Southern Hemisphere records, realised that over the whole of the 20th century, the Earth had actually warmed. Whether global warming will only postpone the end of the current interglacial or lead to a completely new climatic regime is very hard to predict.