Washington: A researcher has said that he has found proof suggesting that no ice sheet formed during the late Cretaceous Period - more than 90 million years ago - when the climate was much warmer than today.
Ken MacLeod , a professor of geological sciences at University of Missouri, said that currently, carbon dioxide levels are just above 400 parts per million (ppm), up approximately 120 ppm in the last 150 years and rising about 2 ppm each year.
He said that during the Late Cretaceous Period, when carbon dioxide levels were around 1,000 ppm, they found there were no continental ice sheets on earth.
MacLeod said that if carbon dioxide levels continue to rise, the earth will be ice-free once the climate comes into balance with the higher levels.
In his study, MacLeod analyzed the fossilized shells of 90 million-year-old planktic and benthic foraminifera, single-celled organisms about the size of a grain of salt.
He said that they know that the carbon dioxide (CO2) levels are rising currently and are at the highest they have been in millions of years.
MacLeod asserted that they have records of how conditions have changed as CO2 levels have risen from 280 to 400 ppm, but he believes that it also is important to know what could happen when those levels reach 600 to 1000 ppm.
He added that at the rate that carbon dioxide levels are rising, we will reach 600 ppm around the end of this century.
The study has been published in journal Geology.