Atmospheric carbon dioxide (CO2) levels have reached their highest in more than 2.1 million years, according to a new study of the earth’s heating and cooling cycles.

Researchers from Columbia University’s Lamont-Doherty Earth Observatory in New York confirmed that periods of high CO2 concentrations coincided with noticeable temperature rises.

Publishing their findings in the journal Science, the scientists found that today’s peak CO2 level is 38 percent above an average taken over the past 2.1 million years.

Lead researcher Barbel Honisch and her team were able to reconstruct CO2 data by looking at the shells of single-celled plankton buried under the Atlantic Ocean.

This allowed them to look much further back than studies of polar ice cores, which are only 800,000 years old.

“Previous studies indicated that CO2 did not change much over the past 20 million years, but the resolution wasn’t high enough to be definitive,” said Professor Honisch.

“This study tells us that CO2 was not the main trigger, though our data continues to suggest that greenhouse gases and global climate are intimately linked.”