World Temperatures Through the Ages
How did the Earth's climate arrive at its current state and how do scientists delve into the secrets of our planet's past?
The layers of ice laid down each year in Antarctica and Greenland store a record of the Earth's climate. Bubbles of air trapped in the ice as it froze can be analysed to give details on temperature at the time it froze, and on atmospheric concentrations of gases.
The oldest ice core so far extracted belongs to the European Project for Ice Coring in Antarctica (Epica). It allows scientists to look back 800,000 years.
Over time, the Earth's orbit around the Sun varies slightly. This changes the amount of solar energy reaching the Earth's surface, alternately warming and cooling the planet's surface.
In a warming phase, greenhouse gases such as carbon dioxide are released and amplify the warming - increasing the natural greenhouse effect. They are stored again when an ice age starts.
So over this period, we see temperature and carbon dioxide concentrations changing in step, in cycles lasting about 100,000 years.
About 10,000 years ago, the Earth emerged from its most recent ice age. Agriculture developed, and the extra food supported a growing global population.
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