scholarly journals Individual and combined effects of ice sheets and precession on MIS-13 climate

2009 ◽  
Vol 5 (1) ◽  
pp. 557-593
Author(s):  
Q. Z. Yin ◽  
A. Berger ◽  
M. Crucifix
Keyword(s):  
Northern Hemisphere ◽  
Asian Summer Monsoon ◽  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Summer Precipitation ◽  
East China ◽  
Asian Summer ◽  
The Last Glacial

Abstract. Simulations with an Earth System Model of Intermediate Complexity are made to investigate the role of insolation and the size of ice sheets on the regional and global climate for marine isotope stage (MIS) 13. The astronomical forcing is selected at two dates with opposite precession, one when Northern Hemisphere summer (NHS) occurs at perihelion (at 506 ka BP) and the other when it occurs at aphelion (at 495 ka BP). Experiments with five different volumes of the Eurasian and North American ice sheets (ranging from 0 to the Last Glacial Maximum one) are done under these two astronomical conditions. When NHS is at perihelion, the Earth is warmer, the seasonal contrast in Northern (Southern) Hemisphere is larger (smaller) and summer precipitation in Northern Hemisphere monsoon regions is more abundant than when it is at aphelion. The global cooling due to the ice sheets is mainly related to the ice sheet area, little to their height. The regional cooling and warming anomalies caused by the ice sheets get intensified with increasing ice sheet size. The cooling is different whether the NHS occurs at aphelion or at perihelion. Precipitation over different monsoon regions responds differently to the size of the ice sheets. Over North Africa, the ice sheets always reduce precipitation, larger the size less the precipitation. Over East China, when NHS is at perihelion, the ice sheets reinforce the summer precipitation whatever their sizes. But when NHS is at aphelion, there is a threshold in the ice volume beyond which the ice sheets start to reduce the precipitation over East China. This underlies the importance of insolation in shaping the ice sheet impact on the precipitation over the East Asian Summer Monsoon (EASM) region.

scholarly journals Individual and combined effects of ice sheets and precession on MIS-13 climate

2009 ◽  
Vol 5 (2) ◽  
pp. 229-243 ◽  
Author(s):  
Q. Z. Yin ◽  
A. Berger ◽  
M. Crucifix
Keyword(s):  
Global Climate ◽  
Wave Train ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Summer Precipitation ◽  
East China ◽  
Thermal Contrast ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. An Earth System Model of Intermediate Complexity is used to investigate the role of insolation and of the size of ice sheets on the regional and global climate of marine isotope stage (MIS) 13. The astronomical forcing is selected at two dates with opposite precession, one when northern hemisphere (NH) summer occurs at perihelion (at 506 ka (1 ka=1000 years) BP), and the other when it occurs at aphelion (at 495 ka BP). Five different volumes of the Eurasian ice sheet (EA) and North American ice sheet (NA), ranging from 0 to the Last Glacial Maximum (LGM) one, are used. The global cooling due to the ice sheets is mainly related to their area, little to their height. The regional cooling and warming anomalies caused by the ice sheets intensify with increasing size. Precipitation over different monsoon regions responds differently to the size of the ice sheets. Over North Africa and India, precipitation decreases with increasing ice sheet size due to the southward shift of the Intertropical Convergence Zone (ITCZ), whatever the astronomical configuration is. However, the situation is more complicated over East Asia. The ice sheets play a role through both reducing the land/ocean thermal contrast and generating a wave train which is topographically induced by the EA ice sheet. This wave train contributes to amplify the Asian land/ocean pressure gradient in summer and finally reinforces the precipitation. The presence of this wave train depends on the combined effect of the ice sheet size and insolation. When NH summer occurs at perihelion, the EA is able to induce this wave train whatever its size is, and this wave train plays a more important role than the reduction of the land/ocean thermal contrast. Therefore, the ice sheets reinforce the summer precipitation over East China whatever their sizes are. However, when NH summer occurs at aphelion, there is a threshold in the ice volume beyond which the wave train is not induced anymore. Therefore, below this threshold, the wave train effect is dominant and the ice sheets reinforce precipitation over East China. Beyond this threshold, the ice sheets reduce the precipitation mainly through reducing the land/ocean thermal contrast.

scholarly journals Investigating the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle

2009 ◽  
Vol 5 (3) ◽  
pp. 329-345 ◽  
Author(s):  
S. Bonelli ◽  
S. Charbit ◽  
M. Kageyama ◽  
M.-N. Woillez ◽  
G. Ramstein ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Glacial Cycle ◽  
Last Glacial ◽  
Atmospheric Co2 Concentration ◽  
The Last Glacial

Abstract. A 2.5-dimensional climate model of intermediate complexity, CLIMBER-2, fully coupled with the GREMLINS 3-D thermo-mechanical ice sheet model is used to simulate the evolution of major Northern Hemisphere ice sheets during the last glacial-interglacial cycle and to investigate the ice sheets responses to both insolation and atmospheric CO2 concentration. This model reproduces the main phases of advance and retreat of Northern Hemisphere ice sheets during the last glacial cycle, although the amplitude of these variations is less pronounced than those based on sea level reconstructions. At the last glacial maximum, the simulated ice volume is 52.5×1015 m3 and the spatial distribution of both the American and Eurasian ice complexes is in reasonable agreement with observations, with the exception of the marine parts of these former ice sheets. A set of sensitivity studies has also been performed to assess the sensitivity of the Northern Hemisphere ice sheets to both insolation and atmospheric CO2. Our results suggest that the decrease of summer insolation is the main factor responsible for the early build up of the North American ice sheet around 120 kyr BP, in agreement with benthic foraminifera δ18O signals. In contrast, low insolation and low atmospheric CO2 concentration are both necessary to trigger a long-lasting glaciation over Eurasia.

scholarly journals Influence of ablation-related processes in the built-up of simulated Northern Hemisphere ice sheets during the last glacial cycle

2012 ◽  
Vol 6 (6) ◽  
pp. 4897-4938 ◽  
Author(s):  
S. Charbit ◽  
C. Dumas ◽  
M. Kageyama ◽  
D. M. Roche ◽  
C. Ritz
Keyword(s):  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Cycle ◽  
Satisfactory Description ◽  
Last Glacial ◽  
Transient Simulations ◽  
Main Driver ◽  
The Impact ◽  
The Last Glacial

Abstract. Since the original formulation of the positive-degree-day (PDD) method, different PDD calibrations have been proposed in the literature in response to the increasing number of observations. Although these formulations provide a satisfactory description of the present-day Greenland geometry, they have not all been tested for paleo ice sheets. Using the climate-ice sheet model CLIMBER-GRISLI coupled with different PDD models, we evaluate how the parameterization of the ablation may affect the evolution of Northern Hemisphere ice sheets in the transient simulations of the last glacial cycle. Results from fully coupled simulations are compared to time-slice experiments carried out at different key periods of the last glacial period. We find large differences in the simulated ice sheets according to the chosen PDD model. These differences occur as soon as the onset of glaciation, therefore affecting the subsequent evolution of the ice system. To further investigate how the PDD method controls this evolution, special attention is given to the role of each PDD parameter. We show that glacial inception is critically dependent on the representation of the impact of the temperature variability from the daily to the inter-annual time scale, whose effect is modulated by the refreezing scheme. Finally, an additional set of sensitivity experiments has been carried out to assess the relative importance of melt processes with respect to initial ice sheet configuration in the construction and the evolution of past Northern Hemisphere ice sheets. Our analysis reveals that the impacts of the initial ice sheet condition may range from quite negligible to explaining about half of the LGM ice volume depending on the representation of stochastic temperature variations which remain the main driver of the evolution of the ice system.

scholarly journals The sensitivity of Northern Hemisphere ice sheets to atmospheric forcing during the last glacial cycle using PMIP3 models

2019 ◽  
Vol 65 (252) ◽  
pp. 645-661 ◽  
Author(s):  
LU NIU ◽  
GERRIT LOHMANN ◽  
SEBASTIAN HINCK ◽  
EVAN J. GOWAN ◽  
UTA KREBS-KANZOW
Keyword(s):  
Northern Hemisphere ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Climate Forcing ◽  
Phase Iii ◽  
Temperature Pattern ◽  
Glacial Cycle ◽  
Large Variability ◽  
Last Glacial ◽  
The Last Glacial

ABSTRACTThe evolution of Northern Hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one General Circulation Model, COSMOS. By comparing the simulated results to geological reconstructions, we first show that the modelled climate is capable of capturing the main features of the ice-sheet evolution. However, large deviations exist, likely due to the absence of nonlinear interactions between ice sheet and other climate components. The model uncertainties of the climate forcing are examined using the output from nine climate models from the Paleoclimate Modelling Intercomparison Project Phase III. The results show a large variability in simulated ice sheets between the different models. We find that the ice-sheet extent pattern resembles summer surface air temperature pattern at the Last Glacial Maximum, confirming the dominant role of surface ablation process for high-latitude Northern Hemisphere ice sheets. This study shows the importance of the upper boundary condition for ice-sheet modelling, and implies that careful constraints on climate output is essential for simulating realistic glacial Northern Hemisphere ice sheets.

scholarly journals Numerical reconstructions of the Northern Hemisphere ice sheets through the last glacial-interglacial cycle

2007 ◽  
Vol 3 (1) ◽  
pp. 15-37 ◽  
Author(s):  
S. Charbit ◽  
C. Ritz ◽  
G. Philippon ◽  
V. Peyaud ◽  
M. Kageyama
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Maximum Amplitude ◽  
The Other ◽  
Climate Forcing ◽  
Last Glacial ◽  
Ice Volume ◽  
The Last Glacial

Abstract. A 3-dimensional thermo-mechanical ice-sheet model is used to simulate the evolution of the Northern Hemisphere ice sheets through the last glacial-interglacial cycle. The ice-sheet model is forced by the results from six different atmospheric general circulation models (AGCMs). The climate evolution over the period under study is reconstructed using two climate equilibrium simulations performed for the Last Glacial Maximum (LGM) and for the present-day periods and an interpolation through time between these snapshots using a glacial index calibrated against the GRIP δ18O record. Since it is driven by the timing of the GRIP signal, the temporal evolution of the ice volume and the ice-covered area is approximately the same from one simulation to the other. However, both ice volume curves and spatial distributions of the ice sheets present some major differences from one AGCM forcing to the other. The origin of these differences, which are most visible in the maximum amplitude of the ice volume, is analyzed in terms of differences in climate forcing. This analysis allows for a partial evaluation of the ability of GCMs to simulate climates consistent with the reconstructions of past ice sheets. Although some models properly reproduce the advance or retreat of ice sheets in some specific areas, none of them is able to reproduce both North American or Eurasian ice complexes in full agreement with observed sea-level variations and geological data. These deviations can be attributed to shortcomings in the climate forcing and in the LGM ice-sheet reconstruction used as a boundary condition for GCM runs, but also to missing processes in the ice-sheet model itself.

scholarly journals A three-dimensional climate—ice-sheet model applied to the Last Glacial Maximum

1997 ◽  
Vol 25 ◽  
pp. 333-339 ◽  
Author(s):  
Philippe Huybrechts ◽  
Stephen T’siobbel
Keyword(s):  
Last Glacial Maximum ◽  
Northern Hemisphere ◽  
Climate Model ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

A quasi-three-dimensional (3-D) climate model (Sellers, 1983) was used to simulate the climate of the Last Glacial Maximum (LGM) in order to provide climatic input for the modelling of the Northern Hemisphere ice sheets. The climate model is basically a coarse-gridded general circulation (GCM) with simplified dynamics, and was subject to appropriate boundary conditions for ice-sheet elevation, atmospheric CO2concentration and orbital parameters. When compared with the present-daysimulation, the simulated climate at the Last Glacial Maximum is characterized by a global annual cooling of 3.5°C and a reduction in global annualprecipitation of 7.5%, which agrees well with results from other, more complex GCMs. Also the patterns of temperature change compare fairly with mostother GCM results, except for a smaller cooling over the North Atlantic and the larger cooling predicted for the summer rather than for the winter over Eurasia.The climate model is able to simulate changes in Northern Hemisphere tropospheric circulation, yielding enhanced westerlies in the vicinity of the Laurentide and Eurasian ice sheets. However, the simulated precipitation patterns are less convincing, and show a distinct mean precipitation increase over the Laurentide ice sheet. Nevertheless, when using the mean-monthly fields of LGM minus present-day anomalies of temperature and precipitation rate to drive a three-dimensional thermomechanical ice-sheet model, it was demonstrated that within realistic bounds of the ice-flow and mass-balance parameters, veryreasonable reconstructions of the Last Glacial Maximum ice sheets could be obtained.

scholarly journals Hydrological Response of East China to the Variation of East Asian Summer Monsoon

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Fuxing Li ◽  
Dong Chen ◽  
Qiuhong Tang ◽  
Wenhong Li ◽  
Xuejun Zhang
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Yellow River ◽  
Asian Summer Monsoon ◽  
Global Climate ◽  
East Asian ◽  
Management Strategies ◽  
East China ◽  
Severe Drought ◽  
Asian Summer

The sensitivity of hydrologic variables in East China, that is, runoff, precipitation, evapotranspiration, and soil moisture to the fluctuation of East Asian summer monsoon (EASM), is evaluated by the Mann-Kendall correlation analysis on a spatial resolution of 1/4° in the period of 1952–2012. The results indicate remarkable spatial disparities in the correlation between the hydrologic variables and EASM. The regions in East China susceptible to hydrological change due to EASM fluctuation are identified. When the standardized anomaly of intensity index of EASM (EASMI) is above 1.00, the runoff of Haihe basin has increased by 49% on average, especially in the suburb of Beijing and Hebei province where the runoff has increased up to 105%. In contrast, the runoff in the basins of Haihe and Yellow River has decreased by about 27% and 17%, respectively, when the standardized anomaly of EASMI is below −1.00, which has brought severe drought to the areas since mid-1970s. The study can be beneficial for national or watershed agencies developing adaptive water management strategies in the face of global climate change.

Dynamic Effect of Last Glacial Maximum Ice Sheet Topography on the East Asian Summer Monsoon

2020 ◽  
Vol 33 (16) ◽  
pp. 6929-6944 ◽  
Author(s):  
Yu Gao ◽  
Zhengyu Liu ◽  
Zhengyao Lu
Keyword(s):  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Stationary Wave ◽  
Westerly Jet ◽  
Asian Summer ◽  
Ice Sheet Topography

AbstractThe effect of ice sheet topography on the East Asian summer monsoon (EASM) during the Last Glacial Maximum is studied using CCSM3 in a hierarchy of model configurations. It is found that receding ice sheets result in a weakened EASM, with the reduced ice sheet thickness playing a major role. The lower ice sheet topography weakens the EASM through shifting the position of the midlatitude jet, and through altering Northern Hemisphere stationary waves. In the jet shifting mechanism, the lowering of ice sheets shifts the westerly jet northward and decreases the westerly jet over the subtropics in summer, which reduces the advection of dry enthalpy and in turn precipitation over the EASM region. In the stationary wave mechanism, the lowering of ice sheets induces an anomalous stationary wave train along the westerly waveguide that propagates into the EASM region, generating an equivalent-barotropic low response; this leads to reduced lower-tropospheric southerlies, which in turn reduces the dry enthalpy advection into East Asia, and hence the EASM precipitation.

Impacts of the PMIP4 ice-sheets on Northern Hemisphere climate during the last glacial period

2020 ◽  
Author(s):  
Kenji Izumi ◽  
Paul Paul Valdes ◽  
Ruza Ivanovic ◽  
Lauren Gregoire
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Model Comparison ◽  
Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Stationary Waves ◽  
Last Glacial ◽  
Intercomparison Project ◽  
The Last Glacial

<p>The Last Glacial Maximum (LGM; 21,000 yr before present) is a target period of the paleoclimate simulations in the Coupled Model Intercomparison Project Phase 6 – the Paleoclimate Modeling Intercomparison Project Phase 4 (CMIP6-PMIP4) because of abundant paleoenvironmental data in continental, ice, and marine indicators. The LGM was a period of low atmospheric trace gases when large ice sheets covered over North America and Scandinavia. Paleoclimate reconstructions and modeling studies suggest that the Northern Hemisphere climate differed from today.</p><p>In this study, we used the coupled atmosphere and ocean model HadCM3B-M1 in order to investigate the impacts of the main LGM boundary condition changes, in particular, the ICE-6G_C, GLAC-1D, and PMIP3 ice-sheet reconstructions following the PMIP4 protocol, on the mean state of the climate over the Northern Hemisphere. First, we check the surface albedo forcing and feedback with a simplified partial derivative method and assess the surface temperature changes and their composition using a simple surface energy balance equation. Then, we investigate how patterns of stationary waves, westerly jet precipitation over the Northern Hemisphere change in response to the LGM ice-sheet configuration. Finally, we implement a paleo data-model comparison for validation of the large-scale climate changes over the Northern Hemisphere at the LGM. The wintertime stationary waves have the largest amplitude and different responses among the experiments, while stationary waves in summer are weak and similar responses. The LGM simulation with the ICE-6G_C better captures features of the LGM climate, but compared to the reconstructions, the climate model tends to overestimate cooling in summer and underestimate cooling in winter and simulate wetter conditions over the Northern Hemisphere.  </p>

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