The findings could help us understand more about rapid climate changes, scientists said.
Until now temperatures during the warm periods between ice ages - known as interglacials - were thought to be only slightly warmer than those of the present day, British Antarctic Survey (BAS) scientists explained.
But the findings, published this week in journal Nature, show brief spikes in temperature, which recur roughly every 100,000 years and last a few thousand years, seem to have been a lot warmer.
The new findings could help scientists predict how any melting of ice in the future could affect sea levels.
Ice core scientist Eric Wolff, of BAS, is a world-leading expert on past climate. He said: ''During the last warm period, about 125 000 years ago, sea level was around five metres higher than today.
''If we can pin down how much warmer temperatures were in Antarctica and Greenland at this time, then we can test predictions of how melting of the large ice sheets will contribute to sea level rise.''
Ice cores from east Antarctica contain the oldest drilled ice on Earth, and provide a unique record of past climate, the study said.
Louise Sime from BAS, lead author of the report, said: ''We analysed Antarctic ice cores to look at climate during past warm periods and were surprised to find relatively high Antarctic temperatures during some spikes.
''We don't yet know what caused these peaks, but we would like to be sure we haven't missed anything important about how Antarctica is set to change in a warming world.''
Analysis of the ice cores has revolutionised our understanding of how Antarctic climate has varied in the past, the study added.
Julia Tindall, an author of the paper from the University of Bristol, added: ''It is quite difficult to reconstruct temperatures from long ago. Although it is generally accepted that the climate was warmer 125,000 years ago, our results suggests it was much warmer than previously thought. It will be interesting to see if other studies agree with our findings.''