Anthropogenic effects revealed in aged ice cores
25 November 2005
Levels of CO2 in the atmosphere are the highest they have been for 650 000 years, ice core data suggest. The findings add to evidence that recent human activity is affecting the Earth's climate.
Ice cores excavated from two deep drillings in Antarctica provided scientists at the European project for ice coring in Antarctica (EPICA) with a climate record going back 650 000 years, 120 000 years earlier than previous data.
Thomas Stocker at the University of Bern, Switzerland led the team who reconstructed records of CO2, methane, and nitrous oxide from air bubbles trapped in the ice. The data cover four more glacial periods than earlier data, and support theories that global greenhouse gas (GHG) levels are linked to the Earth's temperature.
As glacial and interglacial periods came and went between 390 000 and 650 000 years ago, the relationship between temperature and CO2 levels stayed constant. The warmer the climate, the higher the GHG level. The lower the temperature, the lower the GHG level.
'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,' said team leader Stocker.
Regine Röthlisberger at the British Antarctic Survey, and an EPICA scientist, said the latest ice core data will ultimately help understand global climate processes. 'What we know from this extended record is that the current concentrations of CO2 at 380 ppm have never been seen in the recent past,' she said.
The results will be used by the Intergovernmental panel on climate change, the scientific body that informs politicians and policy makers on climate change and its potential impacts. Katharine Sanderson
U Siegenthaler et al, Science, 2005, 310, 1313
R Spahni et al, Science, 2005, 310, 1317