A new study of Antarctica's past climate reveals that temperatures during the warm periods between ice ages (interglacials) may have been higher than previously thought. The latest analysis of ice core records suggests that Antarctic temperatures may have been up to 6°C warmer than the present day.

The findings, recently reported by scientists from the British Antarctic Survey (BAS), the Open University and University of Bristol in the journal Nature could help us understand more about rapid Antarctic climate changes.

Previous analysis of ice cores has shown that the climate consists of ice ages and warmer interglacial periods roughly every 100,000 years. This new investigation shows temperature 'spikes' within some of the interglacial periods over the last 340,000 years. This suggests Antarctic temperature shows a high level of sensitivity to greenhouse gases at levels similar to those found today.

Lead author Louise Sime of British Antarctic Survey said, "We didn't expect to see such warm temperatures, and we don't yet know in detail what caused them. But they indicate that Antarctica's climate may have undergone rapid shifts during past periods of high CO2."

During the last warm period, about 125,000 years ago, sea level was around 5 metres higher than today. Ice core scientist Eric Wolff of British Antarctic Survey is a world-leading expert on past climate. He said, "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 may contribute to sea level rise."

Notes:
Ice cores are unique climate records, allowing scientists to investigate climate changes over hundreds of thousands of years. The Earth's oldest ice is found in East Antarctica. The three oldest existing ice cores were drilled at Dome C, Dome F and Vostock. The longest ice core -- at 3,650 metres -- comes from Vostock, but the oldest ice core, drilled by the European Project for Ice Coring in Antarctica (EPICA) team, contains a climate record stretching back 800,000 years. Analysis of the ice cores has revolutionized our understanding of how Antarctic climate has varied in the past. Information from ice cores is vital for testing and improving the computer models used to predict future climate.

Interglacials -- recur roughly every 100,000 years between ice ages. The present warm period began around 10,000 years ago and has been relatively stable.

Direct sea level measurements based upon coastal sedimentary deposits and tropical coral sequences have established that global sea level was higher than present during the last interglacial (~125,000 years ago) by approximately 4 to 6 m. This indicates that the Greenland and Antarctic ice-sheets were smaller than during the present day.

The authors analysed 340,000 years of oxygen and hydrogen isotope data from three ice core sites across East Antarctica, alongside isotope-enabled general circulation model results.

Journal Reference:
1. Sime et al. Evidence for warmer interglacials in East Antarctic ice cores. Nature, 2009; 462 (7271): 342 DOI: 10.1038/nature08564

(ScienceDaily*, 19/11/2009)

*Adapted from materials provided by British Antarctic Survey.