Current carbon dioxide levels highest in past 2.1 mn years

Present day carbon dioxide levels in the atmosphere have touched the highest mark in the past 2.1 million years which may result in large scale climatic changes from the greenhouse effect, says a study.

The study published in the June 19 edition of the journal Science says the present levels of carbon dioxide are 38 per cent higher than the levels that hovered around 280 parts per million during last 2.1 million years.

Researchers from Columbia University say that the estimation of atmospheric carbon dioxide for the period will give an insight in the cooling and warming cycles of planet earth.

Carbon dioxide is a principal green house gas which traps the warm infrared rays coming from the sun and blocks them from being reflected again into space by the earth's surface.

This helps in maintaining adequate temperature on earth, making it liveable. But its rapid increase emanating from human activities like vehicles, factories etc is increasing the temperature to an extent that large scale climate change is becoming inevitable.

The analysis of carbon dioxide helped scientists learn that a dip in gas levels was the factor for ice ages growing longer and more intense some 8.5 lakh years ago.

"The findings also confirm the suspicion that higher carbon dioxide levels coincided with warmer intervals during the study period," lead author Barbel Honisch, a geo-chemist at Lamont-Doherty Earth Observatory at Columbia University says.

He along with his team reconstructed the levels of the gas by analysing microbes buried in the Atlantic Ocean for lakhs of years. Using modern analytical techniques, the team managed to estimate the levels of carbon dioxide when they would have been alive.

The method helped them estimate levels much beyond the period that could be analysed using the polar ice method where scientists use the gas trapped between the ice to estimate the levels.

"This method helped to see further back than the precision records preserved in cores of polar ice, which go back only eight lakh years," Honisch said. "Our data continues to suggest that greenhouse gases and global climate are intimately linked."

The length of ice age is dependent on earth's orbit and tilt, which determines the amount of sunlight that falls on each hemisphere.

Two million years ago ice ages were following cycle of 41,000 years but about 8.5 lakh years their length expanded to one lakh years. The phenomenon, it was speculated, was the result of drop in gas level but the present study refuted the speculation, researchers say.