A World of Searing Heat and Melted Ice Caps: Climate Model of Early Eocene is 'Scary Finding' for Earth's Future

Scientists have discovered how a spike in carbon dioxide over 50 million years ago may have caused global temperatures to soar to their highest levels in 66 million years—something they have dubbed a "scary finding" in relation to climate change today.

The climate model of the Early Eocene—which took place between 48 to 54 million years ago—has provided researchers with the most detailed picture yet of how temperatures rose to 14 degrees Celsius above what they are today.

"We were surprised that the climate sensitivity increased as much as it did with increasing carbon dioxide levels," Jiang Zhu, an environmental research fellow at the University of Michigan, said in a statement. "It is a scary finding because it indicates that the temperature response to an increase in carbon dioxide in the future might be larger than the response to the same increase in CO2 now. This is not good news for us."

The Early Eocene included the Paleocene-Eocene Thermal Maximum (PETM). During this time, carbon dioxide levels rose significantly and global temperatures soared.

"Geological evidence shows that during the Early Eocene, Earth's surface was at least 14 degrees Celsius warmer on average than right now and that the difference between the equator and polar temperatures was much smaller," Zhu told Newsweek. "The poles were ice free. There were palm trees near the North Pole."

At this time, CO2 levels were around 1,000 parts per million by volume (ppmv). This is over double what they are today. In May, a CO2 level of 414 ppmv was recorded by the Mauna Loa Atmospheric Baseline Observatory at the National Oceanic and Atmospheric Administration (NOAA)—the highest concentration ever seen over 61 years' worth of observations. It is thought atmospheric CO2 will surpass 1,000 ppmv by the end of the century if nothing is done to limit its release.

The Early Eocene is considered a reasonably good analogy for modern climate change. What caused the spike in CO2 during this period is not known, though scientists believe there could have been an increase in volcanic activity.

Previously, climate models were not able to simulate the extreme warming of the PETM because of their limited sensitivity—normally up to around 4.7 degrees Celsius, Zhu and colleagues note in a study published in Science Advances.

The team built on a well known climate model—the Community Earth System Model version 1.2 (CESM1.2)—so that it simulated cloud processes. Decreases in cloud cover allows more solar radiation to reach Earth, increasing global warming. "Temperature increases can then further reduce cloud cover and opacity, forming a positive feedback loop," Zhu explained.

Their model showed how clouds played a huge role in global temperatures. It also found the climate became increasingly sensitive to CO2 as temperatures increased. The rate of warming increased dramatically as CO2 levels rose.

stock global warming
Stock photo representing drought brought on through climate change. Researchers have simulated the climate of a global warming period where temperatures were 14 degrees hotter than they are today. iStock

While Earth is still some way off the CO2 levels seen during the Early Eocene, it shows how the planet might react to the greenhouse gas being pumped into the atmosphere in the future.

Zhu said there are limitations to the work. "In terms of climate forcing from CO2, there is a similarity between the Early Eocene and future climate, but Earth's past climate like the Early Eocene is not a perfect analog for future climate," he said.

"Simulation of cloud processes has been found to vary among different climate models. It is possible that relevant cloud processes will be model dependent."

Dan Lunt, Professor of Climate Science at the U.K.'s University of Bristol, who was not involved in the research, said the study was "one of the most important papers" relating to ancient climate models of the last 10 years.

"For the first time, it shows that a state-of-the-art climate model can simulate a climate of a 'greenhouse' world—in this case the Early Eocene, about 50 million years ago—that is in good agreement with geological data," Lunt told Newsweek.

"Another crucial aspect is that this work gives us substantial additional confidence in the future climate predictions from this and similar climate models. The world of the Early Eocene is not dissimilar from the future world that we may expect under continued greenhouse gas emissions. The modeling and geological data from this time gives us a stark indicator of the sort of world that we may enter if these emissions continue—a world of searing heat and melted ice caps."

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From September 15-23, Newsweek is one of several outlets committed to emphasizing climate stories. The goal is to maximize coverage of the climate crisis and its impacts in the lead up to the United Nations Climate Summit on September 23.

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This story is part of a Covering Climate Now project from the Columbia Journalism Review.

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