Ice Sheet Didn't Exist in Late Cretaceous Period: Climate Change Models Impacted

About 90 million years ago, a continental ice sheet first formed during the Last Cretaceous Period--or so scientists believed. Now, it turns out that this might not be the case. One researcher has discovered evidence that suggests no ice formed during this period, which could change climate models that focus on melting ice.

As the climate continues to heat up, ice sheets are melting. As they do, sea levels threaten to rise, which could swamp coastal cities. Learning about how conditions affected this ice sheet in the past could potentially help scientists develop better models to predict melting.

In order to better understand the past climate, the researchers analyzed the fossilized shells of 90-million-year-old planktic and benthic foraminifera. These single-celled organisms are about the size of a grain of salt and can give scientists information about past climatic conditions. More specifically, the researchers measured the ratios of different isotopes of oxygen and carbon in these fossils. Surprisingly, the fossils showed no evidence of cooling or changes in local water chemistry, which would be expected if a glacial event had occurred during this time period.

"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, the researcher who conducted the study, in a news release. "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."

The latest findings, in fact, show that increased CO2 levels may mean higher temperatures than were once predicted. Previously, many scientists believed that doubling CO2 levels would cause earth's temperature to increase as much as 6 degrees Fahrenheit. Yet the temperatures that existed 90 million years ago are more consistent with predictions that doubling CO2 levels will cause the Earth's temperature to rise about 11 degrees Fahrenheit.

"While studying the past can help us predict the future, other challenges with modern warming still exist," said MacLeod in a news release. "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."

The findings are published in the journal Geology.