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<http://news.bbc.co.uk/2/hi/science/nature/4467420.stm>


        
Last Updated: Thursday, 24 November 2005, 19:40 GMT
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CO2 'highest for 650,000 years'
By Richard Black
Environment Correspondent, BBC News website

Microscope picture of gas bubbles in ice. Image: W. Berner/University of Bern
Gas bubbles trapped in ice store valuable climatic information
Current levels of the greenhouse gases carbon dioxide and methane in the atmosphere are higher now than at any time in 
the last 650,000 years.

That is the conclusion of new European studies looking at ice taken from 3km 
below the surface of Antarctica.

The scientists say their research shows present day warming to be exceptional.

Other research, also published in the journal Science, suggests that sea levels may be rising twice as fast now as in 
previous centuries.

Treasure dome

The evidence on atmospheric concentrations comes from an Antarctic region 
called Dome Concordia (Dome C).

Ice core. Image: J. Schwander/University of Bern
Epica drills have extracted ice from 3km under the Antarctic surface
Over a five year period commencing in 1999, scientists working with the European Project for Ice Coring in Antarctica 
(Epica) have drilled 3,270m into the Dome C ice, which equates to drilling nearly 900,000 years back in time.

Gas bubbles trapped as the ice formed yield important evidence of the mixture of gases present in the atmosphere at that 
time, and of temperature.

"One of the most important things is we can put current levels of carbon dioxide and methane into a long-term context," 
said project leader Thomas Stocker from the University of Bern, Switzerland.

"We find that CO2 is about 30% higher than at any time, and methane 130% higher than at any time; and the rates of 
increase are absolutely exceptional: for CO2, 200 times faster than at any time in the last 650,000 years."

Stable relationship

Last year, the Epica team released its first data. The latest two papers analyse gas composition and temperature dating 
back 650,000 years.

This extends the picture drawn by another Antarctic ice core taken near Lake Vostok which looked 440,000 years into the 
past.

The extra data is crucial because around 420,000 years there appears to have been a significant shift in the Earth's 
long-term climate patterns.

Before and after this date, the planet went through 100,000 year cycles of alternating cold glacial and warm 
interglacial periods.

Antarctic base. Image: A. Lori/ENEA
The base at Dome Concordia
But around the 420,000 year mark, the precise pattern changed, with the contrast between warm and cold conditions 
becoming much more marked.

The Dome C core gives data from six cycles of glaciation and warming; two 
from before this change, four from after.

"We found a very tight relationship between CO2 and temperature even before 
420,000 years," said Professor Stocker.

"The fact that the relationship holds across the transition between climatic regimes is a very strong indication of the 
important role of CO2 in climate regulation."

Epica scientists will now try to extend their analysis further back in time.

Water rise

Another study reported in the same journal claims that for the last 150 years, sea levels have been rising twice as fast 
as in previous centuries.

Using data from tidal gauges and reviewing findings from many previous studies, US researchers have constructed a new 
sea level record covering the last 100 million years.

They calculate the present rate of rise at 2mm per year.

"The main thing that's changed since the 19th Century and the beginning of modern observation has been the widespread 
increase in fossil fuel use and more greenhouse gases," said Kenneth Miller from Rutgers University.

The Intergovernmental Panel on Climate Change, the body which collates scientific evidence for policymakers, concludes 
that sea level rose by 1-2cm during the last century, and will rise by anything up to 88cm by the end of this century.