Led by ocean plankton fossils and climate models, scientists have calculated how cold the earth became in the depths of the last ice age, when immense ice sheets covered large parts of North America, South America, Europe and Asia.
The average world temperature in the period known as the last glacier maximum from about 23,000 to 19,000 years ago was about 46 degrees Fahrenheit (7.8 degrees Celsius), about 13 degrees Fahrenheit (7 Celsius) colder than 2019, the researchers said Wednesday.
Certain regions were much cooler than the global average, they found. The polar regions cool much more than the tropics, with the Arctic region 25 degrees Fahrenheit (14 degrees Celsius) colder than the global average.
The researchers made their calculations using chemical measurements on small fossils of zooplankton and the stored structures of fats from other types of plankton that change in response to water temperature – what they called a “temperature proxy”.
This information was then plotted in simulations of climate models to calculate average global temperatures.
“Climates in the past are the only information we have about what really happens when the earth cools or warms to a great extent. That by studying them, we can better limit what we can expect in the future,” said paleoclimatologist Jessica Tierney, University of Arizona, lead author of the study published in the journal Nature.
During the ice age, which lasted from about 115,000 to 11,000 years ago, large mammals adapted well to a cold climate as the mammoths, mastodons, woolly rhinos and saber cats roamed the landscape.
People entered North America for the first time during the ice age, by crossing a land bridge that once connected Siberia to Alaska with sea levels much lower than they are today.
It is believed that human hunting contributed to the extinction of many species at the end of the Ice Age.
“What’s interesting is that Alaska was not completely covered in ice,” Tierney said. “There was an ice-free corridor that people traveled across Bering Street, in Alaska. Central Alaska was actually not that much colder than today, so for people of the ice age, it could have been a relatively nice place to live. “
