Antarctic ice may reveal much more about ancient climates.

Researchers hope the discovery of ancient Antarctic ice will give them access to crucial information about carbon dioxide levels during a period when ice ages were much more frequent.

A team of scientists, including Tas van Ommen from the Hobart-based Australian Antarctic Division, say they have identified the most likely location of ice dating from 1.5 million years ago, almost double the oldest ice cores so far extracted, at 800,000 years.

In a paper published in the Climate of the Past journal, the researchers say they have narrowed down a region of the East Antarctic Ice Sheet as likely to contain the ice, possibly as much as 2.5 kilometres below the surface.

“One of the key things is that the ice will give us the carbon-dioxide levels [from that period]," Dr van Ommen said.

That information would allow scientists to improve their understanding of how the global climate has changed in the past.

For the past 900,000 years, ice ages have come and gone at a fairly regular cycle of about every 100,000 years, Dr van Ommen said.

By contrast, before that period, the rate was more like an ice age about every 40,000 years, he said.

"By understanding how carbon dioxide actually affects the sensitivity of the climate, we'll have a better idea of future changes are going to be in the long term," Dr van Ommen said.

The paper, “Where to find 1.5 million-year-old ice”, notes the frequency of ice ages appears to have changed during what has been dubbed the mid-Pleistocene Transition (MPT ) covering the period between 900,000 and 1.2 million years ago.

It said that, while rough estimates of the level of carbon dioxide in the atmosphere can be made for the period from other sources, such as marine sediments, “an ultimate answer about the role of greenhouse gas climate forcing can only be derived from the atmospheric record archived in an Antarctic ice core covering this time interval”, the paper said.

(Please note: An earlier version of this article made incorrect references to the timing of the ice age cycles.)