Ice cores are collected from ice sheet from the polar ice caps of Antarctica and Greenland, and from high mountain glaciers around the world.
An ice core is a sample from the incremental buildup of annual layers of snow over many years.
These records provide valuable information about the atmospheric environment at the time the bubbles were trapped in the ice.
The chemical composition of these ice cores, especially the presence of hydrogen and oxygen isotopes, provides vital information on climate variability over time.
For example, ice cores also contain an abundance of climate information such as bubbles of atmospheric gases like carbon dioxide and methane, wind-blown dust, volcanic ash and radioactive substances like Beryllium 10 that provide information about past solar cycles.
The longest ice core, drilled by a team of European scientists (EPICA), comes from Antarctica and covers the past 800,000 years.
Data from the upper sections of ice cores from high accumulation areas like Law Dome in Antarctica have been studied by the Australian Antarctic Division.
They have been found to provide a fine scale perspective of the Southern Hemisphere climate variability over the past 750 years.