Our climate has always changed; it has fluctuated between cold times (glacials) and warm times (interglacials).
The millions of years prior to today can be separated into geological periods. The last 2.6 million years is known as the Quaternary geological period. The graph below shows how the global air temperature has fluctuated of the last 5.5 million years – clearly the temperature has been warmer than today, as well as colder than today. It is important to recognise the temperature has fluctuated constantly and that before the Quaternary geological time period started, the temperature has higher than it is today.
Scan of Fig.1 p.42
The graph below shows how temperature has changed over the last 400,000 years. Note that the temperature is normally lower than it is today and that the interglacials do not last particularly long – our current interglacial only started about 10,000 years ago.
Scan of Fig.2 p.42
The graph below shows how the global air temperature has changed over the last 150 years. It shows that the temperature has increased by about 1°C.