Rapid Climate Shifts Research Articles

Deciphering the spatio-temporal complexity of climate change of the last deglaciation: a model analysis

Abstract. Understanding the sequence of events occuring during the last major glacial to interglacial transition (21 ka BP to 9 ka BP) is a challenging task that has the potential to unveil the mechanisms behind large scale climate changes. Though many studies have focused on the understanding of the complex sequence of rapid climatic change that accompanied or interrupted the deglaciation, few have analysed it in a more theoretical framework with simple forcings. In the following, we address when and where the first significant temperature anomalies appeared when using slow varying forcing of the last deglaciation. We used here coupled transient simulations of the last deglaciation, including ocean, atmosphere and vegetation components to analyse the spatial timing of the deglaciation. To keep the analysis in a simple framework, we did not include freshwater forcings that potentially cause rapid climate shifts during that time period. We aimed to disentangle the direct and subsequent response of the climate system to slow forcing and moreover, the location where those changes are more clearly expressed. In a data – modelling comparison perspective, this could help understand the physically plausible phasing between known forcings and recorded climatic changes. Our analysis of climate variability could also help to distinguish deglacial warming signals from internal climate variability. We thus are able to better pinpoint the onset of local deglaciation, as defined by the first significant local warming and further show that there is a large regional variability associated with it, even with the set of slow forcings used here. In our model, the first significant hemispheric warming occurred simultaneously in the North and in the South and is a direct response to the obliquity forcing.

Coupled deep-water flow and climate variability in the middle Pleistocene North Atlantic

Abrupt changes in the strength of the Atlantic Meridional Overturning Circulation (comprising northward flow of warm water and a cold southward return flow) are implicated in abrupt climate changes in the late Pleistocene. A sensitive place to assess this circulation is in the cold return flow of Deep Western Boundary Currents. Here, in records of flow speed and isotopic composition of surface and bottom waters from a Deep Western Boundary Current location near the northern source of North Atlantic Deep Water, we show both orbital and millennial-scale coupling between deep ocean flow and climate in the middle Pleistocene (0.75–0.87 Ma), when the boundary conditions in terms of the mean state and amplitude of climate change were different from more recent periods. The coupling appears as a phased series of events initiated by reduced vertical density gradients and initial ventilation of deep waters. The occurrence of these events in interglacials during the middle Pleistocene suggests that the millennial-scale climate variability in the North Atlantic was more pronounced at that time than previously thought. This demonstrates that, given the right boundary conditions, rapid climate shifts can also occur during relatively warm climate conditions.

Fire and vegetation shifts in the Americas at the vanguard of Paleoindian migration

Across North and South America, the final millennia of the Pleistocene saw dramatic changes in climate, vegetation, fauna, fire regime, and other local and regional paleo-environmental characteristics. Rapid climate shifts following the Last Glacial Maximum (LGM) exerted a first-order influence, but abrupt post-glacial shifts in vegetation composition, vegetation structure, and fire regime also coincided with human arrival and transformative faunal extinctions in the Americas. We propose a model of post-glacial vegetation change in response to climatic drivers, punctuated by local fire regime shifts in response to megaherbivore-driven fuel changes and anthropogenic ignitions. The abrupt appearance of humans, disappearance of megaherbivores, and resulting changes in New World fire systems were transformative events that should not be dismissed in favor of climate-only interpretations of post-glacial paleo-environmental shifts in the Americas. Fire is a mechanism by which small human populations can have broad impacts, and growing evidence suggests that early anthropogenic influences on regional, even global, paleo-environments should be tested alongside other potential causal mechanisms.

Millennial-scale vegetation dynamics in an estuary at the onset of the Miocene Climate Optimum

Pollen analyses have been proven to possess the possibility to decipher rapid vegetational and climate shifts in Neogene sedimentary records. Herein, a c. 21-kyr-long transgression–regression cycle from the Lower Austrian locality Stetten is analysed in detail to evaluate climatic benchmarks for the early phase of the Middle Miocene Climate Optimum and to estimate the pace of environmental change. Based on the Coexistence Approach, a very clear signal of seasonality can be reconstructed. A warm and wet summer season with c. 204–236 mm precipitation during the wettest month was opposed by a rather dry winter season with precipitation of c. 9–24 mm during the driest month. The mean annual temperature ranged between 15.7 and 20.8 °C, with about 9.6–13.3 °C during the cold season and 24.7–27.9 °C during the warmest month. In contrast, today's climate of this area, with an annual temperature of 9.8 °C and 660 mm rainfall, is characterized by the winter season (mean temperature: −1.4 °C, mean precipitation: 39 mm) and a summer mean temperature of 19.9 °C (mean precipitation: 84 mm). Different modes of environmental shifts shaped the composition of the vegetation. Within few millennia, marshes and salt marshes with abundant Cyperaceae rapidly graded into Taxodiaceae swamps. This quick but gradual process was interrupted by swift marine ingressions which took place on a decadal to centennial scale. The transgression is accompanied by blooms of dinoflagellates and of the green alga Prasinophyta and an increase in Abies and Picea. Afterwards, the retreat of the sea and the progradation of estuarine and wetland settings were a gradual progress again. Despite a clear sedimentological cyclicity, which is related to the 21-kyr precessional forcing, the climate data show little variation. This missing pattern might be due to the buffering of the precessional-related climate signal by the subtropical vegetation. Another explanation could be the method-inherent broad range of climate-parameter estimates that could cover small scale climatic changes.

Glacier reconstruction and mass‐balance modelling as a geomorphic and palaeoclimatic tool

AbstractThe reconstruction of former mountain glaciers has long been used to examine the implications of rapid climate shifts, for example at the last glacial–interglacial transition, and for evaluating asynchronous behaviour of mountain glaciers compared with mid‐latitude ice sheets during the Late Quaternary. Glacier reconstruction has also been used as a source of palaeoclimatic information, based on the recognition of empirical relationships between glaciers and climate. This paper reviews the application and implications of a recently revised method of glacier reconstruction (Carr and Coleman, 2007), based around glaciological principles of mass‐balance. This study examines how this approach can be used to test geomorphological interpretations of former mountain glaciation and also to infer precipitation fields at sites of former glaciation. Sites of Younger Dryas niche and icefield glaciation in the British Isles demonstrate how this method can verify interpretations of marginal glaciation and begin to understand the different behaviour of outlet glaciers within the same environmental regime. Examination of a site of former niche glaciation in Southern Africa demonstrates how glacier reconstruction may be used to infer annual and seasonal precipitation values and strongly supports the idea that winter precipitation in Lesotho and SE South Africa was substantially greater than present‐day values during the last glacial cycle. Copyright © 2010 John Wiley & Sons, Ltd.

The Role of Oceanic Heat Transport and Wind Stress Forcing in Abrupt Millennial-Scale Climate Transitions

Abstract The last glacial period was punctuated by rapid climate shifts, known as Dansgaard–Oeschger events, with strong imprint in the North Atlantic sector suggesting that they were linked with the Atlantic meridional overturning circulation. Here an idealized single-hemisphere three-dimensional ocean–atmosphere–sea ice coupled model is used to explore the possible origin of the instability driving these abrupt events and to provide a plausible explanation for the relative stability of the Holocene. Focusing on the physics of noise-free millennial oscillations under steady external (solar) forcing, it was shown that cold climates become unstable, that is, exhibit abrupt millennial-scale transitions, for significantly lower freshwater fluxes than warm climates, in agreement with previous studies making use of zonally averaged coupled models. This fundamental difference is a direct consequence of the weaker stratification of the glacial ocean, mainly caused by upper-ocean cooling. Using a two-hemisphere configuration of a coupled climate model of intermediate complexity, it is shown that this result is robust to the added presence of a bottom water mass of southern origin. The analysis reveals that under particular conditions, a pronounced interdecadal variability develops during warm interstadials. While the nature of the instability driving the millennial oscillations is identical to that found in ocean models under mixed boundary conditions, these interstadial–interdecadal oscillations share the same characteristics as those previously found in ocean models forced by fixed surface fluxes. The wind stress forcing is shown to profoundly affect both the properties and bifurcation structure of thermohaline millennial oscillations across a wide range of variation of freshwater forcing. In particular, it is shown that the wind stress forcing favors the maintenance of thermally direct meridional overturning circulations during the cold stadial phases of Dansgaard–Oeschger cycles.

Variable winter moisture in the southwestern United States linked to rapid glacial climate shifts

The last glacial period was characterized by large, rapid climate fluctuations. An analysis of a speleothem from New Mexico shows that the coldest conditions over Greenland coincide with increased winter precipitation in the southwestern United States, which can be attributed to a southward displacement of the polar jet stream and the North American storm track. During the last glacial period, the climate of the Northern Hemisphere was characterized by rapid, large-amplitude temperature fluctuations through cycles lasting a few thousand years1,2,3. These fluctuations are apparent in Greenland temperature reconstructions2,3, and corresponding temperature and hydrological variations have been documented throughout the Northern Hemisphere4,5. Here we present a record of precipitation in the southwestern United States from 56,000 to 11,000 yr ago, on the basis of δ18O measurements of speleothem calcite from New Mexico. Our record shows that increased winter precipitation in the southwestern United States is associated with Northern Hemisphere cooling, which we attribute to a southward shift in the polar jet stream, which modulated the position of the winter storm track over North America. On the western side of the Pacific Ocean basin, decreases in summer monsoon precipitation are associated with Northern Hemisphere cooling, due to southward displacement of the intertropical convergence zone4. We conclude that cooling and warming excursions in the Northern Hemisphere lead to concurrent latitudinal displacement of both the intertropical convergence zone and the polar jet stream over the Pacific Ocean. Our data are consistent with modern evidence for a northward shift of the polar jet stream in response to global warming6,7,8, which could lead to increasingly arid conditions in southwestern North America in the future.

Japanese encephalitis-a pathological and clinical perspective.

Japanese encephalitis (JE) is the leading form of viral encephalitis in Asia. It is caused by the JE virus (JEV), which belongs to the family Flaviviridae. JEV is endemic to many parts of Asia, where periodic outbreaks take hundreds of lives. Despite the catastrophes it causes, JE has remained a tropical disease uncommon in the West. With rapid globalization and climatic shift, JEV has started to emerge in areas where the threat was previously unknown. Scientific evidence predicts that JEV will soon become a global pathogen and cause of worldwide pandemics. Although some research documents JEV pathogenesis and drug discovery, worldwide awareness of the need for extensive research to deal with JE is still lacking. This review focuses on the exigency of developing a worldwide effort to acknowledge the prime importance of performing an extensive study of this thus far neglected tropical viral disease. This review also outlines the pathogenesis, the scientific efforts channeled into develop a therapy, and the outlook for a possible future breakthrough addressing this killer disease.

Evidence for Dynamic Climate Change on Sub-106-Year Scales from the Late Paleozoic Glacial Record, Tamworth Belt, New South Wales, Australia

Abstract Models of late Paleozoic ice-age climate dynamics have remained enigmatic, in part because preservation of mid- to Late Carboniferous, ice-proximal, Gondwanan glacial deposits is limited to very few Gondwanan regions. As such, detailed sedimentologic and stratigraphic analysis of six formations comprising the well-preserved, mid-Carboniferous to Lower Permian (Namurian or Serpukhovian to late Sakmarian), terrestrial, glacially influenced record from the Tamworth Belt, New South Wales, Australia, provides a unique opportunity to test existing models of late Paleozoic climate, characterize regional glaciation, and resolve the internal pacing of climate during the late Paleozoic ice age. Facies analysis based on twelve logged vertical sections and lateral facies relationships suggests that sediment accumulated in an eastward-draining, volcaniclastically influenced alluvial fan (facies association FA1), fluvial (FA2), and lacustrine (FA3) landsystem. Evidence for proglacial outwash fan (sandar), glaciofluvial, and glaciolacustrine deposition is preserved in the form of texturally diverse diamictite, outsized clasts in fine-grained facies, and rhythmically laminated sandstone and siltstone. The association of these facies, which is termed herein as “distinctly glacial facies” and is taken as direct evidence of glaciation, does not occur through the stratigraphic extent of formations, suggesting that the Tamworth Belt of New South Wales, Australia, was subject to episodic, mountain/valley-type or outlet-type, temperate to subpolar glaciation during the Carboniferous and Early Permian. Climatic shifts and trends occurred on multiple timescales, termed herein “nested cyclicity.” Alternations between distinctly glacial facies and facies that lack evidence of glacial influence, interpreted to record alternating glacial and nonglacial conditions, occurred on timescales on the order of ~ 106 years. The cited age estimates are based on published estimates of glacial interval durations from the region, which in turn reconcile all available radiogenic isotopic data and biostratigraphic zonations. Facies trends within successions recording glacial intervals are interpreted in terms of glacial advance and retreat, which can be estimated to have occurred on timescales shorter than the duration of glacial intervals (shorter-term, sub-106-yr-order timescales) and may include Milankovitch-band cyclicity. These conclusions support the emerging view that the late Paleozoic was characterized by rapid and dynamic climatic shifts on multiple timescales, rather than as one, long protracted event as portrayed by earlier models of Gondwanan glaciation. Furthermore, this study provides an improved understanding of high-latitude climate dynamics and pacing, which may prove useful in constructing improved global models of late Paleozoic climate.

On the Stochastic Nature of the Rapid Climate Shifts during the Last Ice Age

Abstract The rapid climate shifts observed in the glacial climate are analyzed. The transitions into the warm interstadial states, the onsets, are easily identifiable in the record. The distribution of waiting times between consecutive onsets is well fitted, assuming that the remaining residence time in each state is independent of the past. This implies that it has a simple no-memory exponential waiting time distribution, but with the mean waiting time depending on the climate state. The mean waiting time from one onset to the next is around 2400 yr. The most likely (maximum likelihood) distribution derived solely from the onset sequence is rather insensitive to the mean waiting time in the warm interstadials in the range of 400–1200 yr. When extending the analysis to include the transitions from the warm interstadials to the cold stadials observed with a larger uncertainty, the distributions in the two states are well fitted to exponential distributions, with mean waiting times of around 800 yr in the warm state and around 1600 yr in the cold state. This observation is an important piece in the climate puzzle, because the fact that the climate is a no-memory process indicates that the transitions are noise induced and the mean residence time in one state indicates how stable that climate state is to perturbations. The possibility of a hidden periodic driver is also investigated. The existence of such a driver cannot be ruled out by the relatively sparse data series (containing only 21 onsets). However, because the record is fitted just as well by the much simpler random model, this should be preferred from the point of view of simplicity.

Rapid transitions in the Atlantic thermohaline circulation triggered by global warming and meltwater during the last deglaciation

In a series of sensitivity experiments, using a three‐dimensional ocean general circulation model, rapid climate shifts during the last deglaciation are interpreted in terms of gradual temperature changes and freshwater perturbations, which impact on the Atlantic thermohaline circulation (THC). We show that increasing global temperature leads to a rapid intensification of the THC. The transition to an interglacial THC mode is preconditioned by a decrease of the subsurface temperatures due to an increase in ventilation of the subsurface water in the northern North Atlantic, which enhances the merdional transport of salt to the northern high latitudes and gradually erodes the halocline. This process enables the remaining temperature inversion to overcome the salinity stratification in the northern North Atlantic, which causes a kick start of vigorous convection and a rapid intensification of the Atlantic THC. As a result of the abrupt THC amplification and the deglacial warming and sea ice retreat in the Southern Ocean, enhanced transport of relatively salty surface and intermediate‐depth waters from the Indian Ocean provides an additional source of salt to the North Atlantic, which changes the stability behavior of the THC with respect to freshwater perturbations. A warming‐induced transition from a weak glacial THC to a stronger THC state, with different North Atlantic freshwater hysteresis characteristics, provides a concept that might explain the sequence of events, characterizing the last glacial termination as recorded in proxy data.

Reply to comment by K. Caldeira et al. on “Modern-age buildup of CO2and its effects on seawater acidity and salinity”

Reply to comment by K. Caldeira et al. on “Modern-age buildup of CO₂and its effects on seawater acidity and salinity”

Prehistoric Pinus woodland dynamics in an upland landscape in northern Scotland: the roles of climate change and human impact

Pollen, microscopic charcoal, palaeohydrolog- ical and dendrochronological analyses are applied to a radiocarbon and tephrochronologically dated mid Holocene (ca. 8500-3000 cal B.P.) peat sequence with abundant fossil Pinus (pine) wood. The Pinus populations on peat fluctuated considerably over the period in question. Colo- nisation by Pinus from ca. 7900-7600 cal B.P. appears to have had no specific environmental trigger; it was probably determined by the rate of migration from particular popu- lations. The second phase, at ca. 5000-4400 cal B.P., was facilitated by anthropogenic interference that reduced competition from other trees. The pollen record shows two Pinus declines. The first at ca. 6200-5500 cal B.P. was caused by a series of rapid and frequent climatic shifts. The second, the so-called pine decline, was very gradual (ca. 4200-3300 cal B.P.) at Loch Farlary and may not have been related to climate change as is often supposed. Low intensity but sustained grazing pressures were more important. Throughout the mid Holocene, the frequency and intensity of burning in these open Pinus-Calluna woods were probably highly sensitive to hydrological (climatic) change. Axe marks on several trees are related to the mid to late Bronze Age, i.e., long after the trees had died.

Evidence for a Rapid Global Climate Shift across the Late 1960s

Abstract It is shown that a number of important characteristics of the global atmospheric circulation and climate changed in a near-monotonic fashion over the decade, or less, centered on the late 1960s. These changes were largest or commonest in tropical regions, the Southern Hemisphere, and the Atlantic sector of the Northern Hemisphere. Some, such as the decrease in rainfall in the African Sahel, are well known. Others appear to be new, but their combined extent is global and dynamical linkages between them are evident. The list of affected variables includes patterns of SST; tropical rainfall in the African Sahel and Sudan, the Amazon basin, and northeast Brazil; pressure and SST in the tropical North Atlantic and the west and central Pacific; various branches of the southern Hadley circulation and the southern subtropical jet stream; the summer North Atlantic Oscillation; south Greenland temperature; the Southern Hemisphere storm track; and, quite likely, the Antarctic sea ice boundary. These changes are often strongest in the June–August season; changes are also seen in December–February but are generally smaller. In Greenland, annual mean temperature seems to be affected strongly, reflecting similar changes in SST throughout the year in the higher latitudes of the North Atlantic. Possible causes for these coordinated changes are briefly evaluated. The most likely candidates appear to be a likely reduction in the northward oceanic heat flux associated with the North Atlantic thermohaline circulation in the 1950s to 1970s, which was nearly in phase with a rapid increase in anthropogenic aerosol emissions during the 1950s and 1960s, particularly over Europe and North America.

RESOLuTION - Rapid climatic and environmental shifts during Oxygen Isotope Stages 2 and 3 - linking highresolution terrestrial, ice core and marine archives

RESOLuTION – Rapid climatic and environmental shifts during Oxygen Isotope Stages 2 and 3 – linking high-resolution terrestrial, ice core and marine archives

Paleomonsoon precipitation deduced from a sediment core from the equatorial Indian Ocean

Rapid shifts in past climate recorded in polar ice sheets have elicited various explanations relating to either thermohaline circulation changes by ice-rafting or natural greenhouse gas concentrations modulated by climatic conditions in the tropics. To compare the tropical paleoclimate record with the polar record, one must choose sediment cores from highly productive ocean regions. Necessarily, such regions reflect the wind records in the tropics, because high productivity is associated with upwelling driven by winds. Comparing tropical precipitation records with high-latitude records is, however, a more difficult task because sediments recording paleoprecipitation usually have low sedimentation rates, and offer coarser resolution relative to polar ice cores. Here, we present δ 18O data of three planktonic species of Foraminifera (a proxy for precipitation) from such a sediment core, spanning the past 35 ka for the equatorial Indian Ocean, which falls under the southwest monsoon (SWM) realm. Results show that minimum SWM precipitation occurred at the Last Glacial Maximum, with a subsequent increase at Termination IA. During the Holocene, SWM precipitation intensified uniformly up to the core top (∼2.2 ka b.p.), as revealed by generally decreasing δ 18O values. Variations in precipitation are consistent with climate changes recorded in polar ice sheets. Although the different resolutions of the two records preclude a rigorous comparison, abrupt cooling/warming events appear to be accompanied by sudden reduction/enhancement in (SWM) rainfall. Thus, mechanisms with time scales much shorter than a millennium, such as natural greenhouse warming (e.g., CH4 concentration), controlled by emissions from the tropics, could have played a major role in high-latitude climate change.

Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model

Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle.

Late-Quaternary lowstands of lake Bosumtwi, Ghana: evidence from high-resolution seismic-reflection and sediment-core data

Results from the first high-resolution, single-channel seismic-reflection survey of tropical Lake Bosumtwi, Ghana, and sedimentological data from a 14C-dated sediment piston core were used to revise and extend the basin's late-Quaternary lake level history. We report four seismic sequence boundaries and an exposure surface from a sediment core, which are interpreted as erosional surfaces formed at times of drastic low lake level. The youngest erosional surface occurs as much as 31 m below present lake level (bpll) and up to 0.7 m below the present sediment–water interface. This most recent unconformity observed in the seismic data is interpreted to be coeval with the basin-wide late-Holocene dry period between 0.5 and 1 cal ky BP (calendar years before present). Another exposure surface observed in a sediment core is based on an abrupt contact separating low density, wet, clay rich sediments from underlying high density, compact, silt-rich and rootlet-rich sediments, and is interpreted to have developed prior to 16.8 cal ky BP when the lake was ∼60 m bpll. Three older, erosional surfaces occur at depths of ∼92±3, 102±3, and 107±4 m bpll, suggesting numerous lowstands in Lake Bosumtwi during the late-Pleistocene. By extrapolation of average sedimentation rates (0.41 m/ky) from the upper ∼10.5 m of sediment, we estimate the ages of these older lowstands to be ∼65, ∼86, ∼108 cal ky BP. The lowstands of Lake Bosumtwi evidenced from the seismic and sediment core data are interpreted as a response to increased aridity in this part of the equatorial tropics and may correlate to other observed continent-wide shifts in African climate over the past 100 ky, and possibly to rapid climatic shifts observed at high latitudes. Determining the precise timing of these lowstands will ultimately reveal much about the drought dynamics of tropical and subtropical Africa.

On the rheology of till

AbstractThe deformation of subglacial till is instrumental in causing certain glacier surges, the motion of rapid ice streams in ice sheets, and ice-sheet surges which are associated with Heinrich events, and consequent rapid climatic shifts, during the last ice age. It may also be the means whereby drumlins are formed, and these in turn may act as a brake on large-scale ice flow. It is therefore important in building models to understand the rate at which till deforms, and how this controls the basal ice velocity. In recent years, two paradigms have emerged. On the one hand, theoreticians have tended to use a viscous rheology, though this lacks quantitative support. On the other hand, field and laboratory studies suggest that till behaves plastically. In this paper I will examine some of the dynamic consequences of this latter assumption, and show how the dichotomy between viscous and plastic may be less clear-cut than previously thought.

The Fate of Clades in a World of Recurrent Climatic Change: Milankovitch Oscillations and Evolution

▪ Abstract Variations in Earth's orbit with periods of 10–100 thousand years (kyr) (Milankovitch oscillations) have led to recurrent and rapid climatic shifts throughout Earth's history. These cause changes in the geographical distributions of clades, which we term orbitally forced range dynamics (ORD). The magnitude of ORD varies geographically, e.g., with latitude. Climatic shifts cause extinction, splitting, and merging of gene pools and clades. They select among individuals and clades for traits enhancing the ability to survive in situ and to establish new populations. There is also nonadaptive sorting caused by the large geographical variation in ORD, as only gene pools that are in the right place when climate shifts survive. ORD lead to sorting at many levels of genealogic inclusiveness. Clades that have survived climatic shifts during at least one entire period of the longest significant Milankovitch oscillations (100 kyr), we name β-clades. The products of more recent cladogenesis are α-clades, which are always nested within a β-clade. We conclude that ORD may promote α-clade formation but curb rates of β-clade formation. In areas with little ORD, where gene pools persist without going extinct or merging, clade splits and divergence may accumulate leading to high rates of β-clade formation and β-anagenesis (evolutionary change persisting >100 kyr). High ORD should lead to low numbers of β-clades, β-clades with low levels of spatial genetic divergence, little geographical subdivision and large ranges, organisms with high vagility and low specialization, high proportions of β-clades formed by polyploidization, and little β-anagenesis. We predict global and interregional geographic patterns in these variables caused by differential ORD. Thus, ORD potentially explains a wide array of patterns, suggesting ORD as a fundamental factor in evolution. The vulnerability of biotas to many human activities should vary with the magnitude of ORD.