
The 100,000-year problem (also 100 ky problem or 100 ka problem) of the
Milankovitch theory of
orbital forcing
Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the Earth's orbit around the Sun (see Milankovitch cycles). These orbital changes modify the total amount of sunlight reaching the Earth by up to ...
refers to a discrepancy between the reconstructed
geologic temperature record and the reconstructed amount of incoming solar radiation, or
insolation
Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre ...
over the past 800,000 years. Due to variations in the Earth's orbit, the amount of insolation varies with periods of around 21,000, 40,000, 100,000, and 400,000 years. Variations in the amount of incident solar energy drive changes in the
climate
Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteoro ...
of the Earth, and are recognised as a key factor in the timing of initiation and termination of
glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
s.
While there is a Milankovitch cycle in the range of 100,000 years, related to Earth's
orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...
, its contribution to variation in insolation is much smaller than those of
precession
Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In o ...
and
obliquity
In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbital ...
. The 100,000-year problem refers to the lack of an obvious explanation for the periodicity of
ice age
An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
s at roughly 100,000 years for the past million years, but not before, when the dominant periodicity corresponded to 41,000 years.
The unexplained transition between the two periodicity regimes is known as the
Mid-Pleistocene Transition
The Mid-Pleistocene Transition (MPT), also known as the Mid-Pleistocene Revolution (MPR), is a fundamental change in the behaviour of glacial cycles during the Quaternary glaciations. The transition lasted around 550,000 years, from 1.25 million ...
, dated to some 800,000 years ago.
The related 400,000-year problem refers to the absence of a 400,000-year periodicity due to
orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...
in the geological temperature record over the past 1.2 million years.
The transition in periodicity from 41,000 years to 100,000 years can now be reproduced in numerical simulations that include a decreasing trend in
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
and glacially induced removal of
regolith
Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...
, as explained in more detail in the article ''
Mid-Pleistocene Transition
The Mid-Pleistocene Transition (MPT), also known as the Mid-Pleistocene Revolution (MPR), is a fundamental change in the behaviour of glacial cycles during the Quaternary glaciations. The transition lasted around 550,000 years, from 1.25 million ...
''.
Recognition of the 100,000-year cycle
The
geologic temperature record can be
reconstructed from sedimentary evidence. Perhaps the most useful
paleotemperature indicator of past climate is the
fractionation
Fractionation is a separation process in which a certain quantity of a mixture (of gasses, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities (fractions) in which t ...
of
oxygen isotopes, denoted . This fractionation is controlled mainly by the amount of water locked up in ice and the absolute temperature of the planet and has allowed a timescale of
marine isotope stage
Marine isotope stages (MIS), marine oxygen-isotope stages, or oxygen isotope stages (OIS), are alternating warm and cool periods in the Earth's paleoclimate, deduced from Oxygen isotope ratio cycle, oxygen isotope data derived from deep sea core ...
s to be constructed.
By the late 1990s, records of air (in the
Vostok
Vostok () refers to east in Russian but may also refer to:
Spaceflight
* Vostok programme, Soviet human spaceflight project
* Vostok (spacecraft), a type of spacecraft built by the Soviet Union
* Vostok (rocket family), family of rockets derived ...
ice core) and marine
sediments
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
were available and were compared with estimates of
insolation
Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument.
Solar irradiance is measured in watts per square metre ...
, which should affect both temperature and ice volume. As described by
Shackleton (2000), the deep-sea sediment record of "is dominated by a 100,000-year cyclicity that is universally interpreted as the main ice-age rhythm". Shackleton (2000) adjusted the time scale of the Vostok ice core record to fit the assumed
orbital forcing
Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the Earth's orbit around the Sun (see Milankovitch cycles). These orbital changes modify the total amount of sunlight reaching the Earth by up to ...
and used spectral analysis to identify and subtract the component of the record that in this interpretation could be attributed to a linear (directly proportional) response to the orbital forcing. The residual signal (the remainder), when compared with the residual from a similarly retuned marine core isotope record, was used to estimate the proportion of the signal that was attributable to ice volume, with the rest (having attempted to allow for the
Dole effect) being attributed to temperature changes in the deep water.
The 100,000-year component of ice volume variation was found to match sea level records based on coral age determinations, and to lag orbital eccentricity by several thousand years, as would be expected if orbital eccentricity were the pacing mechanism. Strong non-linear "jumps" in the record appear at
deglaciation
Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice shee ...
s, although the 100,000-year periodicity was not the strongest periodicity in this "pure" ice volume record.
The separate deep sea temperature record was found to vary directly in phase with orbital eccentricity, as did the Antarctic temperature and CO
2; so eccentricity appears to exert a geologically immediate effect on air temperatures, deep-sea temperatures, and atmospheric carbon dioxide concentrations. Shackleton (2000) concluded: "The effect of orbital eccentricity probably enters the paleoclimatic record through an influence on the concentration of atmospheric CO
2".
Elkibbi and Rial (2001) identified the 100 ka cycle as one of five main challenges met by the
Milankovitch model of
orbital forcing
Orbital forcing is the effect on climate of slow changes in the tilt of the Earth's axis and shape of the Earth's orbit around the Sun (see Milankovitch cycles). These orbital changes modify the total amount of sunlight reaching the Earth by up to ...
of the ice ages.
Hypotheses to explain the problem
As the 100,000-year periodicity only dominates the climate of the past million years, there is insufficient information to separate the component frequencies of eccentricity using spectral analysis, making the reliable detection of significant longer-term trends more difficult, although the spectral analysis of much longer palaeoclimate records, such as the Lisiecki and Raymo stack of marine cores and James Zachos' composite isotopic record, helps to put the last million years in a longer-term context. Hence there is still no clear proof of the mechanism responsible for the 100 ka periodicity—but there are several credible hypotheses.
Climatic resonance
The mechanism may be internal to the Earth system. The Earth's climate system may have a natural
resonance frequency
Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...
of 100 ka; that is to say, feedback processes within the climate automatically produce a 100 ka effect, much as a bell naturally rings at a certain pitch.
Opponents to this claim point out that the resonance would have to have developed 1 million years ago, as a 100 ka periodicity was weak to non-existent for the preceding 2 million years. This is feasible—
continental drift
Continental drift is a highly supported scientific theory, originating in the early 20th century, that Earth's continents move or drift relative to each other over geologic time. The theory of continental drift has since been validated and inc ...
and
sea floor spreading
Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
History of study
Earlier theories by Alfred Wegener ...
rate change have been postulated as possible causes of such a change.
Free oscillations of components of the Earth system have been considered as a cause,
but too few Earth systems have thermal inertia on a thousand-year timescale for any long-term changes to accumulate. The most common hypothesis looks to the Northern Hemisphere ice sheets, which might expand through a few shorter cycles until large enough to undergo a sudden collapse. The 100,000-year problem has been scrutinized by José A. Rial, Jeseung Oh and Elizabeth Reischmann who find that synchronization between the climate system's natural frequencies and the eccentricity forcing started the 100 ky ice ages of the late Pleistocene and explain their large amplitude.
Orbital inclination
Orbital inclination
Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.
For a satellite orbiting the Earth ...
has a 100 ka periodicity, while
eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-Centre (geometry), center, in geometry
* Eccentricity (g ...
's 95 and 125ka periods could inter-react to give a 108ka effect. While it is possible that the less significant, and originally overlooked, inclination variability has a deep effect on climate,
the eccentricity only modifies insolation by a small amount: 1–2% of the shift caused by the 21,000-year precession and 41,000-year obliquity cycles. Such a big impact from inclination would therefore be disproportionate in comparison to other cycles.
One possible mechanism suggested to account for this was the passage of Earth through regions of cosmic dust. Our eccentric orbit would take us through dusty clouds in space, which would act to occlude some of the incoming radiation, shadowing the Earth.
In such a scenario, the abundance of the isotope
3He,
produced by
solar ray
''Solar Ray'' (stylized and subtitled as ''SOLAR RAY Hirasawa best recycling album Recycled by P-MODEL kernel'') is a 2001 remix album by Susumu Hirasawa. It is the centerpiece of "Hirasawa Energy Works", a project to produce music in an ecologica ...
s splitting gases in the upper atmosphere, would be expected to decrease—and initial investigations did indeed find such a drop in
3He abundance.
Others have argued possible effects from the dust entering the atmosphere itself, for example by increasing cloud cover (on 9 July and 9 January, when the Earth passes through the invariable plane,
mesospheric cloud increases).
Therefore, the 100 ka eccentricity cycle can act as a "pacemaker" to the system, amplifying the effect of precession and obliquity cycles at key moments, with its perturbation.
Precession cycles
A similar suggestion holds the 21,636-year
precession cycles solely responsible. Ice ages are characterized by the slow buildup of ice volume, followed by relatively swift melting phases. It is possible that ice built up over several precession cycles, only melting after four or five such cycles.
Dust and albedo
It has been suggested that ice-sheet albedo and dust are responsible. The high albedo of northern ice sheets will resist climatic warming from Milankovitch maxima unless they are covered in dust. Dust episodes occur just before each interglacial warming period, and it is claimed that the resulting reduced albedo of northern ice sheets assists in interglacial warming. Dust episodes are said to be caused by low atmospheric creating -deserts in northern China upland areas, with the resulting dust creating the Loess Plateau and coating the northern ice sheets.
Solar luminosity fluctuation
A mechanism that may account for periodic fluctuations in solar luminosity has also been proposed as an explanation. Diffusion waves occurring within the Sun can be modeled in such a way that they explain the observed climatic shifts on Earth.
Land vs. oceanic photosynthesis
The
Dole effect describes trends in arising from trends in the relative importance of land-dwelling and oceanic
photosynthesizers. Such a variation is a plausible cause of the phenomenon.
Ongoing research
The recovery of higher-
resolution ice core
An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier
A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier ...
s spanning more of the past 1,000,000 years by the ongoing
EPICA project may help shed more light on the matter. A new, high-precision dating method developed by the team
allows better
correlation
In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statistics ...
of the various factors involved and puts the ice core chronologies on a stronger temporal footing, endorsing the traditional
Milankovitch hypothesis, that climate variations are controlled by insolation in the northern hemisphere. The new chronology is inconsistent with the "inclination" theory of the 100,000-year cycle. The establishment of leads and lags against different orbital forcing components with this method—which uses the direct insolation control over nitrogen-oxygen ratios in ice core bubbles—is in principle a great improvement in the temporal resolution of these records and another significant validation of the Milankovitch hypothesis. An international climate modelling exercise (Abe-ouchi ''et al.'', Nature, 2013
) demonstrated that climate models can replicate the 100,000-year cyclicity given the orbital forcing and carbon dioxide levels of the late Pleistocene. The isostatic history of ice sheets was implicated in mediating the 100,000-year response to the orbital forcing. Larger ice sheets are lower in elevation because they depress the continental crust upon which they sit, and are therefore more vulnerable to melting.
See also
*
Brunhes–Matuyama reversal
The Brunhes–Matuyama reversal, named after Bernard Brunhes and Motonori Matuyama, was a geologic event, approximately 781,000 years ago, when the Earth's magnetic field last underwent reversal. Estimations vary as to the abruptness of the reve ...
*
Chibanian
The Chibanian, more widely known as the Middle Pleistocene (its previous informal name), is an Age (geology), age in the international geologic timescale or a Stage (stratigraphy), stage in chronostratigraphy, being a division of the Pleistocen ...
*
Milankovitch cycles
Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term was coined and named after the Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he pr ...
*
Paleoclimatology
Paleoclimatology ( British spelling, palaeoclimatology) is the scientific study of climates predating the invention of meteorological instruments, when no direct measurement data were available. As instrumental records only span a tiny part of ...
*
Timeline of glaciation
There have been five or six major ice ages in the history of Earth over the past 3 billion years.
The Late Cenozoic Ice Age began 34 million years ago, its latest phase being the Quaternary glaciation, in progress since 2.58 million years ago. ...
Notes
References
{{DEFAULTSORT:100, 000-Year Problem
Ice ages
History of climate variability and change