Ice Core Extends Climate Record Back 650,000 Years

Researchers have recovered a nearly two-mile-long cylinder of ice from eastern Antarctica that contains a record of atmospheric concentrations of carbon dioxide (CO2) and methane--two potent and ubiquitous greenhouse gases--spanning the last two glacial periods. Analysis of this core shows that current atmospheric concentrations of CO2--380 parts per million (ppm)--are 27 percent higher than the highest levels found in the last 650,000 years.

The ice core data also shows that CO2 and methane levels have been remarkably stable in Antarctica--varying between 300 ppm and 180 ppm--over that entire period and that shifts in levels of these gases took at least 800 years, compared to the roughly 100 years in which humans have increased atmospheric CO2 levels to their present high. "We have added another piece of information showing that the timescales on which humans have changed the composition of the atmosphere are extremely short compared to the natural time cycles of the climate system," says Thomas Stocker of the University of Bern in Switzerland, who led the research.