Antarctic ice sheets melted rapidly 20 million years ago due to orbital changes. Researchers warn modern emissions could trigger similar instability, urging climate action.
Geoscientists led by the University of Leicester and the University of Southampton have discovered periods of sudden melting in the Antarctic ice sheet in a new climate record from over 20 million years ago. The research, recently published in Nature Communications, reveals how sensitive our planet’s early ice ages were to the effect of the Earth’s eccentric orbit around the Sun, indicating that the Antarctic ice sheet may be less stable than previously thought. Additionally, the study offers insights into how the Antarctic may behave in a world without the Greenland Ice Sheet, which will melt if emissions continue unabated.
Antarctic Ice Sheet Through Time
Records show that the Antarctic ice sheet has varied in size throughout history. These variations in size occur regularly, just like a heartbeat. Existing records from different places in the ocean show different ‘rhythms’ in the heartbeat of early Antarctic ice ages. This should not be possible because the imprint of the waxing and waning of the Antarctic ice sheet on the climate record should be identical everywhere in the ocean, just as it should not be possible that your leg has a different pulse rate than your arm.
Eccentric Orbits and Climate Rhythms
These heartbeat rhythms are caused by the shape of Earth’s orbit around the Sun over the course of hundreds of thousands to millions of years. On a more eccentric orbit, the Earth’s distance from the Sun will vary more throughout the year, exposing it to more heat when it is close in and less when it is further away. The increasing heat changes Earth’s climate system, sometimes causing the ice sheet to melt rapidly. When the Earth’s orbit is more circular, the ice sheet is more stable, and less melting occurs.
Geological Clues to Past Climates
This new study, funded by UK Research and Innovation/Natural Environment Research Council and the German Science Foundation (DFG) examines the period between 28 and 20 million years ago, when Earth was warmer than today and only the Antarctic ice sheets existed. Using data from geological cores recovered by an expedition of the Integrated Ocean Drilling Program (IODP), the research presents a new benchmark climate record to compare existing records to help scientists improve the accuracy of their climate models reconstructing past climate change. These insights into the past help them understand the impact of the melting of the Antarctic Ice Sheet in the future.
A Warning from the Past
Lead author Dr Tim van Peer, from the University of Leicester School of Geography, Geology and the Environment, said: “From our research, we can see that the Antarctic ice sheet is more unstable than previously thought. We demonstrate how sensitive the geologically early Antarctic ice sheet was to changes in Earth’s orbit and axis.
“Past climate changes rapidly ended some of the early Antarctic ice ages and caused large amounts of melt. ‘Rapidly’ is on geological time scales, not as rapid as we can expect to happen during modern climate change.
“We cannot assume that the modern-day Antarctic ice sheet is stable. If climate emissions continue unabated, we are on course to melt a large amount of the Antarctic ice sheet. We need to mitigate climate change by reducing our emissions. This is the only way to not cross tipping points in the stability of the Antarctic ice sheet.”
Probing Deep-Sea Evidence
The research analyzed samples from geological cores obtained from the northwest Atlantic Ocean as part of an IODP expedition in 2012. Microorganisms from these cores record the chemistry of the ocean in the form of oxygen isotopes in their shells. By measuring the oxygen isotope ratio, the scientists can work out if the ice sheet has grown or shrunk, and establish a timeline from the depth of that sample in the cores.
Professor Paul Wilson, Principal Investigator on the project at the University of Southampton, said: “It may be a surprising thing to learn that we take the pulse of the Antarctic ice sheet by doing some simple chemistry on pinhead-sized fossil shells from the deep sea floor on the other side of the world. But the really beautiful thing is that we can do it back through the geological record over tens of millions of years. Earth science is about time travel into the past and we are always learning lessons to help us understand our future.”
Global Collaboration in Marine Science
IODP is a publicly-funded international marine research program supported by 21 countries, which explores Earth’s history and dynamics recorded in seafloor sediments and rocks, and monitors sub-seafloor environments. Through multiple platforms – a feature unique to IODP – scientists sample the deep biosphere and sub-seafloor ocean, environmental change, processes and effects, and solid Earth cycles and dynamics. This specific research uses samples collected during Expedition 342 and has taken years of work from the combined efforts of a multinational partnership (mainly UK and Germany).
The University of Leicester has been involved in IODP since the 1980s and participated in dozens of expeditions around the world. Over the last year, University of Leicester scientists participated in IODP Expedition 389 ‘Hawai’ian Drowned Reefs’ and Expedition 405 ‘Tracking Tsunamigenic Slip Across the Japan Trench (JTRACK)’.
Reference: “Eccentricity pacing and rapid termination of the early Antarctic ice ages” by Tim E. van Peer, Diederik Liebrand, Victoria E. Taylor, Swaantje Brzelinski, Iris Wolf, André Bornemann, Oliver Friedrich, Steven M. Bohaty, Chuang Xuan, Peter C. Lippert and Paul A. Wilson, 5 December 2024, Nature Communications.
DOI: 10.1038/s41467-024-54186-1
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9 Comments
First, the authors acknowledge that things other than CO2 can and have caused melting a very long time ago when they say, “The research, … reveals how sensitive our planet’s early ice ages were to the effect of the Earth’s eccentric orbit around the Sun, indicating that the Antarctic ice sheet may be less stable than previously thought.”
They also remark, “When the Earth’s orbit is more circular, the ice sheet is more stable, and less melting occurs.” They neglect to mention that the Earth’s orbit is currently eccentric, and the southern hemisphere is closer to the sun in the southern Summer.
Then, they imply those things are no longer applicable and we only have to worry about CO2 when they say, “Additionally, the study offers insights into how the Antarctic may behave in a world without the Greenland Ice Sheet, which will melt if emissions continue unabated.”
Basically, as I have come to expect, a lot of arm waving and little quantitative information.
The Milankovitch orbital cycles they are referring to would now have the planet Cooling, NOT warming. The warming from that orbital forcing ended at the Holocene Thermal Maximum about 9,000 to 8,000 years ago. Then after a plateau in global temperature for a few thousand years, a slight gradual cooling started 7,000-6,000 years ago, and continued up into the present. Just because Earth’s orbit is eccentric now, that doesn’t mean it’s now the closest to the Sun during that eccentricity.
The warming now happening is about 10 times as fast as the warming that ends ice ages (glacial periods).
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“As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years.
In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly TEN TIMES FASTER than the average rate of ice-age-recovery warming.”
NASA Earth Observatory
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That is from 2010. The warming since 1880 is now almost double, the 0.7C warming NASA was referring to.
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Nobody ever said CO2 is the only factor.
And here’s why the focus Should Be on CO2.
“The maximum rate of change in CO2 concentrations from the ice core records is around 100 ppm in 10,000 years, or around 1 ppm per century.
The current rate of change in CO2 concentrations is 1 ppm every 21 weeks.”
NASA Climate Change
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That comes to 247 times faster now.
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Nature caused CO2 increases over the last 450,000 years, from ice core data
80ppm increase — took 50,000 years
110ppm increase — 25,000 years
120ppm increase — 20,000 years
60ppm increase — 20,000 years
90ppm increase — 15,000 years
100ppm increase — 24,800 years
The fastest natural increase above was 90ppm taking 15,000 years.
We have done that in about 65 years.
Humans increased CO2 by 25ppm in the last 10 years
Humans increased CO2 by 45ppm in the last 20 years.
Humans increased CO2 by over 80ppm in the last 60 years
Humans increased CO2 by 100ppm in the last 70 years
Humans increased CO2 by 144ppm in the last 143 years
Funny that you should mention ice cores. The cores from Law Dome (Antarctica) strongly suggest that for the last 800,000 years temperatures have changed before CO2 did.
I’m not willing to accept your numbers at face value because the sinks can’t differentiate between anthropogenic and natural CO2. The best ‘evidence’ for anthro’ contributions comes from isotopic carbon ratios. However, from what I have seen, none of these analyses take into account isotope fractionation that favors 12C When CO2 out-gases from water. Correlation does not establish causation and the fact that sales taxes demonstrate that annual anthro’ emissions (about 4% of total annual CO2 fluxes) are about twice the estimated accumulation in the atmosphere is not compelling. There are good arguments that it is a spurious correlation.
Thank you for the link. I will look at it.
I don’t know if links are allowed here, but you can find this article
Why Milankovitch (Orbital) Cycles Can’t Explain Earth’s Current Warming
climate dot nasa dot gov / blog
The link didn’t take me to the expected discussion of Milankovitch Cycles.
However, I did stumble across a graph of CO2 for the last 800,000 years. It is poor practice to splice or conflate direct instrumental measurements with older proxy data of unspecified correlation. Few, if any, proxy measurements are perfect and there isn’t any way of verifying the measurements. Analytical protocols can introduce errors and it isn’t known how much CO2 may diffuse out of the ice, let alone the unconsolidated firn. More importantly, time acts like a low-pass filter, suppressing transient peaks, the very thing being compared because the snow is compressed, reducing the age resolution, and exposed ice can be ablated by winds causing sublimation. The ice cores are the best we have, but they leave a lot to be desired in recording extreme transient events such as we are currently experiencing.
“The Milankovitch orbital cycles they are referring to would now have the planet Cooling, NOT warming.”
The article is about the analysis of Antarctic sediments from 20-28 MILLION years ago, not a few thousand years ago.
“Just because Earth’s orbit is eccentric now, that doesn’t mean it’s now the closest to the Sun during that eccentricity.”
That is true. Other lines of evidence (astronomical) have established the eccentricity and that the Earth’s orbit is now closest to the sun during the Southern Hemisphere Summer. While the net insolation for Earth may be low, it appears that the eccentricity is only slightly lower than a few centuries ago. However, we do appear to be living in unusual times, having recently come down from a peak in insolation at 65 deg N. The temporal resolution is too low to come to any firm conclusions.
https://en.wikipedia.org/wiki/Milankovitch_cycles
“In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly TEN TIMES FASTER than the average rate of ice-age-recovery warming.”
That is an assertion that is difficult to prove. There have been some researchers that have claimed the the North American glaciers melted in much less than a century.
The discussion is about the sensitivity of Antarctica’s ice-sheet to changing circumstances. Whether those circumstances be changes in to the Earth’s orbit or whatever else, the Antarctic ice sheet is more sensitive to them than expected.
So that old drill-ship is still plodding 7 sea . I trust that the science lab has worked a change in its horrible rock music .
As I quoted, they specifically addressed the eccentricity of Earth’s orbit. Their research does not examine the impact of increasing CO2. They only make an assertion about it without providing any original research to support the assertion. By expanding their concern about the impact of orbital eccentricity to include all “changing circumstances,” you are imposing your personal biases on their research. Their coat-tails are not strong evidence that all “changing circumstances” are equally detectable or contribute equally to instability.
Tell us about your role in the research while on board the ship.