Current levels of greenhouse gases in the atmosphere are higher than at any time in the past 650,000 years, say researchers who have finished cataloguing air bubbles trapped for millennia inside Antarctic ice. The record, which extends back over the past eight ice ages, shows that today's concentrations of carbon dioxide and methane far outstrip those in the past.

Atmospheric carbon dioxide levels have risen 200 times faster over the past 50 years than at any other time during this period, says Thomas Stocker of the University of Bern, Switzerland, who led the analysis.

The researchers studied air bubbles preserved in ice drilled from the Antarctic ice sheet as part of the European Project for Ice Coring in Antarctica (EPICA). The ice core represents a logbook of the state of the world's climate (see 'Frozen time') and goes back 210,000 years further than previous records.

After searching ice spanning the period of 390,000-650,000 years before present, Stocker's team has discovered that carbon dioxide levels in the atmosphere did not exceed 290 parts per million during that time. Today, that figure is around 375 parts per million.

The situation is similar for methane: during this period, levels hovered around 600 parts per billion. Today's atmospheric methane concentration is well over 1,700. Stocker and his colleagues report the results in Science