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Interglacial

An interglacial is a warm interval within an ice age characterized by relatively high global temperatures that cause glaciers and ice sheets to retreat, contrasting with colder glacial periods.^[1] These periods typically last between 10,000 and 30,000 years and are marked by rising sea levels due to ice melt, increased atmospheric CO₂ concentrations, and more stable, wetter climates compared to glacials.^[2]^[1] Interglacials occur as part of recurring glacial-interglacial cycles driven primarily by Milankovitch cycles—variations in Earth's orbital eccentricity, axial tilt (obliquity), and precession—which modulate the amount of solar radiation reaching the Northern Hemisphere during summer months.^[1]^[2] These orbital changes initiate warming, which is amplified by feedbacks such as reduced ice-albedo effects (less reflective ice surface) and the release of CO₂ from oceans, leading to temperatures 4–7°C higher than during glacials over several thousand years.^[3]^[2] In the late Quaternary, over the past about 800,000 years, these cycles have occurred roughly every 100,000 years, with interglacials representing the warmer phases amid overall cooling trends.^[2]^[4] The most recent interglacial, known as the Holocene Epoch, began approximately 11,500 years ago following the retreat of the last glacial maximum, which had peaked around 21,000–26,000 years earlier.^[2]^[1] During past interglacials, such as the Sangamonian (about 130,000–110,000 years ago), temperatures were comparable to or slightly warmer than today's, supporting diverse ecosystems and human migration patterns.^[5]^[3] Paleoclimate records from ice cores, like those from Antarctica's Dome Fuji, reveal that CO₂ levels during interglacials typically ranged from 260–280 parts per million, facilitating the expansion of forests and grasslands over tundra.^[2] Today, Earth remains in the Holocene interglacial, but ongoing anthropogenic warming is accelerating temperature rises at rates far exceeding natural interglacial transitions—approximately 10 times faster than the 4–7°C warming over 5,000 years at the end of previous ice ages.^[3] This rapid change raises questions about the stability of current interglacial conditions and potential transitions to future glacial states, though human-induced greenhouse gas emissions may prolong or disrupt the cycle.^[2] Interglacials have profoundly shaped Earth's biota, with evidence from sediment and fossil records showing adaptations in flora, fauna, and early human societies to these dynamic climates.^[5]

Definition and Characteristics

Definition

An interglacial period is a geological interval of relatively warm climate that occurs between successive glacial periods within an ice age, marked by the partial or complete retreat of continental ice sheets and a corresponding rise in global sea levels due to reduced ice volume.^[6] These periods represent the warmer end-members of glacial-interglacial cycles, during which temperatures are elevated compared to the preceding and following glacial phases, allowing for expanded ecosystems and minimal extent of land-based ice. Interglacials differ from interstadials, which are briefer and milder warm episodes embedded within a broader glacial period, lacking the duration or intensity needed for significant ice sheet retreat or the development of full interglacial conditions.^[6] While interstadials may involve temporary warming and localized glacier recession, they do not transition the climate to a state incompatible with widespread glaciation, as defined by stratigraphic and paleoclimatic criteria.^[7] The term "interglacial" emerged in 19th-century geology to denote these warm phases, coined by Swiss naturalist Oswald Heer in 1865 based on the identification of temperate-climate sediments and fossils interbedded between glacial deposits in Alpine regions.^[8] This nomenclature was soon adopted and refined by geologists like Archibald Geikie, who in 1874 applied it to describe post-glacial warm intervals in British stratigraphic sequences, establishing its use in reconstructing Quaternary climate history.^[8]

Key Characteristics

Interglacial periods are marked by a substantial rise in global mean surface temperatures, typically 4–7°C warmer than during glacial maxima, as evidenced by paleoclimate reconstructions from ice cores and marine sediments.^[9] This warming drives partial or near-complete deglaciation, with major Northern Hemisphere ice sheets retreating significantly, though polar ice caps like those in Greenland and Antarctica persist in reduced form.^[10] Such temperature increases, often initiated by orbital variations known as Milankovitch cycles, fundamentally alter the Earth's energy balance and set the stage for broader climatic shifts.^[9] A hallmark of interglacials is the consequent sea-level rise of approximately 120–130 meters relative to glacial lows, primarily from the melting of continental ice sheets and, to a lesser extent, thermal expansion of seawater.^[11] This eustatic change reshapes coastlines, inundates continental shelves, and influences sediment dynamics and marine habitats worldwide.^[11] Warmer conditions facilitate the expansion of temperate forests into higher latitudes and elevations, replacing tundra and steppe biomes that dominated during glacials, while overall terrestrial biodiversity increases due to expanded habitable ranges and diverse ecosystems.^[12] In marine realms, shifts in ocean circulation patterns occur, including the strengthening of the Atlantic Meridional Overturning Circulation (AMOC), which enhances heat transport to the North Atlantic and supports productive upwelling zones.^[13] These periods generally last 10,000–30,000 years, with the peak warmth, or climatic optimum, persisting for 5,000–10,000 years before gradual cooling resumes.^[1] This temporal structure allows ecosystems to stabilize and evolve, though transitions to subsequent glacials can introduce variability.^[14]

Causes and Mechanisms

Orbital Forcing

Orbital forcing refers to the periodic variations in Earth's orbit and axial orientation, collectively known as Milankovitch cycles, which primarily drive the initiation of interglacial periods by altering the distribution and intensity of solar insolation reaching Earth's surface.^[15] These cycles modulate incoming solar radiation, with changes up to 25% at certain latitudes, influencing the growth and retreat of ice sheets over tens of thousands of years.^[15] The eccentricity cycle, occurring approximately every 100,000 years, describes the shape of Earth's orbit around the Sun, varying from nearly circular to more elliptical.^[15] This variation affects the Earth-Sun distance, leading to differences in solar insolation of up to 23% at perihelion (closest approach) compared to aphelion (farthest point), though its direct impact on seasonal climate is relatively minor without interaction with other cycles.^[15] The obliquity cycle, with a period of about 41,000 years, governs the tilt of Earth's rotational axis, ranging from 22.1° to 24.5°.^[15] Greater tilts increase seasonal contrasts, particularly enhancing summer insolation at high latitudes and favoring ice melt during interglacial onsets.^[15] Precession, cycling every roughly 23,000 years, involves the wobble of Earth's axis and the precession of the equinoxes, shifting the timing of seasons relative to the orbit's closest and farthest points.^[15] This alters the peak seasonal insolation, with Northern Hemisphere summers aligning more closely with perihelion to amplify warming.^[15] When these cycles align to produce peaks in summer insolation at high northern latitudes, such as 65°N, they initiate interglacial warming by reducing ice cover and triggering ice-albedo feedback, where melting exposes darker surfaces that absorb more sunlight.^[15] These insolation maxima, rather than global averages, are critical for glacial termination, as they preferentially affect Northern Hemisphere ice sheets.^[16] The basic mathematical representation of absorbed insolation at Earth's surface is given by Q = \frac{S}{4} (1 - A), where S is the solar constant (approximately 1366 W/m²) and A is planetary albedo; orbital parameters primarily influence the latitudinal and seasonal distribution of Q rather than its global mean.^[17] This qualitative shift in insolation patterns underscores the astronomical basis for interglacial transitions without requiring detailed derivations.^[15]

Feedback and Other Influences

The initiation of interglacial warming, primarily driven by orbital forcing, is amplified and sustained through various feedback mechanisms and secondary influences that enhance atmospheric and oceanic heat retention. One key amplifying process is the ice-albedo feedback, where initial warming causes the retreat of continental ice sheets and sea ice, reducing Earth's surface reflectivity (albedo) from approximately 0.6–0.8 for ice-covered areas to 0.1–0.3 for exposed land and ocean surfaces. This decrease allows greater absorption of incoming solar radiation, which further accelerates melting and warming, contributing significantly to the temperature rise observed during transitions to interglacials. Model simulations indicate that this feedback can account for up to 50% of the total hemispheric warming in high latitudes during these periods. Changes in the carbon cycle further intensify interglacial warmth by releasing stored greenhouse gases from terrestrial and marine reservoirs. As temperatures rise, warming soils and permafrost thaw, promoting microbial decomposition of organic matter and emitting carbon dioxide (CO₂) and methane (CH₄); permafrost regions alone hold about 1,300–1,600 gigatons of organic carbon, with deglacial thawing contributing to abrupt CH₄ pulses. Simultaneously, ocean warming reduces the solubility of CO₂ in seawater and alters circulation patterns, leading to outgassing that elevates atmospheric CO₂ levels to peaks of 280–300 parts per million (ppm) and CH₄ to around 700–800 parts per billion (ppb) during interglacial maxima. These increases enhance the greenhouse effect, prolonging warm conditions for millennia.^[18]^[19]^[20] Shifts in ocean circulation also play a role in redistributing heat to polar regions, sustaining interglacial climates. During interglacials, the opening of gateways like the Bering Strait due to rising sea levels facilitates increased influx of relatively warmer, low-salinity Pacific water into the Arctic Ocean, at rates up to 1–2 Sverdrups, which stratifies the water column and reduces sea ice formation while transporting heat northward. This throughflow weakens the Atlantic Meridional Overturning Circulation slightly but enhances overall Arctic heat budget, contributing to regional warming of 2–4°C in the northern high latitudes.^[21]^[22] Volcanic eruptions and solar variability act as minor modulators of interglacial conditions, introducing short-term perturbations rather than driving long-term trends. Large volcanic events can temporarily cool the planet by 0.5–1°C for 1–3 years through stratospheric aerosol injection, potentially delaying peak warmth, while solar irradiance fluctuations of about 0.1–0.2% over decadal cycles influence surface temperatures by less than 0.1°C globally, insufficient to alter the primary orbital and feedback-dominated patterns.^[23]^[24]

Geological Context

Glacial-Interglacial Cycles

Glacial-interglacial cycles constitute the primary rhythm of Earth's climate over the late Quaternary, featuring prolonged cold phases with expanded continental ice sheets (glacials) interspersed with shorter warm intervals of ice retreat and elevated global temperatures (interglacials). These cycles exhibit periodicities ranging from 41,000 to 100,000 years, reflecting a shift from obliquity-dominated cycles in the early Pleistocene to eccentricity-modulated 100,000-year cycles in the late Pleistocene.^[25]^[26] Within a typical 100,000-year cycle, glacial periods endure for 70,000 to 90,000 years, while interglacials persist for 10,000 to 30,000 years.^[27] This asymmetry in duration underscores the stability of cold states relative to the more transient warm phases.^[6] The cycles are identified and dated using Marine Isotope Stages (MIS), a chronostratigraphic framework based on variations in the oxygen isotope ratio (δ¹⁸O) recorded in the calcite shells of benthic foraminifera from marine sediments. Even-numbered MIS denote glacial intervals, characterized by elevated δ¹⁸O values that signal greater global ice volume and lower deep-ocean temperatures, whereas odd-numbered MIS indicate interglacials with depleted δ¹⁸O reflecting diminished ice sheets and warmer seas.^[28]^[29] This isotopic proxy effectively captures the waxing and waning of ice sheets, providing a global index of paleoclimate oscillations.^[30] Paleoclimate evidence for these cycles derives from diverse archives that collectively demonstrate their global coherence and pacing. Deep-sea sediment cores offer high-resolution records of benthic δ¹⁸O and other proxies, revealing the sequential buildup and decay of ice volumes over multiple cycles.^[31] Ice cores from polar regions, such as those in Antarctica spanning the last 800,000 years, preserve trapped air bubbles and isotopic signals in ice layers, corroborating atmospheric and temperature shifts aligned with MIS.^[9] Loess deposits, wind-blown silts accumulated in mid-latitude continental interiors like the Chinese Loess Plateau, further attest to intensified aridity and dust transport during glacials, with paleosols forming in interglacials.^[32] Transitions between these states unfold symmetrically over 5,000 to 10,000 years, encompassing progressive changes in ice extent, sea level, and biosphere distribution.^[33]^[34]

Quaternary Period Overview

The Quaternary Period, spanning from approximately 2.58 million years ago to the present, represents the current geological period characterized by repeated episodes of cooling and warming that define the ongoing ice age.^[35] This era is distinguished by the initial onset of significant Northern Hemisphere glaciation around 2.7 million years ago, which marked a shift toward persistent ice sheet development in regions like Greenland and North America, driven by declining atmospheric CO₂ levels and tectonic changes such as the closure of the Isthmus of Panama.^[36] The period encompasses the Pleistocene Epoch, ending about 11,700 years ago, and the ongoing Holocene Epoch, during which glacial-interglacial oscillations have shaped global climate patterns.^[35] Throughout the Quaternary, the climate has been dominated by roughly 50 glacial-interglacial cycles, reflecting rhythmic expansions and contractions of ice sheets primarily in the Northern Hemisphere.^[37] These cycles underwent a major reorganization during the Mid-Pleistocene Transition around 1 million years ago, when the dominant periodicity shifted from obliquity-driven 41,000-year cycles to eccentricity-modulated 100,000-year cycles, accompanied by an increase in cycle amplitude that resulted in more extensive glaciations.^[38] Prior to this transition, cycles were generally milder and more frequent, while post-transition cycles featured prolonged glacial phases with greater ice buildup, influencing sea levels, ocean circulation, and terrestrial ecosystems worldwide.^[38] Global ice volume during Quaternary glacial maxima fluctuated dramatically, reaching up to 3–4 times modern levels as inferred from variations in benthic foraminiferal oxygen isotope ratios (δ¹⁸O) in deep-sea sediments, which record both seawater temperature and the δ¹⁸O enrichment due to ice sheet growth. For instance, during the Last Glacial Maximum around 21,000 years ago, equivalent to Marine Isotope Stage 2, ice volume expansion lowered sea levels by approximately 120–130 meters compared to today, underscoring the scale of these fluctuations. These ice volume changes, detailed further in discussions of glacial-interglacial cycles, amplified climate feedbacks such as albedo effects and carbon cycling.

Pleistocene Interglacials

Cycle Patterns in the Pleistocene

The Pleistocene epoch, from 2.58 million years ago to 11.7 thousand years ago, encompassed approximately 20 major interglacials as part of broader glacial-interglacial cycles.^[39] These cycles exhibited distinct tempo shifts: early Pleistocene interglacials were primarily paced by the 41,000-year obliquity cycle of Earth's axial tilt, resulting in relatively frequent but modest climate oscillations.^[27] Following the Mid-Pleistocene Transition (MPT) around 1.2 to 0.7 million years ago, the dominant rhythm transitioned to the 100,000-year eccentricity cycle, characterized by longer intervals between interglacials and more pronounced climate variability.^[40] This MPT marked a fundamental change in the pacing and amplitude of cycles, with pre-MPT interglacials showing smaller global temperature swings compared to the intensified late Pleistocene ones.^[41] Interglacial intensity during the Pleistocene displayed clear variability, with early episodes generally weaker than those in the mid- to late stages.^[27] Evidence from pollen records reveals limited forest expansion during early interglacials, reflecting subdued warming and restricted vegetative shifts from tundra to woodland, whereas mid- and late Pleistocene interglacials show more extensive pollen assemblages indicative of widespread broadleaf and coniferous forest growth.^[42] Similarly, mammal fossils provide biostratigraphic support, with early interglacial faunas dominated by cold-adapted species and limited diversity, contrasting with later periods where warm-climate herbivores and forest-dwelling taxa proliferated, signaling stronger ecological responses to peak warmth.^[43] Regional patterns in Pleistocene interglacials were markedly asymmetric, with the strongest expressions occurring in the Northern Hemisphere due to the influence of expansive ice sheets.^[44] The Laurentide Ice Sheet over North America and the Fennoscandian Ice Sheet over northern Europe drove amplified warming and sea-level rise during deglaciations, leading to more dramatic vegetation and faunal changes in these areas compared to the Southern Hemisphere, where Antarctic ice responded more gradually.^[45] This hemispheric contrast underscores how Northern Hemisphere ice dynamics amplified the overall tempo and variability of interglacial cycles across the epoch.^[46]

Notable Examples

The Eemian interglacial, corresponding to Marine Isotope Stage (MIS) 5e from approximately 130 to 115 thousand years ago (ka), represents one of the most intensively studied Pleistocene warm periods, characterized by peak global temperatures about 2°C warmer than pre-industrial modern levels.^[47] Proxy records from ice cores and marine sediments indicate sustained warmth driven by high orbital insolation, leading to significant ice sheet retreat. Sea levels during this peak rose 5–9 meters above present, as evidenced by coral reef terraces and shoreline indicators in tectonically stable regions like the Bahamas and Western Australia. In Europe, this warmth supported subtropical fauna, including hippopotamus (Hippopotamus amphibius) fossils discovered in riverine deposits along the Thames Valley in southern England, indicating river temperatures suitable for such species.^[48] Pollen assemblages from lake and bog sites across the North European Plain reveal dominance of oak (Quercus) and hazel (Corylus) forests, reflecting temperate woodland expansion into areas now glaciated.^[49] The Hoxnian interglacial, aligned with MIS 11 from about 424 to 374 ka, stands out for its prolonged duration of roughly 50,000 years, comparable in length to the Holocene but occurring under lower summer insolation.^[50] This extended warmth is documented in lacustrine sequences from sites like Hoxne in East Anglia, England, where organic-rich sediments preserve evidence of stable climatic conditions over multiple millennia.^[51] Faunal remains, particularly fossils of the straight-tusked elephant (Palaeoloxodon antiquus), are abundant in Hoxnian deposits across Britain and continental Europe, suggesting open woodland habitats with access to grasslands and water sources.^[52] These megafaunal assemblages, combined with pollen data indicating mixed deciduous and coniferous forests, highlight a period of ecological stability that supported diverse large mammal populations.^[53] MIS 7e, spanning roughly 242 to 230 ka, marked a climatic optimum within the more variable MIS 7 complex, with temperatures fluctuating but reaching levels comparable to early Holocene warmth in some regions.^[6] Marine sediment cores from the North Atlantic and Mediterranean show oscillatory patterns in sea surface temperatures, reflecting instability possibly linked to ice sheet dynamics.^[54] Atmospheric CO₂ concentrations, reconstructed from ice core proxies and benthic foraminifera, stabilized around 280 parts per million (ppm) during this substage, consistent with other mid-Pleistocene interglacials.^[9] Terrestrial evidence from western European pollen records indicates temperate forest expansion, though interrupted by cooler phases, underscoring the substage's role as a transitional warm interval.^[55] Earlier interglacials like MIS 13 (approximately 524–474 ka) provide insights into pre-Mid-Pleistocene Transition dynamics, with evidence from lake sediments in southern Europe revealing boreal forest expansion into mid-latitudes.^[56] Pollen profiles from the Lirino Lake basin at Ceprano, Italy, document shifts from steppe-tundra to conifer-dominated woodlands, including pine (Pinus) and birch (Betula), indicating warmer, moister conditions than preceding glacials.^[57] These continental records correlate with marine isotope data showing reduced ice volume, supporting a period of relative climatic mildness despite lower orbital forcing compared to later interglacials.^[56]

Holocene Interglacial

Onset and Early Holocene

The Holocene interglacial commenced approximately 11,700 calibrated years before present (cal yr BP), coinciding with the abrupt termination of the Younger Dryas stadial, a period of cold climate that had interrupted the broader deglaciation trend.^[58] This transition was characterized by rapid warming during the Preboreal oscillation, following the earlier Bølling-Allerød interstadial (14.7–12.9 ka), with Northern Hemisphere temperatures rising by several degrees Celsius over decades to centuries, driven by enhanced Atlantic Meridional Overturning Circulation and reduced ice-albedo feedback.^[59] Proxy records from ice cores and lake sediments indicate that this warming initiated widespread environmental reorganization, ending the last glacial-interglacial cycle's cold reversal and establishing the stable warm conditions of the current interglacial.^[60] During the early Holocene (11.7–8.2 ka), accelerated melting of the Laurentide and Fennoscandian ice sheets led to substantial global mean sea-level rise, estimated at around 35–40 meters over the broader early period to 3 ka, with peak rates exceeding 8 mm per year around 10–8 ka associated with meltwater pulses from North American and Antarctic ice complexes.^[61] This rapid deglaciation exposed new landmasses and altered coastal ecosystems, while continental interiors experienced greening as permafrost thawed and hydrology shifted. Vegetation assemblages responded dynamically, with pollen records documenting the northward migration and expansion of temperate broadleaf forests—dominated by species such as oak, hazel, and elm—in Europe and eastern North America, replacing late-glacial tundra and open parklands as summer temperatures peaked 1–2°C above present levels.^[62] In North America, this afforestation amplified regional warming through biogeophysical feedbacks, enhancing moisture retention and carbon sequestration in newly stabilized soils.^[63] Preceding the mid-Holocene climatic optimum, the early Holocene saw strengthening of the African monsoon system between 9 and 6 ka, fueled by high Northern Hemisphere summer insolation and orbital precession, which shifted the Intertropical Convergence Zone northward and increased summer rainfall by up to 400–600 mm annually in subtropical regions.^[64] This intensification transformed the Sahara into a "Green Sahara" landscape, with lacustrine and aeolian records evidencing widespread savanna expansion, lake filling, and fluvial activity across North Africa, supporting diverse flora and fauna including grasslands and wetlands.^[65] These changes not only boosted regional biodiversity but also influenced global dust fluxes and atmospheric circulation, setting the stage for peak interglacial warmth.^[66]

Mid-to-Late Holocene Variations

The Mid-to-Late Holocene, spanning approximately 9 to 0 ka, featured notable climatic variations superimposed on the broader warming trend from the early Holocene. A prominent warm interval known as the Holocene Climatic Optimum occurred between 9 and 5 ka, characterized by peak temperatures 1–2°C above modern levels in regions such as subtropical East Asia and the North Atlantic.^[67] This period coincided with a mid-Holocene sea-level highstand of 2–3 m above present levels in areas like South China, driven by thermal expansion and residual ice melt from the waning Pleistocene.^[67] Paleoclimate proxies, including pollen records and lake sediments, indicate enhanced monsoon activity and expanded vegetation zones during this optimum, reflecting stronger summer insolation in the Northern Hemisphere.^[68] Following the Holocene Climatic Optimum, the onset of Neoglaciation around 5 ka marked a shift to gradual cooling and increased moisture in mid-to-high latitudes, persisting to the present.^[69] This cooling trend, attributed to declining orbital insolation and amplified by feedback mechanisms like expanded sea ice, led to the reformation and advance of alpine glaciers across the European Alps and other mountain ranges.^[70] Within this neoglacial framework, a temporary warm episode—the Medieval Climate Anomaly—emerged between approximately 950 and 1250 CE, with temperatures in parts of the North Atlantic and Europe approaching or exceeding early modern values, as evidenced by Norse settlement expansions in Greenland.^[71] Glacier retreats during this anomaly were regionally variable, but the overall neoglacial cooling resumed thereafter, culminating in more persistent ice advances by the late medieval period.^[72] The Little Ice Age, from roughly 1250 to 1850 CE, represented the most pronounced cooling phase within Neoglaciation, with global temperatures dropping 0.5–1°C below the preceding centuries in the Northern Hemisphere.^[73] This interval featured severe winters, including multiple Thames River frost fairs in London between the 16th and 18th centuries, alongside widespread alpine glacier expansions and crop failures.^[74] The cooling is linked to a combination of reduced solar irradiance during minima like the Maunder Minimum (1645–1715 CE) and increased volcanic aerosol loading from eruptions such as Huaynaputina in 1600 CE, which enhanced atmospheric reflectivity and shortened growing seasons.^[73] Tree-ring and ice-core records confirm these forcings drove hemispheric-scale anomalies, with the most intense cooling centered around 1650–1710 CE.^[75]

Current and Future Interglacials

Anthropogenic Influences on the Current Interglacial

Since the Industrial Revolution, human activities, primarily the burning of fossil fuels, deforestation, and industrial processes, have driven a significant increase in atmospheric carbon dioxide (CO₂) concentrations from pre-industrial levels of approximately 280 parts per million (ppm) to approximately 427 ppm as of November 2025.^[76]^[77] This rapid rise has accelerated global warming rates far beyond the natural variability observed during previous interglacials, including the stable or slightly cooling trends of the mid-to-late Holocene. The enhanced greenhouse effect from elevated CO₂ and other anthropogenic greenhouse gases has resulted in an average global temperature increase of approximately 1.2°C since pre-industrial times, with projections indicating further escalation if emissions continue unabated.^[78] Comparisons with past interglacials, such as the Eemian (approximately 130,000–115,000 years ago), highlight the unprecedented speed of current warming. The onset of the Eemian interglacial involved a global temperature rise of 4–7°C over several thousand years following the Last Glacial Maximum, at an average rate about 10 times slower than the observed warming over the past century.^[9] In contrast, anthropogenic forcing has propelled recent decadal warming rates to around 0.2°C per decade, outpacing natural deglaciation transitions and altering the Holocene's thermal trajectory. This accelerated warming carries the potential to avert the onset of the next glacial period; model simulations suggest that cumulative anthropogenic CO₂ emissions of 1,000–1,500 gigatonnes of carbon could delay glacial inception by at least 50,000 years, effectively prolonging the current interglacial indefinitely under high-emission scenarios.^[79] These human-induced changes are profoundly impacting interglacial dynamics through various feedbacks and direct effects. Global mean sea level has risen at an accelerating rate, reaching 3.7 mm per year between 2006 and 2018, driven by thermal expansion and melting land ice—rates far exceeding those during stable phases of prior interglacials and contributing to coastal inundation and habitat displacement.^[80] Biodiversity is experiencing substantial losses, with climate change exacerbating habitat fragmentation, species extinctions, and ecosystem shifts; for instance, up to 50% of species in vulnerable regions face high extinction risks under continued warming, as observed in terrestrial, freshwater, and marine biomes.^[81] Additionally, anthropogenic warming is disrupting natural cycle feedbacks, notably through permafrost thaw in the Arctic, where human-caused temperature increases have accelerated the release of stored methane and CO₂, potentially amplifying global warming by 0.13–0.27°C by 2100 under moderate emission pathways.^[82]

Predictions for Future Transitions

Scientific models based on Milankovitch cycles project the natural onset of the next glacial period following the Holocene interglacial to occur between approximately 4,300 and 11,100 years from the present, driven by declining summer insolation at high northern latitudes due to orbital variations in precession and obliquity. However, anthropogenic carbon dioxide emissions have significantly altered this trajectory, with current atmospheric CO2 levels already sufficient to delay glacial inception by tens of thousands of years, potentially pushing full glacial conditions beyond 50,000 years into the future. Recent studies, such as Barker et al. (2024), confirm that emissions exceeding 1.5 trillion tonnes of CO₂ could delay the next glaciation by 100,000 years or more.^[83] Simulations using coupled climate-carbon cycle models demonstrate that persistent elevated CO2 from fossil fuel combustion overrides the cooling effects of orbital forcing. In particular, Archer and Ganopolski (2005) found that even moderate emissions of 300 gigatons of carbon could delay the next glaciation by about 140,000 years, while higher emissions exceeding 5,000 gigatons of carbon might prevent it for over 500,000 years by maintaining temperatures above the threshold for ice sheet growth at 65°N.^[84] This long-term CO2 persistence— with roughly 25% remaining in the atmosphere for millennia and 7% enduring beyond 100,000 years—effectively raises the insolation threshold required to trigger glaciation, simulating conditions akin to a "movable trigger."^[85] Under scenarios where emissions stabilize at low levels (e.g., around 500 petagrams of carbon), models predict glacial inception delayed to beyond 50,000 years from now, though full glacial conditions would still be postponed to at least 120,000 years, allowing for partial ice sheet development only after significant CO2 drawdown.^[86] In contrast, continued high emissions (e.g., 3,000 petagrams of carbon) could extend the ice-free Northern Hemisphere for approximately 600,000 years, resulting in a prolonged warm interglacial state with global temperatures remaining approximately 0.5°C above pre-industrial levels after 500,000 years.^[86] These projections highlight the dominant role of human-induced greenhouse gases in reshaping Quaternary climate cycles.^[79]

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Volcanic and Solar Forcing of Climate Change during the ...
The climate response to variability in volcanic aerosols and solar irradiance, the primary forcings during the preindustrial era, is examined in a ...Missing: interglacial | Show results with:interglacial
[23]
The effects of changing solar activity on climate
Jul 24, 2012 · In this review paper, we present palaeoclimatological evidence for the past influence of solar variability on Earth's climate, highlighting the effects of ...
[24]
Interglacials of the Quaternary defined by northern hemispheric land ...
Oct 12, 2020 · Glacial/interglacial dynamics during the Quaternary were suggested to be mainly driven by obliquity (41-kyr periodicity), ...
[25]
Orbital-accelerated transient simulations of glacial-interglacial ...
Jun 9, 2025 · In the past 800,000 years, the Earth's climate system has undergone alternating glacial and interglacial periods with a major cycle of 100,000 ...
[26]
Astronomical forcing shaped the timing of early Pleistocene glacial ...
May 15, 2023 · The duration of the interglacial periods ranges from 10 to 30 kyr (i.e., 0.5–1.5 precession cycles). For MIS 45, 43 and 41, the interglacial ...
[27]
Orbital control of western North America atmospheric circulation and ...
May 2, 2014 · ... glacial marine isotope stages (MIS). We use these stages here, defined by the ice volume proxy of marine benthic δ18O values, as a ...
[28]
SIDEBAR. The Mid-Pleistocene Enigma - The Oceanography Society
Aug 19, 2020 · Marine Isotope Stages (MIS) discussed in text are annotated, and the ... Even numbers represent cold glacial periods and odd numbers represent ...
[29]
A global synthesis of high-resolution stable isotope data ... - Nature
Mar 10, 2023 · Benthic foraminiferal δ13C and δ18O data from global marine sediment core sites were collected from on-line repositories, original ...
[30]
Paleoclimatology: Explaining the Evidence - NASA Earth Observatory
May 9, 2006 · Ocean cores showed that the Earth passed through regular ice ages—not just the 3 or 4 recorded on land by misplaced boulders and glacial loess ...
[31]
Orbital-accelerated transient simulations of glacial-interglacial ...
Jun 9, 2025 · Proxy records reveal divergent orbital controls on Asian monsoon systems: (1) Chinese loess deposits link glacial-interglacial cycles (~100-kyr) ...
[32]
How is the current global warming trend different from ... - Climate
Jan 23, 2014 · The transition from the last ice age to the current interglacial period is estimated to have spanned 5,000 years.
[33]
Interglacials of the 41 ka-world and the Mid-Pleistocene Transition
Before ~1.25 million years ago (Ma), glacial-interglacial cycles appear symmetric ... The MPT, referring both to the change in frequency and intensity of glacial ...
[34]
[PDF] Geologic Map of Great Sand Dunes NAtional Park, Colorado
Deposits of Quaternary age (time between the present and. 2.58 million years ... The Quaternary Period includes the Pleistocene Epoch (2.58 Ma to 11.7 ka).
[35]
How the Isthmus of Panama Put Ice in the Arctic
Mar 22, 2004 · The onset of Northern Hemisphere glaciation also affected the Subarctic Pacific. It led to the formation about 2.7 million years ago of a ...
[36]
[PDF] On The Nature of Ice Ages
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[37]
Evidence for a Northern Hemispheric trigger of the 100000-y glacial ...
Nov 8, 2021 · Causes of the Mid-Pleistocene Transition (MPT) from 41- to 100-ky interglacial–glacial cyclicity are debated because it occurred without changes ...
[38]
The Mid-Pleistocene Transition: a delayed response to an ... - NIH
The Mid-Pleistocene Transition (MPT) marks a shift of the dominant periodicity of these climate cycles from ∼ 40 to ∼ 100 kyr.
[39]
Mid-Pleistocene revolution and the 'eccentricity myth'
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[40]
Pollen from the Deep-Sea: A Breakthrough in the Mystery of the Ice ...
Jan 25, 2018 · The magnitude of the Atlantic forest expansion during different interglacials will mainly reflect the amplitude of the warming above 40°N ...
[41]
Differentiation of the British late Middle Pleistocene interglacials
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[42]
[PDF] glacial cycles' toward a new paradigm
role. This symmetric warming at both poles may induce a substantial global climatic effect. Indeed, the strong sim- ilarity between ...
[43]
Modeling of the northern hemisphere ice sheets during the last ...
Apr 7, 2005 · We present a new three-dimensional thermomechanically coupled ice sheet model of the northern hemisphere to reconstruct the Quaternary ice ...
[44]
A new global ice sheet reconstruction for the past 80 000 years
Feb 23, 2021 · Fluctuations in sea level for the past 80,000 years are dominated by changes in the Laurentide Ice Sheet, so it is most sensitive to ice sheet ...Missing: stronger | Show results with:stronger<|control11|><|separator|>
[45]
A global mean sea surface temperature dataset for the Last ...
Dec 10, 2020 · A global mean sea surface temperature dataset for the Last Interglacial (129–116 ka) and contribution of thermal expansion to sea level change.
[46]
Hippos on the Thames – The Story of the Warm Stages | Request PDF
The bones were discovered in 1930 by amateur archaeologist Gustav Adolf Spengler in a gravel pit in Edersleben and excavated and recovered by him and his son in ...
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The history of vegetation of the Eemian Interglacial in the Great ...
Aug 7, 2025 · The subject of this paper is the history of vegetation in the Eemian Interglacial in southern Great Poland determined in the course of ...
[48]
New evidence for complex climate change in MIS 11 from Hoxne ...
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[49]
Holsteinian Interglacial=Marine Isotope Stage 11? | Request PDF
Aug 6, 2025 · The Holsteinian interglacial is considered to be a significantly long warm period during the Middle Pleistocene (Melles et al., 2012) and has ...
[50]
[PDF] The straight-tusked elephant (Palaeoloxodon antiquus) in ...
This thesis examines the evolution of the straight-tusked elephant {Palaeoloxodon antiquus) in Pleistocene Europe where it was a conspicuous interglacial faunal ...
[51]
Differentiation of the British late Middle Pleistocene interglacials
Aug 6, 2025 · Here, some 200,000 years ago, mammoths, straight-tusked elephants, lions, and other animals roamed across grasslands with scattered trees ...
[52]
Simulating Marine Isotope Stage 7 with a coupled climate–ice sheet ...
Nov 13, 2020 · This study simulates the glacial buildup from MIS 7 to 6 using a coupled model, finding glacial inceptions are more sensitive to orbital ...<|control11|><|separator|>
[53]
Comparative carbon cycle dynamics of the present and last interglacial
Apr 1, 2016 · In the last interglacial period (Eemian), CO2 varied around the level of about 270–280 ppm without any significant trend from 126 to 115 ka BP ( ...
[54]
The MIS 13 Interglacial at Ceprano, Italy, in the Context of Middle ...
100 m a.s.l., MIS 13 is part of a lacustrine sediment succession deposited during the Early-Middle Pleistocene within the extinct Lirino Lake. The pollen data ...
[55]
Western European paleoenvironmental fluctuations across MIS 13–11
Marine Isotope Stages (MIS) 13–11 saw a major transformation in the hominin occupation of Europe, with an expansion in the scale and geographical distribution ...
[56]
Worldwide Late Pleistocene and Early Holocene population ... - Nature
Nov 24, 2023 · The worldwide extinction of megafauna during the Late Pleistocene and Early Holocene is evident from the fossil record, with dominant ...
[57]
Past permafrost dynamics can inform future permafrost carbon ...
Jul 25, 2023 · Rapid warming during the Bølling-Allerød (14.7–12.8 ka) and Younger Dryas-Preboreal transition (11.7–~10 ka) shows evidence of some of the ...Permafrost History And... · Glacial-Interglacial... · Permafrost Thaw And Carbon...<|separator|>
[58]
Abrupt climate changes in the last two deglaciations simulated with ...
Nov 25, 2021 · We show that a set of abrupt climate changes of the last deglaciation, including Bolling–Allerod warming, the Younger Dryas, and onset of the Holocene were ...
[59]
Global sea-level rise in the early Holocene revealed from ... - Nature
Mar 19, 2025 · Here we present an early Holocene sea-level curve based on 88 sea-level data points (13.7–6.2 thousand years ago (ka)) from the North Sea (Doggerland).
[60]
Europe's lost forests: a pollen-based synthesis for the last ... - Nature
Jan 15, 2018 · 8000 years ago, prior to Neolithic agriculture, Europe was mostly a wooded continent. Since then, its forest cover has been progressively ...
[61]
The deglacial forest conundrum | Nature Communications
Oct 13, 2022 · Here we report a conundrum: Deglacial forest expansion in the NH extra-tropics occurs approximately 4000 years earlier in a transient MPI-ESM1.2 simulation.Missing: broadleaf | Show results with:broadleaf
[62]
North African humid periods over the past 800,000 years - Nature
Sep 8, 2023 · Proxy evidence for the Holocene NAHP indicates an increase ranging from ~400 mm/yr (15-30°N, 10°W:30°E) to 640 mm/yr in the Western Sahara (15– ...
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End of Green Sahara amplified mid- to late Holocene megadroughts ...
Aug 21, 2020 · We report evidence from stalagmite climate records indicating a major decrease of monsoon rainfall in MSEA during the mid- to late Holocene.Results · Causes Of Monsoon Failure... · Climate Model Simulations
[64]
Greening of the Sahara suppressed ENSO activity during the mid ...
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[65]
An Overview of the Holocene High Sea Level Around the South ...
The mean annual temperature in the Holocene Climatic Optimum in South China and adjacent subtropical East Asia was about 1–2 °C higher than that of the present ...
[66]
Complex spatio-temporal structure of the Holocene Thermal Maximum
Oct 3, 2022 · Here, we analyze a global database of Holocene paleotemperature records to investigate the spatiotemporal structure of the HTM.
[67]
Holocene glacier change in the Silvretta Massif (Austrian Alps ...
Oct 1, 2020 · OcG-15-04 yields a Neoglacial age. Around 5 ka, climate in the European Alps began to change towards cooler and wetter conditions (e.g. ...
[68]
Alpine glacier resilience and Neoglacial fluctuations linked to ...
Nov 18, 2020 · Geological evidence indicates that glaciers in the western United States fluctuated in response to Holocene changes in temperature and precipitation.
[69]
Medieval warmth confirmed at the Norse Eastern Settlement in ...
Feb 6, 2019 · Abundant evidence exists across much of northern Europe for warm conditions during the Medieval Climate Anomaly (MCA, ca. 950–1250 CE) (Solomina ...
[70]
Glacier response to the Little Ice Age during the Neoglacial cooling ...
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The Maunder minimum and the Little Ice Age: an update from recent ...
Dec 4, 2017 · Overall, it is likely that the effect of volcanic eruptions was the largest influence, followed by the drop in solar activity and changes in ...
[72]
Massive volcanic eruptions caused Little Ice Age, froze the Thames
Jan 31, 2012 · A mysterious, centuries-long cool spell, dubbed the Little Ice Age, appears to have been caused by a series of volcanic eruptions and sustained by sea ice.Missing: 1250-1850 CE minima<|control11|><|separator|>
[73]
The Maunder minimum and the Little Ice Age: An update from recent ...
Sep 9, 2025 · The Maunder minimum (MM) was a period of extremely low solar activity from approximately AD 1650 to 1715.
[74]
Trends in CO2 - NOAA Global Monitoring Laboratory
Sep 5, 2025 · The August 2025 CO2 level at Mauna Loa was 425.48 ppm, up from 422.99 ppm in August 2024. Measurements were suspended from Nov 2022 to July ...Missing: pre- industrial
[75]
Trends in CO 2 , CH 4 , N 2 O, SF 6 - Global Monitoring Laboratory
The value of 280 ppm is chosen as representative of pre-industrial air because it is close to the average of CO2 measured and dated with high time ...
[76]
Critical insolation–CO2 relation for diagnosing past and ... - Nature
Jan 13, 2016 · However, moderate anthropogenic cumulative CO2 emissions of 1,000 to 1,500 gigatonnes of carbon will postpone the next glacial inception by at ...Missing: preventing | Show results with:preventing
[77]
IPCC AR6 Working Group 1: Summary for Policymakers
A.1.7 Global mean sea level increased by 0.20 [0.15 to 0.25] m between 1901 and 2018. The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr –1 ...
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[PDF] Fact sheet - Biodiversity
Climate change has altered marine, terrestrial and freshwater ecosystems all around the world (very high confidence). Climate change has caused local ...
[79]
Unexpected future boost of methane possible from Arctic permafrost
Aug 20, 2018 · Due to human-caused warming of the atmosphere from greenhouse gas emissions, a gradual thawing of the permafrost is currently taking place ...
[80]
We now know how much global warming has delayed the next ice age
Feb 27, 2025 · The phasing of obliquity and precession that preceded the Holocene suggests glaciation would be likely to be well underway between 4300 and ...
[81]
https://www.ipcc.ch/report/ar6/wg2/downloads/outreach/IPCC_AR6_WGII_FactSheet_Biodiversity.pdf
[82]
[PDF] A movable trigger: Fossil fuel CO2 and the onset of the next glaciation
May 5, 2005 · Archer, D., and A. Ganopolski (2005), A movable trigger: Fossil fuel CO2 and the onset of the next glaciation, Geochem. Geophys. Geosyst., 6 ...Missing: delay | Show results with:delay
[83]
Reduced-complexity model for the impact of anthropogenic CO2 ...
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