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Oct. 10, 2013 Volume 35, No. 8

Contrary to science orthodoxy, Late Cretaceous probably ice-free, MU researcher says

For years, scientists believed that a continental ice sheet formed during the Late Cretaceous period about 90 million years ago when the climate was much warmer than today. 

But a University of Missouri researcher has found evidence suggesting that no ice sheet formed at this time. This finding could help environmentalists and scientists predict what the earth’s climate will be as carbon dioxide levels continue to rise.

“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,” said Ken MacLeod, an MU professor of geological sciences. “In our study, we found that during the Late Cretaceous period, when carbon dioxide levels were around 1,000 ppm, there were no continental ice sheets on earth. So if carbon dioxide levels continue to rise, the earth will be ice-free once the climate comes into balance with the higher levels.”

Many scientists say that an ice-free Earth would flood many inhabited coasts, including the American cities of Miami, New York and New Orleans.

MacLeod postulates that, at the rate carbon dioxide is increasing today, the world will be at 600 ppm by the end of this century. “At that level of [carbon dioxide], will ice sheets on Greenland and Antarctica be stable?” MacLeod asked. “If not, how will their melting affect the planet?”

In his study, published in the October issue of the journal Geology, MacLeod analyzed the fossilized shells of Late Cretaceous planktic and benthic foraminifera, single-celled organisms about the size of a grain of salt, discovered in Tanzania. Measuring the ratios of different isotopes of oxygen and carbon in the fossils gives scientists information about past temperatures and other environmental conditions. 

The fossils’ isotopes showed no evidence that there was cooling or changes in local water chemistry during the organisms’ lifespan, MacLeod said. If there were a glacial event 90 million years ago, the isotopes would show that, he said.

“We know that the carbon dioxide levels are rising currently and are at the highest they have been in millions of years,” MacLeod said. “We have records of how conditions changed as [carbon dioxide] levels rose from 280 to 400 ppm, but I believe it also is important to know what could happen when those levels reach 600 to 1000 ppm.” 

Previously, many scientists thought that doubling carbon dioxide levels would cause Earth’s temperature to increase up to 6 degrees Fahrenheit. However, the temperatures MacLeod believes existed in Tanzania 90 million years ago are more consistent with predictions that a doubling of carbon dioxide levels could cause the earth’s temperature to rise an average of 11 degrees Fahrenheit.

“While studying the past can help us predict the future, other challenges with modern warming still exist,” MacLeod said. “We’re seeing the same size changes [today], but they are happening over a couple of hundred years, maybe 10,000 times faster. 

— Jerett Rion