Scientists have identified regions in Antarctica that could store information about Earth's climate and greenhouse gases dating back to 1.5 million years, twice as old as ice core drilled to date.
By studying the past climate, scientists can understand better how temperature responds to changes in greenhouse-gas concentrations in the atmosphere.
This, in turn, allows them to make better predictions about how climate will change in the future.
"Ice cores contain little air bubbles and, thus, represent the only direct archive of the composition of the past atmosphere," said Hubertus Fischer, professor at the University of Bern in Switzerland and lead author of study.
A 3.2-km-long ice core drilled almost a decade ago at Dome Concordia (Dome C) in Antarctica revealed 800,000 years of climate history, showing that greenhouse gases and temperature have mostly moved in lockstep.
Now, an international team of scientists wants to know what happened before that.
At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago.
"The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet," said Fischer.
Earth's climate naturally varies between times of warming and periods of extreme cooling (ice ages) over thousands of years.
Before the transition, the period of variation was about 41 thousand years while afterwards it became 100 thousand years.
"The reason for this change is not known," Fischer said.
Climate scientists suspect greenhouse gases played a role in forcing this transition, but they need to drill into the ice to confirm their suspicions.
"The information on greenhouse-gas concentrations at that time can only be gained from an Antarctic ice core covering the last 1.5 million years. Such an ice core does not exist yet, but ice of that age should be in principle hidden in the Antarctic ice sheet," said Fischer.
