NORWICH (Reuters) - Air from the oldest ice core confirms human activity has increased the greenhouse gas carbon dioxide (CO2) in the atmosphere to levels not seen for hundreds of thousands of years, scientists said on Monday.

Bubbles of air in the 800,000-year-old ice, drilled in the Antarctic, show levels of CO2 changing with the climate. But the present levels are out of the previous range.

"It is from air bubbles that we know for sure that carbon dioxide has increased by about 35 percent in the last 200 years," said Dr Eric Wolff of the British Antarctic Survey and the leader of the science team for the 10-nation European Project for Ice Coring in Antarctica.

"Before the last 200 years, which man has been influencing, it was pretty steady," he added.

The natural level of CO2 over most of the past 800,000 years has been 180-300 parts per million by volume (ppmv) of air. But today it is at 380 ppmv.

"The most scary thing is that carbon dioxide today is not just out of the range of what happened in the last 650,000 years but already up 100 percent out of the range," Wolff said at the British Association Festival of Science in Norwich, eastern England.

CO2 was close to 280 ppmv from 1000 AD until 1800 and then it accelerated toward its present concentration. Wolff added that measurements of carbon isotopes showed the extra CO2 coming from a fossil source, due to increased human activity.

The ice core record showed it used to take about 1,000 years for a CO2 increase of 30 ppmv. It has risen by that much in the last 17 years alone.

"We really are in a situation where something is happening that we don't have any analog for in our records. It is an experiment that we don't know the result of," he added.

Professor Peter Smith, of the University of Nottingham in England, said the study showed more needed to be done.

"There is an urgent need to find innovative technologies to reduce the impact we are having on our climate," he told the science conference.

Commentary: