By Caroline Catherman, Dec. 30, 2020 –
New research has found a big flaw in one of the most widely accepted theories about earth’s climate, Milutin Milankovitch’s century-old theory of ice ages. This evidence, which echoes past findings, means that some long-term climate predictions could be more inaccurate than scientists realize, the researchers said. But they worry that this vital information won’t become general knowledge for years.
“It takes about a generation of new scientists to remove older ideas and bring newer ideas in,” said Thomas Lowell, professor of geology at the University of Cincinnati, during the recent Comer Climate Conference, an annual national conference held over Zoom this year.
The theory in question proposes that gradual changes in our planet’s movements and position add up over time to vary how much solar radiation reaches Earth. This variation in solar radiation affects whether each hemisphere experiences periods of cooler or warmer summers. Milankovitch predicted that thousands of years of colder summers cause ice ages.
“If you surveyed 100,000 geologists, 99,099 would say that’s correct, in terms of causing ice ages. But it has one big problem,” said Brenda Hall, a professor of glacial & quaternary studies at the University of Maine’s Climate Change Institute.
The theory’s hidden undoing
Milankovitch predicts that ice ages would occur at opposite times in the Northern and Southern Hemispheres. When one hemisphere was having cold summers, and heading towards an ice age, the other would be having warm summers, heading away from an ice age.
But Hall and Lowell’s new research from the Falkland Islands corroborates recent research in New Zealand by suggesting that the two hemispheres experienced the last major ice age, which peaked about 20,000 years ago, at nearly the same time.
These findings, currently undergoing peer review for publication, mean that scientists may not fully understand why the planet goes in and out of ice ages, said Hall.
This, Hall said, is crucial to understanding climate change.
“If we want to have any hope of making climate predictions, we need to know how the different pieces of the system work,” she said.
Hall added that researchers should begin considering other theories. One older theory is the idea that, rather than gradually shifting in and out of ice ages, earth’s climate rapidly changes due to sudden triggers. If true, this would have troubling implications for Earth’s future climate.
“If we can have ice age cycles, these massive changes in climate, because of very small changes … that tells us that a very small change could produce a big reaction. And we’re in the process of initiating one of those changes,” Hall said, referring to human-caused increases in greenhouse gas emissions.
But before many climate researchers will reconsider whether this theory is accurate, they must be convinced that the issue is up for debate.
Scientists are battling to replace a broken theory
Convincing scientists to consider alternative theories is a long process that some people have been attempting since as far back as 1984, when John Mercer published a paper with evidence of simultaneous ice ages.
“I feel like there have been some proposals as to, ‘what else could it be?’” said Meredith Kelly, associate professor of earth science at Dartmouth College. “Until we figure that out, and it’s really well tested, and well-explained, it’s not going to show up in textbooks.”
Lowell said that scientists in older generations are the biggest defenders of Milankovitch because they were taught to regard his theory as fact.
“If you look at the world, and everybody tells you it’s flat for 40 years … and you walk around and you discover that it’s not flat … you’re gonna have problems convincing people who haven’t traveled out of their flat sphere that the earth is round,” Lowell said.
Why Milankovitch’s theory gained acceptance
Several prominent studies have appeared to support Milankovitch’s theory. A 1976 study, for example, found evidence of a correlation between earth’s cycle in and out of ice ages and the so-called Milankovitch cycles. Lowell said these findings were strong enough that many people thought the issue was resolved, even though there was no evidence that this was a cause and effect relationship.
It also took a long time to build evidence against Milankovitch because the Southern Hemisphere wasn’t as well studied as the Northern Hemisphere. When scientists found evidence that the Southern Hemisphere came out of the ice age at the same time as the north, the evidence was initially dismissed as a fluke, said Lowell.
The new generation of scientists is key
“[The Milankovitch Theory] made sense. It wasn’t until you get into the details that you start pulling a thread, and it starts unraveling,” Lowell said. “It’s taken a long time… to get to where we are today.”
Lowell hopes that scientists in the next generation will weave up a new idea with the unraveled Milankovitch thread. For her part, Meredith Kelly has done her best to correct the canonical theory during her 12 years of teaching an intro to geology class, even as she gives her students a textbook that reveres Milankovitch.
“One of the students on the first day asked me if I was going to teach about Milankovitch, and I told her, ‘Yes, but I’m going to tell you that he’s wrong,’” Kelly said with a laugh.
Professors such as Kelly give Lowell hope.
“Science will march on,” he concluded.
Caroline Catherman covers health, environment, and science news at Medill. You can follow her on Twitter at @CECatherman.