Late Cretaceous Period was likely ice-free

September 24, 2013, University of Missouri-Columbia
In the study, MacLeod examined fossils of organisms that lived 90 million years ago. This photo is an image from a Scanning electron microscope of a planktic (left) and benthic (right) foraminifera from Tanzania. Both shells are less than 0.5 millimeters across. Credit: University of Missouri

For years, scientists have thought that a continental ice sheet formed during the Late Cretaceous Period more than 90 million years ago when the climate was much warmer than it is today. Now, 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, a professor of at MU. "In our study, we found that during the Late Cretaceous Period, when carbon dioxide levels were around 1,000 ppm, there were no 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."

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. Measuring the ratios of different isotopes of oxygen and carbon in the fossils gives scientists information about past temperatures and other . The fossils, which were found in Tanzania, showed no evidence of cooling or changes in local that would have been expected if a glacial event had occurred during that time period.

"We know that the carbon dioxide (CO2) levels are rising currently and are at the highest they have been in millions of years. We have records of how conditions have changed as CO2 levels have risen 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," MacLeod said. "At the rate that carbon dioxide levels are rising, we will reach 600 ppm around the end of this century. At that level of CO2, will ice sheets on Greenland and Antarctica be stable? If not, how will their melting affect the planet?"

Previously, many scientists have thought that doubling CO2 levels would cause earth's temperature to increase as much as 3 degrees Celsius, or approximately 6 degrees Fahrenheit. However, the temperatures MacLeod believes existed in Tanzania 90 million years ago are more consistent with predictions that a doubling of CO2 levels would cause the earth's temperature could rise an average of 6 degrees Celsius, or approximately 11 degrees Fahrenheit.

"While studying the past can help us predict the future, other challenges with modern warming still exist," MacLeod said. "The Late Cretaceous climate was very warm, but the earth adjusted as changes occurred over millions of years. We're seeing the same size changes, but they are happening over a couple of hundred years, maybe 10,000 times faster. How that affects the equation is a big and difficult question."

MacLeod's study was published in the October issue of the journal Geology.

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2.3 / 5 (15) Sep 24, 2013
There were other factors to consider at that time too. There were no great mountain chains to effect the atmospheric heat transfer between the tropics and the poles. The ocean circulation would have been rather different with most of the continents still packed together on one side of the planet and a "world ocean" covering the rest. The increased volcanism of that era associated with the wide spread formation of rift valleys to name just that ones that occur to me. Also, it may be a bit difficult to form ice sheets where none exist to help initiate a positive feedback through increased albedo.

So, do not be too anxious to single out CO2 levels in probing past climate changes, for even the wise cannot see all factors.
1.5 / 5 (15) Sep 25, 2013
if the world lost all of its ice before, than it can handle losing ALL of its ice again, who is to say man kind will not benefit from all the ice melting.

its possible the existing deserts expand rendering more land uninhabitalbe. but this is will almost certainly be offset by antarctica and the northern canada/greenland/russia polar arctic being rendered habitable.

of course global warming alarmists are worried that such drastic changes will happen overnight displacing billions. in fact, multiple wars and famines occuring in the ordinary course of civlization will cause living patterns changes far more quickly and immidiately than the rapid and major changes in global climate occur which take thousands of years. in the meanwhile, entirely new areas of coastline, such as northern russia and the hudson bay might open up for cities and ports. i for one would summer in antartica and summer at the pole---living in perpetual sunlight for most of my life.
1.6 / 5 (13) Sep 25, 2013
1000ppm is being VERY conservative. The average I am finding is between 1600 and 2000ppm depending on sources and what methodologies being used. I have yet to find a source stating 1000ppm other than this article here.

Even then, 2ppm a year from 400, to get to 1000 would require 300 years at our current rate.

We don't have 300 years worth of fossil fuels so...

Hell we don't even have 100 years probably, maybe just about.

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