WASHINGTON -- A new study has shown that current CO2 levels are higher than the last 2.1 million years.

The study is the latest to rule out a drop in CO2 as the cause for earth’s ice ages growing longer and more intense some 850,000 years ago.

But it also confirms many researchers’ suspicion that higher carbon dioxide levels coincided with warmer intervals during the study period.

The authors show that peak CO2 levels over the last 2.1 million years averaged only 280 ppm; but today, CO2 is at 385 ppm, or 38% higher.

This finding means that researchers will need to look back further in time for an analog to modern day climate change.

In the study, Barbel Honisch, a geochemist at Lamont-Doherty Earth Observatory, and her colleagues reconstructed CO2 levels by analyzing the shells of single-celled plankton buried under the Atlantic Ocean, off the coast of Africa.

By dating the shells and measuring their ratio of boron isotopes, they were able to estimate how much CO2 was in the air when the plankton were alive.

This method allowed them to see further back than the precision records preserved in cores of polar ice, which go back only 800,000 years.

The planet has undergone cyclic ice ages for millions of years, but about 850,000 years ago, the cycles of ice grew longer and more intense-a shift that some scientists have attributed to falling CO2 levels.

But, the study found that CO2 was flat during this transition and unlikely to have triggered the change.

A global drawdown in CO2 is one theory proposed for the transition.

“The low CO2 levels outlined by the study through the last 2.1 million years make modern day levels, caused by industrialization, seem even more anomalous,” said Richard Alley, a glaciologist at Pennsylvania State University.

“We know from looking at much older climate records that large and rapid increase in C02 in the past, (about 55 million years ago) caused large extinction in bottom-dwelling ocean creatures, and dissolved a lot of shells as the ocean became acidic. We’re heading in that direction now,” he added. (ANI)