New research suggests that cooling in the Northern Hemisphere may have triggered far-reaching ocean changes that helped drive Earth’s past ice ages.
Growing ice sheets in the Northern Hemisphere may have helped push Earth into past ice ages by triggering changes in ocean circulation thousands of miles away, near Antarctica. New research from the University of St Andrews identifies a possible mechanism connecting these distant regions, helping explain how the planet naturally reduced atmospheric carbon dioxide (CO2) as ice ages developed.
Scientists have long known that the Southern Ocean plays a central role in regulating atmospheric CO2. Changes in its circulation and sea ice can increase the amount of carbon stored in the deep ocean, contributing to the cooling associated with ice ages. But researchers have struggled to explain how expanding northern ice sheets could influence waters so far south.
How Northern Ice Sheets Could Transform the Southern Ocean
The growth of massive Northern Hemisphere ice sheets begins with changes in Earth’s orbit that alter how solar energy is distributed across the planet. According to the new study, published in the Journal of Climate, these expanding ice sheets may set off a much larger chain of events by cooling nearby North Atlantic waters.
As those colder waters move through the global ocean circulation system, they can eventually reach the Southern Ocean. If the northern cooling is strong enough, it could alter circulation around Antarctica and promote conditions that allow more CO2 to remain stored in the ocean rather than the atmosphere.
This proposed connection provides a physical explanation for how ice sheet growth in one hemisphere could help amplify cooling across the planet.
Ocean Simulations Reveal a Powerful Cooling Effect
To test the hypothesis, researchers used computer simulations that cooled only the ocean’s northernmost latitudes (mimicking the effect of a large ice sheet). They then examined whether the temperature changes could travel south and alter Southern Ocean conditions in ways that reduce atmospheric CO2.
The results showed that cooling northern waters alone produced a substantial response. The simulated reduction in atmospheric CO2 reached 74% of the reduction produced when the researchers cooled the entire planet.
The experiments support the proposed connection between Northern Hemisphere ice sheets and Southern Ocean carbon storage. However, they demonstrate that the mechanism is physically plausible in a model, rather than establishing exactly how much it contributed to individual ice ages in Earth’s past.
Rethinking What Drives Earth’s Ice Ages
Lead author Dr. Madison Shankle, from the University of St Andrews’ School of Earth and Environmental Science, explained:
“Essentially, we’ve produced evidence of a plausible mechanism connecting these two far-flung puzzles pieces – Northern Hemisphere ice sheets and Southern Hemisphere ocean circulation changes leading to CO2 drawdown – which has been a tricky thing to explain in our theory of Earth’s past ice ages. Our study takes the step of actually demonstrating them working in model simulations, which is a big step forward for this field.”
Ice age research has traditionally emphasized processes occurring around Antarctica, where ocean circulation strongly influences the exchange of carbon between the atmosphere and deep ocean. The new findings suggest that temperature changes in distant northern waters may also be an important part of that system.
Past ice ages provide natural examples of how carbon moves between Earth’s atmosphere and oceans over long periods. Understanding these processes can help scientists improve climate models and investigate how the global carbon cycle responds to changes in atmospheric CO2, including the additional carbon dioxide released by human activities.
Reference: “Isolated Northern Hemisphere Cooling in an Idealized Model Promotes Ocean Carbon Storage and Glacial-like Ocean Features” by Madison G. Shankle, Graeme A. MacGilchrist, Andrea Burke, Alice Marzocchi, Malte F. Jansen and James W. B. Rae, 22 October 2026, Journal of Climate.
DOI: 10.1175/JCLI-D-25-0355.1
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16 Comments
It makes sense to me, since climate scientist have long said that outgassing of CO2 from the Southern Ocean follows after warming from orbital forcing of Milankovitch cycles, that begin the warming when glacial periods end.
Agreed.
Heat capacity of the atmosphere is equivalent to 2.4 meter depth of water. The mean sphere depth of water on Earth is approximately 2400 meters. Long term climate model without sufficient representation the ocean is a joke, like running a cooperation by the vote of 0.1% minority share holder.
Looks like those scientists in the 1970’s may be correct about the sudden change flipping from global warming to a massive ice age event starting. It’s coming…UFO’s and beings not from earth are more likely with all the Globes and Triangles in the sky now.
and if any country had that tech they would be ruling the world right now.
First of all, there was never anything within a light year of consensus in the 1970s, about a coming global cooling. There were 6 times as many peer reviewed studies on AGW caused by increased CO2 from burning fossil fuels. A handful of scientists were studying what would happen if we increased the amount of sulfur dioxide aerosols to 4 times as much in the atmosphere. – a cooling effect. Within about a year they all changed their minds, realizing the AGW was the real threat. And pollution controls after that soon removed much of our SO2 emissions, which have an atmospheric resident time of 2 or 3 years. CO2 Centuries. Methane about 12 years.
44 published papers on AGW
7 papers on potential cooling from SO2 aerosols.
Each IPCC report is based on about 10,000 peer reviewed studies.
The coming ice age idea was hyped by popular magazines, not scientists.
Nope. There was never anywhere near a consensus on global cooling in the 1970s.
There were 6 Times as Many peer reviewed studies on AGW from our CO2 emissions, about 70% of which is from burning fossil fuels.
44 peer reviewed studies on AGW, 6 studies on cooling,
A handful of scientists were studying what would happen if we quadrupled the amount of atmospheric sulfur dioxide aerosols in the atmosphere, another product of burning fossil fuels.
Within a year or two they all realized that AGW was the real threat.
SO2 aerosols have atmospheric resident times of 2-3 years.
CO2 resident time is measured in centuries, methane about 12 years.
And we never came close to that much increase of SO2. Pollution controls on smokestacks and vehicles greatly reduced those emissions. But they remove zero CO2.
Popular magazines like Time, Newsweek hyped the “coming ice age” nonsense, not scientists.
Theres been at least 7 snowball Earths, an untold Ice ages, over the last million years, an none were the result of a Milancovich event…
There’s only “ONE WAY” to create a Iceage an beyond, if you can bring the AMOC..to a HALT.. then in a pretty short time, you will have a
FULL BLOWN ICEAGE on your hands…..it is naturally, irreversible, at this point.
“…, an [sic] none were the result of a Milancovich [sic] event…”
That is a bold assertion. Do you have a citation to support it?
FALSE
It would cause colder temperatures in Northwest Europe, but would not create an ice age.
The world is now warming 10 Times as fast as the warming that ended glacial periods over the last 1 billion years.
That’s because we are increasing CO2 FAR FASTER than has ever happened in the last 800,000 years. Until we stop burning fossil fuels the warming will not stop.
——————
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 CO2 increase above was 90ppm taking 15,000 years.
WE have done that in about the last 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 146ppm in the last 144 years
———
Correction to my last comment. It should have said warming 10 times faster than warming that ended glacial periods over last 1 million years, not 1 billion.
On the other hand, we are likely increasing CO2 about 10 times as fast as the increase that caused the PETM 56 million years go, with its partial mass extinction. Paleocene Eocene Thermal Maximum.
——————
See here.
Paleontologists reconstruct forests of 56 million years ago with chilling parallels for our warming planet
“Human-caused climate change is now pumping CO2 into the atmosphere at a rate an order of magnitude faster (10 TIMES) than during the ancient event.”
phys. dot org 2026 08
The problem with your claim is that measurements of human emissions are based on highly-motivated tax records, whereas, the PETM estimates are based on proxies with low correlations. The proxies are further confounded by the fact that time acts like a low-pass filter, suppressing and widening the peaks, thus decreasing the slopes of the rates of change.
Theres been at least 7 snowball Earths, an untold Ice ages, over the last million years, an none were the result of a Milancovich event…
There’s only “ONE WAY” to create a Iceage an beyond, if you can bring the AMOC..to a HALT.. then in a pretty short time, you will have a
FULL BLOWN ICEAGE on your hands…..it is naturally, irreversible, at this point.
Considering that AMOC is an acronym for Atlantic Meridional Overturning Current, and the Atlantic Ocean didn’t exist during the Snowball Earth events, this would appear to be an impossible cause.
Yes, the whole article seems to be premised on the assumption that plate tectonics isn’t present and the ancient world had essentially the same geography, winds, and ocean currents as today.
FALSE. There have been zero snowball earth conditions in the last 1 million years, but about a half dozen glacial periods followed by interglacial periods, like the Holocene humans have lived in during the last 11,000 years or so.
Over the last 1 million years Milankovitch cycles were the trigger that started and ended glacial periods. Climate scientists know that the orbital forcing trigger is just that a trigger, and can’t warm the planet on its own, enough to end an glacial period.
AGW deniers often claim that Earth is still coming out of the last ice age (glacial period).
That orbital forcing stopped about 9,000-8,000 years ago, at the Holocene Thermal Optimum.
Then after about 2,000 years of global temperature plateau, a slow gradual cooling began about 6,000 years ago, and continued up to the industrial revolution.
The world has now warmed by about twice as much in 146 years, as it cooled over those 6,000 years.
Guess what is a major player in ending glacial periods? (ice ages in popular speech)
CARBON DIOXIDE
peer reviewed sources:
Martin et al. 2005;
Toggweiler et al. 2006;
Schmittner and Galbraith 2008;
Skinner et al. 2010;
Shakun et al 2012
According to the peer reviewed research by Shakun et al., 93% of the global warming happened AFTER the CO2 increase, when the last glacial period ended.
Milankovitch cycles are not strong enough as radiative forcing to melt ice sheets and warm the world to interglacial conditions on their own. Feedbacks that kick in after the initial warming are what do much if not most of the warming.
CO2 was a major player as a feedback. The warming from CO2 causes other warming feedbacks to kick in, including emissions of more CO2 from oceans, emissions of methane, emissions of water vapor (a greenhouse gas), loss of albedo (reflectivity) as ice melts, etc.
Science deniers have twisted that into a lie, claiming CO2 increase always follows warming.
CO2 will have its greenhouse effect as a feedback or as a forcing as it is now.
Now humans are Directly pumping CO2 into the atmosphere at the rate of about 38 Billion tons a year. So CO2 is acting as a climate forcing, not a feedback. That CO2 warms the atmosphere has been known since 1856. There is no question about that.
The last snowball Earth was over 600 million years ago.
The Sun would have been about 6% weaker than now. It’s output has strengthened by about 1% per 100 million years over the last 1 billion years.
That means it would have required approximately 3,000ppm CO2 just to prevent snowball Earth. So when deniers say “climate has changed for 4.3 billion years” they haven’t the slightest clue about climate science or the history of Earth.
“According to the peer reviewed research by Shakun et al., 93% of the global warming happened AFTER the CO2 increase, when the last glacial period ended.”
That isn’t too surprising because snow and ice has higher reflectivity than vegetation and bare rock. NASA has documented “greening” or increased vegetation, which provides increased cycling of CO2 as the temperature increases. The vegetation detritus also provides food for microbial life to decompose and produce more CO2. Simultaneously, warmth will increase the rate of respiration of CO2 from boreal trees.
CO2 plays a role in the complex, interrelated feedback loops, but probably isn’t the control knob for temperature. Biology clearly drives the seasonal changes, and is therefore probably responsible for the annual increase in CO2.