Climate change refers to how the average climatic conditions of the planet vary over time. At some point's in the history of the earth, the climate has been comparatively warmer and at some points it has been much colder. The history of the earth is divided into periods. The Quaternary period is the last 1.8 million years of the world's history. During this period, there has been many times where the temperature of the world has dropped. During these drops in temperature large continental ice sheets covered much of the Northern Hemisphere. When this happens, it is known as a glacial period or ice age. When the ice sheet melts due to warmer temperatures, this is known as an inter-glacial period. The last glacial period was between approximately 120,000 and 11500 years ago. Since this point, the earth has been in an interglacial period which is known as the holocene. There is still some glacial cover in parts of the world e.g. Greenland and Antarctica.
