Nature doi:10.1038/nature06015 (2007)

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Antarctic climate change has lagged behind changes in northern hemisphere summer sunshine over the past 360,000 years, finds a new study. This suggests that CO2 levels amplify rather than trigger the end of ice ages.

A team led by Kenji Kawamura at Tohoku University in Japan and the Scripps Institution of Oceanography in California dated ice cores using the oxygen-to-nitrogen ratios of trapped air in a new method to establish the order in which changes in CO2, Antarctic temperature and sunshine occur at the end of an ice age. Although other ice-core dating techniques have been available, this study is the first to extend such an accurate timescale back 360,000 years.

Kawamura's team found that changes in northern high-latitude summer sunshine preceded the dramatic global warming that ended the last four ice ages. The distribution of sunlight on the planet, which has been precisely estimated, is affected by changes in the Earth's 'orbital parameters', such as the tilt of the Earth's axis. Until now, various mechanisms that drive ice ages on a 100,000 year cycle have been proposed, but the timing of events remained unclear. The results will help climate modellers to better understand the relationship between these factors in simulating global warming scenarios.