The researchers made their calculations using chemical measurements on tiny zooplankton fossils and on the fat-preserved structures of other types of plankton that change in response to water temperature – what they called a “temperature proxy”.
This information was then fed into climate model simulations to calculate average global temperatures.
“Past climates are the only information we have about what really happens when the Earth cools or warms to a large extent. So by studying them, we can better determine what to expect in the future, ”said University of Arizona paleoclimatologist Jessica Tierney, senior author of the research published in the journal Nature.
During the Ice Age, which lasted around 115,000 to 11,000 years ago, large mammals well adapted to a cold climate such as mammoths, mastodons, woolly rhinos and saber-toothed cats roamed the landscape.
Humans first entered North America during the Ice Age, crossing a land bridge that once connected Siberia to Alaska with sea level much lower than today.
It is believed that human hunting contributed to the worldwide mass extinctions of many species at the end of the Ice Age.
“The interesting thing is that Alaska was not completely covered in ice,” Tierney said. “There was an ice-free corridor that allowed humans to cross the Bering Strait, Alaska. Central Alaska was actually not much colder than it is today, so for Ice Age humans this might have been a relatively pleasant place to settle.