Artist’s AI depiction of New York City in the next Ice Age. (© Creative Valley – stock.adobe.com)
Carbon emissions probably canceled Earth’s next icy climate appointment, expected to occur in 10,000 years
In a nutshell
- Earth naturally cycles between ice ages and warm periods based on three astronomical cycles: precession (Earth’s wobble), obliquity (tilt), and eccentricity (orbit shape).
- Scientists can now predict these cycles with remarkable accuracy, finding that without human influence, Earth would begin cooling toward another ice age in about 10,000 years.
- Human greenhouse gas emissions have disrupted this natural cycle, providing a measurable baseline against which we can quantify our impact on Earth’s climate system.
LONDON — In a world free from human influence, Earth would begin sliding into another ice age roughly 10,000 years from now. This striking prediction comes from research that has finally deciphered the mysterious rhythm governing our planet’s glacial cycles over the past million years.
By analyzing ancient climate records preserved in ocean sediments, researchers from Cardiff University, UC Santa Barbara, Alfred Wegener Institute, and University College London have identified how three specific orbital cycles control the timing of Earth’s ice ages with remarkable precision. Their findings, published in the journal Science, show that these cycles operate like a celestial clock with predictable patterns that have controlled Earth’s climate for hundreds of thousands of years.
“And because we are now living in an interglacial period – called the Holocene – we are also able to provide an initial prediction of when our climate might return to a glacial state,” said Polychronis Tzedakis, a professor at University College London and co-author of the study.
However, this natural climate trajectory has already been fundamentally altered. “Such a transition to a glacial state in 10,000 years’ time is very unlikely to happen because human emissions of carbon dioxide into the atmosphere have already diverted the climate from its natural course, with longer-term impacts into the future,” added co-author Gregor Knorr from the Alfred Wegener Institute.
Cracking the Ice Age Code
Deep within Earth’s geological record lie the fingerprints of dozens of ice ages – long periods when massive ice sheets covered much of North America and northern Europe. Between these frigid epochs were warm periods like today’s, when the ice retreated.
Scientists have long known that Earth’s periodic ice ages follow astronomical patterns first proposed by Serbian mathematician Milutin Milankovitch in the early 20th century. But the exact mechanisms behind these cycles, particularly the dominant 100,000-year pattern that has characterized the last million years of Earth’s climate, remained mysterious until now.
The research team, led by Stephen Barker of Cardiff University, with collaborators including Lorraine Lisiecki from UC Santa Barbara, took an innovative approach to solve this puzzle. Instead of relying on precise dating of climate records—which has limitations—they examined the shape and timing of glacial cycles themselves.
“We found a predictable pattern over the past million years for the timing of when Earth’s climate changes between glacial ‘ice ages’ and mild warm periods like today, called interglacials,” said Lisiecki, a professor in UCSB’s Earth Science Department.
Their findings reveal a predictable system where future climate can be forecast based on orbital mechanics alone—at least in a world without human-caused climate change. Their model accurately predicted all major glacial terminations and warm periods over the past 900,000 years.
“The pattern we found is so reproducible that we were able to make an accurate prediction of when each interglacial period of the past million years or so would occur and how long each would last,” Barker said. “This is important because it confirms the natural climate change cycles we observe on Earth over tens of thousands of years are largely predictable and not random or chaotic.”
The Three Astronomical Forces Behind Ice Ages
The study found that each of three astronomical cycles plays a distinct role in this climate dance:
- Precession — the wobble of Earth’s axis that changes which hemisphere faces the Sun during summer — drives the early stages of deglaciation when ice sheets begin to melt.
- Obliquity — the tilt of Earth’s axis that controls the contrast between seasons — dominates glacial inception, when ice sheets begin to grow again.
- Eccentricity — the shape of Earth’s orbit around the sun — sets the overall timing of the approximately 100,000-year cycles.
“We were amazed to find such a clear imprint of the different orbital parameters on the climate record,” added Barker. “It is quite hard to believe that the pattern has not been seen before.”
Why Geography Controls Climate Response
This astronomical choreography works because of geography. Ice sheets begin forming at high northern latitudes, where obliquity has its strongest influence on summer energy. As they grow and extend southward, they become increasingly vulnerable to precession, which has more impact at lower latitudes.
When ice sheets reach their maximum extent, even slight increases in summer intensity from precession can trigger their collapse—but only during specific orbital alignments.
The researchers discovered that glacial terminations (when ice sheets melt rapidly) occur with the first suitable precession peak that follows a minimum in eccentricity. These suitable peaks must begin while obliquity is increasing, providing a dual warming mechanism that kicks ice sheets into retreat.
The Timing of Ice Ages Decoded
What makes this finding powerful is its ability to predict not just when ice ages end, but how long the warm periods last. When precession and obliquity peak at similar times, deglaciations happen relatively quickly. But when these cycles are out of phase, with precession peaking long before obliquity, deglaciations become prolonged affairs, delaying the arrival of full warm conditions.
This relationship explains why some warm periods, like one about 400,000 years ago, lasted far longer than others. It wasn’t just about the intensity of orbital forcing, but about the relative timing of the astronomical cycles.
The study also resolves a long-standing puzzle in climate science. Direct warming from eccentricity is extremely weak, yet Earth’s climate has followed a roughly 100,000-year cycle for the past million years.
The researchers found that eccentricity matters not because of its direct warming effect, but because it modulates the strength of precession. During periods of low eccentricity, precession’s influence weakens, allowing ice sheets to grow larger without triggering early collapse. Eventually, they reach a critical size and latitude where even modest summer warming can initiate their demise.
Earth’s Climate Clock and Our Future
It’s now clear that what once seemed like an irregular pattern of ice ages and warm periods is actually a structured system driven by predictable astronomical forces. Study authors plan to build on their findings to create a baseline of Earth’s natural climate for the next 10,000-20,000 years. Used in combination with climate model simulations, researchers hope to quantify the exact effects of human-made climate change into the far future.
“Now we know that climate is largely predictable over these long timescales, we can actually use past changes to inform us about what could happen in the future,” Barker added. “This is something we couldn’t do before with the level of confidence that our new analysis provides.”
By understanding these natural cycles, scientists gain crucial context for evaluating how human activities are reshaping Earth’s climate system. This celestial clockwork has been ticking for millions of years, with ice sheets advancing and retreating across the Northern Hemisphere like a planetary heartbeat.
“This is vital for better informing decisions we make now about greenhouse gas emissions, which will determine future climate changes,” Barker concluded.
Paper Summary
Methodology
To solve this long-standing climate puzzle, the researchers took an innovative approach focused on the shape and timing of glacial-interglacial transitions rather than relying on precise absolute dating. They analyzed records of oxygen isotopes preserved in the shells of tiny marine organisms called benthic foraminifera, which reflect changes in global ice volume and deep ocean temperature. Using three independent data records with four different timescales, they identified key points in each glacial cycle: the onset of deglaciation, maximum rate of deglaciation, peak interglacial conditions, and maximum rate of glacial inception. By measuring the temporal offsets between these points and comparing them with the relative phasing of Earth’s orbital cycles (precession, obliquity, and eccentricity), they discovered strong correlations that revealed the distinct roles of each astronomical parameter. The team was able to overcome the problem of precise dating by looking at the shape of the climate record through time, allowing them to identify how the different parameters fit together to produce the climate changes observed.
Results
The analysis revealed several striking patterns that explain how Earth’s orbital variations drive glacial cycles. First, the researchers found that the offset between maximum deglaciation and peak interglacial conditions strongly correlates with the relative phasing of precession versus obliquity—explaining why some deglaciations are prolonged while others happen relatively quickly. Second, they discovered that all major glacial terminations over the past 900,000 years are associated with precession peaks that begin while obliquity is increasing, and specifically with the first such “candidate peak” to occur after each minimum in eccentricity. This pattern accurately predicted 10 out of 10 major glacial terminations in this time period. Third, they demonstrated that while precession dominates the early stages of deglaciation, obliquity controls the timing of peak interglacial conditions and subsequent glacial inception—with inception consistently occurring as obliquity decreases toward its minimum. The authors found that each glaciation of the past 900,000 years follows a predictable pattern—a discovery that confirms the natural climate change cycles observed on Earth over tens of thousands of years are largely predictable and not random or chaotic.
Limitations
While groundbreaking, the study has several limitations. The benthic oxygen isotope records used as proxies for ice volume also capture changes in deep ocean temperature, potentially introducing timing offsets between the recorded signal and actual ice volume changes. The researchers acknowledge this could affect their results by a few thousand years, though they argue this is relatively small compared to the variations in glacial cycle morphology they observed. Additionally, their focus on Northern Hemisphere ice sheets doesn’t fully account for Antarctic ice sheet contributions to global sea level, which could represent up to 15% of glacial-interglacial ice volume changes. The study also doesn’t address millennial-scale climate oscillations that might influence the exact timing of glacial transitions, though these could be incorporated into the broader framework they established. Finally, while their model works remarkably well for the past 900,000 years, it doesn’t apply to earlier periods when Earth’s climate followed different patterns, indicating that the relationship between orbital forcing and climate response has evolved over time.
Discussion and Implications
This research fundamentally changes our understanding of Earth’s glacial cycles by showing they are largely deterministic rather than chaotic. The predictable interplay between precession, obliquity, and eccentricity explains not only when ice ages begin and end but also their duration and intensity. This framework resolves several long-standing puzzles in paleoclimatology, including the “100,000-year problem” and the “Stage 11 problem.” By demonstrating that glacial inception depends primarily on obliquity, the study suggests that if not for anthropogenic CO₂, Earth would likely enter another glacial period within the next 10,000 years. This provides crucial context for understanding how human activities have disrupted the natural climate cycle. The research also challenges the traditional approach of using single insolation metrics to characterize orbital forcing, showing instead that the relative influence of precession versus obliquity changes as ice sheets grow and retreat across different latitudes. These findings represent a major contribution towards a unified theory of glacial cycles and provide a new baseline for understanding Earth’s natural climate variability.
Funding and Disclosures
The researchers noted in their paper that “this research was undertaken with no external funding,” making it a purely academic pursuit driven by scientific interest rather than targeted project funding. All authors contributed to various aspects of the research, including conceptualization, investigation, methodology, visualization, and writing. The paper acknowledged that this was contribution number 26 from the Cardiff EARTH CRediT initiative.
Publication Information
This study, titled “Distinct roles for precession, obliquity, and eccentricity in Pleistocene 100-kyr glacial cycles,” was authored by Stephen Barker, Lorraine E. Lisiecki, Gregor Knorr, Sophie Nuber, and Polychronis C. Tzedakis. It was published in Science on February 28, 2025 (Volume 387, Article eadp3491). The research represents a collaborative effort between scientists from Cardiff University, the University of California at Santa Barbara, Alfred Wegener Institute, and University College London. The paper was submitted on March 20, 2024, and accepted on January 18, 2025, with the DOI: 10.1126/science.adp3491.
