Archives par mot-clé : Milankovitch

climate and geology

Elegantly modeling Earth’s abrupt glacial transitions

by American Institute of Physics, Mar 7, 2023 in ScienceDaily

Proxy data — indirect records of the Earth’s climate found in unlikely places like coral, pollen, trees, and sediments — show interesting oscillations approximately every 100,000 years starting about 1 million years ago. Strong changes in global ice volume, sea level, carbon dioxide concentration, and surface temperature indicate cycles of a long, slow transition to a glacial period and an abrupt switch to a warm and short interglacial period.

Milutin Milankovitch hypothesized that the timing of these cycles was controlled by the orbital parameters of the Earth, including the shape of its path around the sun and the tilt of the planet. A slightly closer orbit or more tilted planet could create a small increase in solar radiation and a feedback loop that leads to massive changes in climate. This idea suggests that there may be some predictability in the climate, a notoriously complex system.

In Chaos, by AIP Publishing, Stefano Pierini of Parthenope University of Naples proposed a new paradigm to simplify the verification of the Milankovitch hypothesis.

“The main motivation behind this study was the wish to characterize and illustrate the Milankovitch hypothesis in a simple, elegant, and intuitive way,” Pierini said.

Many models suggest that Milankovitch is correct; however, such methods are often detailed and study specific. They incorporate climate feedback loops — for example, increased ice cover reflects more radiation back into space, leading to further cooling and more ice cover — as threshold crossing rules. This means that an abrupt jump in climate only occurs once a parameter reaches a given tipping point.

Pierini’s “deterministic excitation paradigm” combines the physics concepts of relaxation oscillation and excitability to link Earth’s orbital parameters and the glacial cycles in a more generic way. The relaxation oscillation component describes how the climate slowly returns to its original glacier state after it is disturbed. At that point, the excitability piece of the model captures the external orbital changes and triggers the next glacial cycle.

By using his own threshold crossing rules and adopting a classical energy-balance model, Pierini obtained correct and robust timing of the most recent glacial cycles.`

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climate and geology, climate-debate

Nature Unbound I: The Glacial Cycle

by Javier, Oct 24, 2016 in ClimateEtc.

Insights into the debate on whether the Holocene will be long or short.

Summary: Milankovitch Theory on the effects of Earth’s orbital variations on insolation remains the most popular explanation for the glacial cycle since the early 1970’s. According to its defenders, the main determinant of a glacial period termination is high 65° N summer insolation, and a 100 kyr cycle in eccentricity induces a non-linear response that determines the pacing of interglacials. Based on this theory some authors propose that the current interglacial is going to be a very long one due to a favorable evolution of 65° N summer insolation. Available evidence, however, supports that the pacing of interglacials is determined by obliquity, that the 100 kyr spacing of interglacials is not real, and that the orbital configuration and thermal evolution of the Holocene does not significantly depart from the average interglacial of the past 800,000 years, so there is no orbital support for a long Holocene.

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climate and geology

The inter-glacial cycle is not a 100,000-year cycle, it is a shorter cycle with missing beats

by M.O. Jonas, 2022, WorldJ.Adv.ResReviews

Review Article
World Journal of Advanced Research and Reviews, 2022, 13(03), 388–392
Article DOI: 10.30574/wjarr.2022.13.3.0259
Publication history:
Received on 18 February 2022; revised on 20 March 2022; accepted on 22 March 2022
Abstract:
The “100,000-year problem” refers to an apparent unexplained change in the frequency of inter-glacial periods which occurred about a million years ago. Before that, inter-glacial periods seemed to occur about every 41,000 years, in line with the obliquity Milankovich cycle. But after that, they seemed to occur about every 100,000 years, in line with the orbital inclination Milankovich cycle. Examination of the data shows that there never was a 41,000-year cycle, and that there is no 100,000-year cycle, but that the most influential cycle is the approx 21,000-year precession cycle which is the major factor in the cycles of insolation at higher latitudes. Insolation at 65N is generally regarded as the most significant of these. Inspection of the data shows that every glacial termination (start of an inter-glacial period) began at a time when insolation at 65N increased from a low point in its cycle. That not every such cycle triggered a new inter-glacial period underlines the chaotic non-linear nature of Earth’s climate. Until about a million years ago, this cycle occasionally “missed a beat”, making the inter-glacial frequency average about 41,000 years. After that, the cycle started missing more “beats”, making the inter-glacial frequency average about 100,000 years. There never was an actual 41,000-year or 100,000-year inter-glacial cycle.
Keywords:
Climate; Glacial Termination; Inter-Glacial; Milankovich Cycle; Non-Linear; Precession
Full text article in PDF:
biology+acidification, climate-debate

Scientists discover link between climate change and biological evolution of phytoplankton

by Rutgers University, Dec 2, 2021 in WUWT

New Brunswick, N.J. (Dec. 1, 2021) – Using artificial intelligence techniques, an international team that included Rutgers-New Brunswick researchers have traced the evolution of coccolithophores, an ocean-dwelling phytoplankton group, over 2.8 million years.

Their findings, published this week in the journal Nature, reveal new evidence that evolutionary cycles in a marine phytoplankton group are related to changes in tropical seasonality, shedding light on the link between biological evolution and climate change.

Coccolithophores are abundant single-celled organisms that surround themselves with microscopic plates made of calcium carbonate, called coccoliths. Due to their photosynthetic activity, mineral production and widespread abundance throughout the world’s oceans, coccolithophores play an important role in the carbon cycle.

Scientists have long thought that climate changes’ effects on plants, animals and other organisms occur in cycles, which are reversed when each cycle is completed, thus erasing any small evolutionary changes during each cycle. In contrast, evolutionary changes, as known from the fossil record, are non-cyclic trends that occur over millions of years.

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