A pivotal discovery by an international consortium led by researchers at the University of Cambridge has pinpointed a critical climatic tipping point approximately 2.7 million years ago, marking a fundamental shift in Earth’s climate regime. Prior to this epoch, the planet experienced relatively warm and stable conditions with limited variability. However, this transition heralded the extensive expansion of continental ice sheets across the Northern Hemisphere, ushering in a new era characterized by pronounced cold snaps and volatile climate fluctuations on millennial timescales. This milestone elucidates how Earth’s glacial-interglacial cycles evolved from a relatively quiescent system into one marked by abrupt and frequent oscillations.
The team employed advanced geochemical analyses of sediment cores extracted from beneath the seafloor off the coast of Portugal during the International Ocean Discovery Program (IODP) Expedition 397. These sedimentary deposits, accumulating at a rapid and continuous rate, afford an unparalleled high-resolution archive of climate variability extending back over five million years—surpassing the temporal reach of polar ice cores by millions of years. By examining ratios of elements such as calcium, titanium, zirconium, and strontium, the researchers reconstructed detailed chronological profiles that capture the pace and intensity of ancient climate change with unprecedented precision.
Professor David Hodell, of Cambridge’s Department of Earth Sciences, who spearheaded the research, emphasized the significance of their findings: “Prior to 2.7 million years ago, the climate system exhibited minimal turbulence. However, at this juncture, we observe the emergence of the initial severe cold snaps, preceding a striking increase in the amplitude and frequency of climatic variability.” This period signaled the onset of rapid temperature swings occurring over mere millennia, coinciding with widespread intensification of Northern Hemisphere glaciation. These dynamic climate oscillations mirror patterns recorded in Greenland ice cores from the more recent Pleistocene Ice Age, underscoring the deep-time continuity of glacial climate processes.
A notable aspect of the study is the correlation between the onset of millennial-scale climate variability and the proliferation of ice-rafted debris detected in marine sediments. These rock fragments, carried by drifting icebergs and deposited as the icebergs melted, provide tangible evidence of expanding ice sheets that reached ocean margins. The calving of these marine-terminating glaciers likely disrupted oceanic circulation patterns, precipitating the abrupt and intense climate fluctuations observed in the sedimentary record. Such interactions highlight the complex feedback mechanisms linking cryospheric dynamics and global climate instability.
Importantly, the researchers determined that these rapid climate swings only materialized once glaciation surpassed a critical threshold—involving the scale of ice sheet growth, ocean temperature conditions, and sensitivities in ocean circulation systems. This confluence of factors created a “sweet spot” conducive to climate instability, imprinting a persistent millennial-scale variability onto the Earth’s climate system during the Quaternary Period. This discovery reframes our understanding of glacial climate as inherently variable rather than a monotonic cold phase, revealing the intricate interplay between ice volume and abrupt climate shifts.
The implications of this climatic transformation extend beyond geophysical parameters, intersecting with key junctures in human evolution. The timing of intensified glaciation and associated climate variability approximately aligns with the emergence of the genus Homo. This temporal coincidence suggests that early hominins may have been subjected to a highly heterogeneous environmental backdrop, requiring adaptive flexibility to survive fluctuating habitats and resource availability. This link between climate instability and evolutionary pressures provides compelling context for the shaping of hominin morphology, behavior, and dispersal patterns.
Methodologically, the exceptional sediment core records stem from a strategic ocean drilling site where sedimentation rates and preservation conditions facilitate continuous and finely resolved archives, rivaling the temporal resolution traditionally exclusive to ice cores. Unlike polar ice cores, which extend back roughly 800,000 years, these marine sediments extend well beyond this timeframe, enabling reconstructions of climate variability throughout the entire Quaternary and into the late Pliocene. This granular temporal resolution is vital for identifying abrupt events and transitions that govern climate system behavior over geological timescales.
The synthesis of geochemical proxies with stratigraphic markers of ice-rafted debris and paleoclimatic data integrates multidisciplinary lines of evidence to build a robust narrative of climate evolution. By establishing a consistent signal across diverse core sites, the study rules out localized disturbances, affirming that the recorded variability reflects hemispheric or global scale climatic phenomena. This widespread coherence strengthens interpretations of systemic climate mechanisms influenced by ice sheet dynamics, ocean circulation perturbations, and orbital forcing.
Further, these findings redefine the concept of glacial intensification as not merely an increase in ice volume or global cooling, but as an era when Earth’s climate acquired a capacity for heightened instability and rapid transitions. This system sensitivity bears profound implications for understanding present and future climate dynamics. Recognizing that Earth’s climate has operated within threshold-dependent regimes underscores the potential for tipping points that trigger sudden and dramatic environmental changes, a lesson increasingly pertinent in the context of anthropogenic climate perturbations.
The study, published in Science, contributes a crucial piece to the puzzle of Earth’s climatic past by extending the chronology of millennial variability deep into the Pliocene. It reveals that the interplay of ice sheet growth, oceanic conditions, and orbital cycles fostered a climate system predisposed to abrupt events well before the advent of modern homo sapiens. This history underscores the enduring influence of cryospheric changes on climate variability and sets a foundation for improved predictive models that incorporate natural thresholds and feedbacks.
Supported by the Natural Environment Research Council (NERC) under UK Research and Innovation (UKRI), this research exemplifies the power of international collaboration, advanced analytical techniques, and strategic ocean drilling expeditions in resolving fundamental questions about Earth’s climate system. As Professor Hodell remarked, “The sediment cores from off the Portuguese coast have revealed an unexpected clarity and detail of past climate signals, dramatically reshaping our understanding of when and how abrupt climatic fluctuations began to dominate.”
In sum, these revelations about the onset of millennial-scale climate variability highlight a transformative chapter in Earth’s climatic history, one that not only altered environmental conditions but also likely influenced the evolutionary trajectory of early hominins. The research invites a reexamination of the links between climate dynamics, ice sheet behavior, and biological evolution, offering insights that resonate well beyond geology and climatology into anthropology and human history.
Subject of Research: Climate change; Ice ages; Quaternary period; Human evolution
Article Title: Onset of millennial climate variability with the intensification of Northern Hemisphere glaciation
News Publication Date: 19-Feb-2026
Web References: https://doi.org/10.1126/science.ady7970
Image Credits: Carlos Alvarez Zarikian
