scholarly journals Abrupt climate changes and the astronomical theory

2021 ◽  
Author(s):  
Denis-Didier Rousseau ◽  
Witold Bagniewski ◽  
Michael Ghil
Keyword(s):  
Northern Hemisphere ◽  
Climate Changes ◽  
Ice Sheets ◽  
Climate System ◽  
Time Interval ◽  
Short Time Interval ◽  
The Past ◽  
Major Player ◽  
Astronomical Theory ◽  
Ird Events

Abstract. Abrupt climate changes constitute a relatively new field of research, which addresses variations occurring in a relatively short time interval of tens to a hundred years. Such time scales do not correspond to the tens or hundreds of thousands of years that the astronomical theory of climate addresses. The latter theory involves parameters that are external to the climate system and whose multi-periodic variations are reliably known and almost constant for a large extent of Earth history. Abrupt changes, conversely, appear to involve fast processes that are internal to the climate system; these processes varied considerably during the past 2.6 Myr, and yielded more irregular fluctuations. In this paper, we re-examine the main climate variations determined from the U1308 North Atlantic marine record, which yields a detailed calving history of the Northern Hemisphere ice sheets over the past 3.2 Myr. The magnitude and periodicity of the ice-rafted debris (IRD) events observed in the U1308 record allow one to determine the timing of several abrupt climate changes, the larger ones corresponding to the massive iceberg discharges labeled Heinrich events (HEs). In parallel, abrupt warmings, called Dansgaard-Oeschger (DO) events, have been identified in the Greenland records of the last glaciation cycle. Combining the HE and DO observations, we study a complex mechanism that may lead to the observed millennial-scale variability corresponding to the abrupt climate changes of last 0.9 Myr. This mechanism relies on amended Bond cycles, which group DO events and the associated Greenland stadials into a trend of increased cooling, with IRD events embedded into every stadial, the latest of these being an HE. These Bond cycles may have occurred during the last 0.9 Ma when Northern Hemisphere ice sheets reached their maximum extent and volume, thus becoming a major player in this time interval’s climate dynamics. Since the waxing and waning of ice sheets during the Quaternary period are orbitally paced, we conclude that the abrupt climate changes observed during the Mid and Upper Pleistocene are therewith indirectly linked to the astronomical theory of climate.

scholarly journals Mid-Pleistocene transition in glacial cycles explained by declining CO2and regolith removal

2019 ◽  
Vol 5 (4) ◽  
pp. eaav7337 ◽  
Author(s):  
M. Willeit ◽  
A. Ganopolski ◽  
R. Calov ◽  
V. Brovkin
Keyword(s):  
Climate Variability ◽  
Carbon Cycle ◽  
Northern Hemisphere ◽  
Seasonal Variations ◽  
Ice Sheets ◽  
Glacial Cycles ◽  
Solar Insolation ◽  
The Past ◽  
Transient Simulations

Variations in Earth’s orbit pace the glacial-interglacial cycles of the Quaternary, but the mechanisms that transform regional and seasonal variations in solar insolation into glacial-interglacial cycles are still elusive. Here, we present transient simulations of coevolution of climate, ice sheets, and carbon cycle over the past 3 million years. We show that a gradual lowering of atmospheric CO2and regolith removal are essential to reproduce the evolution of climate variability over the Quaternary. The long-term CO2decrease leads to the initiation of Northern Hemisphere glaciation and an increase in the amplitude of glacial-interglacial variations, while the combined effect of CO2decline and regolith removal controls the timing of the transition from a 41,000- to 100,000-year world. Our results suggest that the current CO2concentration is unprecedented over the past 3 million years and that global temperature never exceeded the preindustrial value by more than 2°C during the Quaternary.

scholarly journals Forcing of late Pleistocene ice volume by spatially variable insolation

2018 ◽  
Author(s):  
Kristian Agasøster Haaga ◽  
Jo Brendryen ◽  
David Diego ◽  
Bjarte Hannisdal
Keyword(s):  
Northern Hemisphere ◽  
Late Pleistocene ◽  
Climate Changes ◽  
Ice Sheets ◽  
Reconstruction Method ◽  
Ice Volume ◽  
Model Free ◽  
Global Ice Volume ◽  
Quaternary Climate ◽  
Insolation Forcing

Changes in Earth's orbit have been dubbed a pacemaker of Quaternary glacial-interglacial climate variability. However, the significance of latitudinally varying insolation as a dynamical forcing of late Pleistocene climate changes remains unclear. Here we use a model-free state-space reconstruction method to quantify the strength of the dynamical influence of locally varying summer energy on global ice volume, with orbitally independent age assignments. Our empirical approach suggests that integrated summer insolation at specific latitudes was a significant driver of ice volume during the past 800,000 years. Summer energy impact on ice volume is detected in a continuous latitudinal band at 50-90°N, consistent with the role of summer melting of Northern Hemisphere ice sheets predicted by Milankovitch theory. Insolation forcing at southern mid-latitudes strongly covaries with the canonical Milankovitch forcing, and coincides with the subtropical front and the mid-latitude westerlies, the modulation of which has been implicated in Quaternary climate changes. In contrast, the dynamics of summer energy forcing in the Northern Hemisphere south of the extent of ice sheets is different, possibly capturing ice volume sensitivity to latitudinal insolation gradients. Our results show that the importance of external forcing on late Pleistocene ice ages cannot be fully accounted for by a unique insolation forcing time series. The global ice volume response to spatially variable summer energy encompasses a range of physical processes that operate at different times of the year, including forcing signals with a wide spectrum of obliquity-to-precession frequency ratios.

scholarly journals Cenozoic global ice-volume and temperature simulations with 1-D ice-sheet models forced by benthic δ18O records

2010 ◽  
Vol 51 (55) ◽  
pp. 23-33 ◽  
Author(s):  
B. De Boer ◽  
R.S.W. van de Wal ◽  
R. Bintanja ◽  
L.J. Lourens ◽  
E. Tuenter
Keyword(s):  
Sea Level ◽  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Surface Air Temperature ◽  
Transient Behaviour ◽  
Ice Volume ◽  
The Past ◽  
Global Ice Volume ◽  
Hemisphere Surface

AbstractVariations in global ice volume and temperature over the Cenozoic era have been investigated with a set of one-dimensional (1-D) ice-sheet models. Simulations include three ice sheets representing glaciation in the Northern Hemisphere, i.e. in Eurasia, North America and Greenland, and two separate ice sheets for Antarctic glaciation. The continental mean Northern Hemisphere surface-air temperature has been derived through an inverse procedure from observed benthic δ18O records. These data have yielded a mutually consistent and continuous record of temperature, global ice volume and benthic δ18O over the past 35 Ma. The simple 1-D model shows good agreement with a comprehensive 3-D ice-sheet model for the past 3 Ma. On average, differences are only 1.0˚C for temperature and 6.2 m for sea level. Most notably, over the 35 Ma period, the reconstructed ice volume–temperature sensitivity shows a transition from a climate controlled by Southern Hemisphere ice sheets to one controlled by Northern Hemisphere ice sheets. Although the transient behaviour is important, equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric, providing limited evidence for hysteresis. Furthermore, the results show a good comparison with other simulations of Antarctic ice volume and observed sea level.

scholarly journals Cumulated insolation: a simple explanation of Milankovitch's forcing on climate changes

2013 ◽  
Vol 9 (5) ◽  
pp. 5553-5568 ◽  
Author(s):  
F. Marra
Keyword(s):  
Northern Hemisphere ◽  
Oxygen Isotopes ◽  
Climate Changes ◽  
Ice Sheets ◽  
Simple Explanation ◽  
Glacial Cycle ◽  
Conditioning Factor ◽  
Summer Insolation ◽  
Satisfactory Answer

Abstract. The occurrence of the sudden melting of the ice sheets during the glacial terminations is explained in this paper as the consequence of the combined role of the minima and the maxima of mean summer insolation on the Northern Hemisphere, providing a new contribution to understand the mechanisms ruling glacial forcing. Indeed, no satisfactory answer has been provided so far to the question why one specific maximum, after a series of consecutive maxima of insolation, has the potentiality to trigger a deglaciation. The explanation proposed in this paper accounts for a pre-conditioning factor, represented by "mild" (warmer) minimum, followed by a sufficiently warm maximum as the conditions that cause the end of a glacial cycle. These conditions are realized whenever the sum of the values of each consecutive minima and maxima ("cumulated insolation") on the curve of mean summer insolation at 65° N exceeds 742 Watt m−2. The comparison of the succession of these cumulated insolation values with the astronomically tuned Oxygen isotopes record provides a satisfactory match with the occurrence of all the glacial terminations in the last 800 ka.

scholarly journals The penultimate deglaciation: protocol for PMIP4 transient numerical simulations between 140 and 127 ka

2018 ◽  
Author(s):  
Laurie Menviel ◽  
Emilie Capron ◽  
Aline Govin ◽  
Andrea Dutton ◽  
Lev Tarasov ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Working Group ◽  
Ice Sheets ◽  
Climate System ◽  
Time Interval ◽  
Last Deglaciation ◽  
Last Interglacial ◽  
Transient Simulations ◽  
The Last Deglaciation ◽  
Continental Ice Sheets

Abstract. The penultimate deglaciation (~ 138–128 thousand years before present, hereafter ka) is the transition from the penultimate glacial maximum to the Last Interglacial (LIG, ~ 129–116 ka). The LIG stands out as one of the warmest interglacials of the last 800 ka, with high-latitude temperature warmer than today and global sea level likely higher by at least 6 meters. The LIG therefore receives ever-growing attention, in particular to identify mechanisms and feedbacks responsible for such regional warmth that is comparable to that expected before 2100. Considering the transient nature of the Earth system, the LIG climate and ice-sheets evolution were certainly influenced by the changes occurring during the penultimate deglaciation. It is thus important to investigate the climate and environmental response to the large changes in boundary conditions (i.e. orbital configuration, atmospheric greenhouse gas concentrations, ice sheet geometry) occurring during this time interval. A deglaciation working group has recently been set up as part of the Paleoclimate Modelling Intercomparison Project (PMIP) phase 4, with a protocol to perform transient simulations of the last deglaciation (19–11 ka). Similar to the last deglaciation, the disintegration of continental ice-sheets during the penultimate deglaciation led to significant changes in the oceanic circulation during Heinrich Stadial 11 (~ 136–129 ka). However, the two deglaciations bear significant differences in magnitude and temporal evolution of climate and environmental changes. Here, as part of the PAGES-PMIP working group on Quaternary Interglacials, we propose a protocol to perform transient simulations of the penultimate deglaciation to complement the PMIP4 effort. This design includes time-varying changes in orbital forcing, greenhouse gas concentrations, continental ice-sheets as well as freshwater input from the disintegration of continental ice-sheets. This experiment is designed to assess the coupled response of the climate system to all forcings. Additional sensitivity experiments are proposed to evaluate the response to each forcing. Finally, a selection of paleo records representing different parts of the climate system is presented, providing an appropriate benchmark for upcoming model-data comparisons across the penultimate deglaciation.

scholarly journals Climate evolution across the Mid-Brunhes Transition

2018 ◽  
Vol 14 (12) ◽  
pp. 2071-2087 ◽  
Author(s):  
Aaron M. Barth ◽  
Peter U. Clark ◽  
Nicholas S. Bill ◽  
Feng He ◽  
Nicklas G. Pisias
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
High Amplitude ◽  
Climate System ◽  
Atmospheric Co2 ◽  
Sea Levels ◽  
The Past ◽  
Climate Evolution ◽  
Monsoon Strength ◽  
Climate Variance

Abstract. The Mid-Brunhes Transition (MBT) began ∼ 430 ka with an increase in the amplitude of the 100 kyr climate cycles of the past 800 000 years. The MBT has been identified in ice-core records, which indicate interglaciations became warmer with higher atmospheric CO2 levels after the MBT, and benthic oxygen isotope (δ18O) records, which suggest that post-MBT interglaciations had higher sea levels and warmer temperatures than pre-MBT interglaciations. It remains unclear, however, whether the MBT was a globally synchronous phenomenon that included other components of the climate system. Here, we further characterize changes in the climate system across the MBT through statistical analyses of ice-core and δ18O records as well as sea-surface temperature, benthic carbon isotope, and dust accumulation records. Our results demonstrate that the MBT was a global event with a significant increase in climate variance in most components of the climate system assessed here. However, our results indicate that the onset of high-amplitude variability in temperature, atmospheric CO2, and sea level at ∼430 ka was preceded by changes in the carbon cycle, ice sheets, and monsoon strength during Marine Isotope Stage (MIS) 14 and MIS 13.

scholarly journals Climate evolution across the Mid-Brunhes Transition

2018 ◽  
Author(s):  
Aaron M. Barth ◽  
Peter U. Clark ◽  
Nicholas S. Bill ◽  
Feng He ◽  
Nicklas G. Pisias
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
High Amplitude ◽  
Climate System ◽  
Atmospheric Co2 ◽  
Sea Levels ◽  
The Past ◽  
Climate Evolution ◽  
Monsoon Strength ◽  
Climate Variance

Abstract. The Mid-Brunhes Transition (MBT) began ∼ 430 ka with an increase in the amplitude of the 100-kyr climate cycles of the past 800,000 years. The MBT has been identified in ice-core records, which indicate interglaciations became warmer with higher atmospheric CO2 levels after the MBT, and benthic oxygen isotope (δ18O) records, which suggest that post-MBT interglaciations had higher sea levels than pre-MBT interglaciations. It remains unclear, however, whether the MBT was a globally synchronous phenomenon that included other components of the climate system. Here we further characterize changes in the climate system across the MBT through statistical analyses of ice-core and δ18O records as well as sea-surface temperature, benthic carbon isotope, and dust accumulation records. Our results demonstrate that the MBT was a global event with a significant increase in climate variance in most components of the climate system assessed here. However, our results indicate that the onset of high-amplitude variability in temperature, atmospheric CO2, and sea level at ∼ 430 ka was preceded by changes in the carbon cycle, ice sheets, and monsoon strength during MIS 14 and 13.

Milankovitch Theory of Ice Ages: Hypothesis of Ice-Sheet Linkage Between Regional Insolation and Global Climate

1983 ◽  
Vol 20 (2) ◽  
pp. 125-144 ◽  
Author(s):  
George H. Denton ◽  
Terence J. Hughes
Keyword(s):  
Sea Level ◽  
Northern Hemisphere ◽  
Late Quaternary ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Sea Level Change ◽  
Heat Sinks ◽  
Ice Streams ◽  
Level Change ◽  
Astronomical Theory

J. D. Hays, J. Imbrie, and N. J. Shackleton (1976, Science 194, 1121–1132) showed that the astronomical theory explained many features of late Quaternary ice-age climates, but they did not specify the physical mechanisms involved. Here it is proposed that interlocked variations of ice-sheet heat sinks in both polar hemispheres amplified and transmitted Milankovitch summer half-year insolation changes (a version of the astronomical theory) between 45° and 75°N into the globally synchronous climate changes recorded in geologic records. It is suggested that late Quaternary ice sheets had terrestrial components (grounded above sea level, melting margins, fluctuations controlled by climate) and marine components (grounded below sea level, drained largely by ice streams, limited melting margins, fluctuations controlled primarily by sea level and secondarily by climate, interior surface elevations coupled to downdraw through ice streams). Northern Hemisphere ice sheets were largely marine (with minor melting margins) in the Arctic and terrestrial (with major melting margins) in the midlatitudes. West Antarctic and peripheral East Antarctic ice was marine-based and lacked melting margins. Because of their geographic array, these terrestrial and marine components formed an ice-sheet system whose variations were coupled on a global scale. Milankovitch summer isolation changes near midlatitude Northern Hemisphere melting margins controlled most variations of this system, because advance or retreat of melting margins initiated concurrent eustatic sea-level change. Such sea-level change afforded the critical interlocking mechanism between terrestrial and marine components because it forced simultaneous expansion or contraction of marine margins in both polar hemispheres. This initiated an amplifying feedback loop among all marine components and influenced interior downdraw through ice streams. Arctic summer insolation change was less important because northern melting margins were relatively minor. Its greatest influence was on surface ablation of ice streams that controlled interior downdraw. This affected eustatic sea level and activated global linkage of marine sectors. By analogy with present-day Antarctica, late Quaternary ice sheets were enormous planetary heat sinks due to their reflective and radiative surface characteristics. It is suggested that the effectiveness of these ice-sheet heat sinks varied with their areal extent and interior surface elevation. Thus, it is postulated that concurrent growth or decay of these interlocked ice-sheet heat sinks in both polar hemispheres served as the global amplifier of regional Milankovitch summer insolation.

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