Scientists Project Precisely How Cold the Last Ice Age Was

Researchers used models and data from fossilized plankton to determine the global average temperature at the time

A global map. Dark blue, indicating the greatest change in surface air temperature from 20,000 years ago to now, is concentrated around the poles; lighter blue, indicated less change, closer to the Equator
This global map indicates the temperature differences between now and preindustrial times, where dark blue translates to cooler temperatures. Jessica Tierney, via University of Arizona

About 20,000 years ago, miles of icy glaciers stretched across parts of Europe, Asia, South America and North America, while woolly mammoths, mastodons and saber-toothed cats roamed the land.

Scientists call this period, the point during the Ice Age at which the glaciers covered their largest extent, the Last Glacial Maximum. “We have a lot of data about this time period because it has been studied for so long,” says Jessica Tierney, climate scientist at the University of Arizona, in a statement. “But one question science has long wanted answers to is simple: How cold was the ice age?”

Now, in a study published in Nature this week, lead author Tierney and her team have successfully projected the average global temperature during the Last Glacial Maximum. Based on their models, the researchers found that the global average temperature from 19,000 to 23,000 years ago was about 46 degrees Fahrenheit. That’s about 11 degrees Fahrenheit (6 degrees Celsius) colder than the global average temperature of the 20th century, per a University of Michigan statement.

“In your own personal experience that might not sound like a big difference, but, in fact, it’s a huge change,” Tierney says in the statement.

“Six degrees [Celsius] of global average cooling is enormous. The world would have looked much different during the last glacial maximum,” adds co-author Chris Poulsen, an environmental scientist at the University of Michigan.

As Brooks Hays reports for United Press International, the team analyzed the preserved fats of fossilized marine plankton to map a range of sea-surface temperatures during the last Ice Age, and then fed that data into their models to project the ancient forecast.

Poulsen and postdoctoral fellow Jiang Zhu, both with the University of Michigan, were in charge of creating the model simulations of the LGM weather patterns.

As Will Dunham reports for Reuters, the researchers note that cooling during this period occurred unevenly across the planet. In general, polar regions at higher latitudes cooled much more than tropical regions.

Tierney, Poulsen and Zhu note in statements that their research has important implications for our predictions about human-driven climate change on the planet. In particular, their data can help scientists understand climate sensitivity, or “how much the global temperature shifts in response to atmospheric carbon,” per the University of Michigan statement.

“Past climates are the only information we have about what really happens when the Earth cools or warms to a large degree. So by studying them, we can better constrain what to expect in the future,” Tierney tells Reuters.

“Without having an accurate estimate of the LGM temperature, we couldn’t be confident in how temperature responded to changes in atmospheric carbon,” adds Zhu in the statement. “Our results provide that confidence.”

Jack Williams, a geologist at the Center for Climatic Research at the University of Wisconsin-Madison, wrote on Twitter that the study represents “[a] huge contribution by paleoclimatology to the climate-sensitivity conversation.”

In the future, the team hopes to use this same method to reconstruct periods of warming from Earth’s geological history.

“If we can reconstruct past warm climates, then we can start to answer important questions about how the Earth reacts to really high carbon dioxide levels, and improve our understanding of what future climate change might hold,” says Tierney in the University of Michigan statement.

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