scholarly journals Widening of the Hadley Cell from Last Glacial Maximum to Future Climate

2017 ◽  
Vol 31 (1) ◽  
pp. 267-281 ◽  
Author(s):  
Seok-Woo Son ◽  
Seo-Yeon Kim ◽  
Seung-Ki Min
Keyword(s):  
Last Glacial Maximum ◽  
Climate Model ◽  
Coupled Model ◽  
Glacial Maximum ◽  
Future Climate ◽  
Hadley Cell ◽  
Zero Crossing ◽  
Model Simulations ◽  
Last Glacial ◽  
Intercomparison Project

Abstract The Hadley cell (HC) change from paleoclimate to future climate is examined by comparing coupled model simulations archived for the Paleoclimate Modeling Intercomparison Project phase 3 (PMIP3) and phase 5 of the Coupled Model Intercomparison Project (CMIP5). Specifically, HC width and strength are evaluated using 100-yr equilibrium simulations for the Last Glacial Maximum (LGM), preindustrial (PI), and extended concentration pathway 4.5 (ECP4.5) conditions. Where available, ECP8.5 simulations are also examined to increase the sample size. All models show a systematic widening of the HC from the LGM to the PI and to the ECP4.5 and ECP8.5 simulations. Such widening, which is found in both hemispheres with more robust change in the Southern Hemisphere (SH) than in the Northern Hemisphere (NH), is significantly correlated with global-mean surface air temperature change and the associated static stability change in the subtropics. Based on the zero-crossing latitude of 500-hPa mass streamfunction, about 4.5° latitude widening of the HC results from global warming of 10°C. HC strength also exhibits a systematic weakening in the NH. However, in the SH, HC strength shows a rather minor change from LGM to ECP4.5 conditions because of the cancellation between HC weakening during the austral summer–fall and its strengthening during the spring. This result, which suggests no systematic relationship between HC width and strength changes, is discussed in the context of quasigeostrophic zonal-mean dynamics. Overall findings are also compared with recent studies that are based on transient climate model simulations.

scholarly journals The PMIP4 contribution to CMIP6 – Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments

2017 ◽  
Author(s):  
Masa Kageyama ◽  
Samuel Albani ◽  
Pascale Braconnot ◽  
Sandy P. Harrison ◽  
Peter O. Hopcroft ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Land Surface ◽  
Climate Model ◽  
Model Performance ◽  
Coupled Model ◽  
Glacial Maximum ◽  
Current Phase ◽  
Last Glacial ◽  
Sensitivity Experiments ◽  
Intercomparison Project

Abstract. The Last Glacial Maximum (LGM, 21,000 years ago) is one of the suite of paleoclimate simulations included in the current phase of the Coupled Model Intercomparison Project (CMIP6). It is an interval when insolation was similar to present, but global ice volume was at a maximum, eustatic sea level was at or close to a minimum, greenhouse gas concentrations were lower, atmospheric aerosol loadings were higher than today, and vegetation and land-surface characteristics were different from today. The LGM has been a focus for the Paleoclimate Modelling Intercomparison Project (PMIP) since its inception, and thus many of the problems that might be associated with simulating such a radically different climate are well documented. The LGM state provides an ideal case study for evaluating climate model performance because the changes in forcing and temperature between the LGM and pre-industrial are of the same order of magnitude as those projected for the end of the 21st century. Thus, the CMIP6 LGM experiment could provide additional information that can be used to constrain estimates of climate sensitivity. The design of the Tier 1 LGM experiment (lgm) includes an assessment of uncertainties in boundary conditions, in particular through the use of different reconstructions of the ice sheets and of the change in dust forcing. Additional sensitivity experiments have been designed to quantify feedbacks associated with land-surface changes and aerosol loadings, and to isolate the role of individual forcings. Model analysis and evaluation will capitalise on the relative abundance of palaeoenvironmental observations and quantitative climate reconstructions already available for the LGM.

scholarly journals The PMIP4 contribution to CMIP6 – Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments

2017 ◽  
Vol 10 (11) ◽  
pp. 4035-4055 ◽  
Author(s):  
Masa Kageyama ◽  
Samuel Albani ◽  
Pascale Braconnot ◽  
Sandy P. Harrison ◽  
Peter O. Hopcroft ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Land Surface ◽  
Climate Model ◽  
Model Performance ◽  
Coupled Model ◽  
Glacial Maximum ◽  
Current Phase ◽  
Last Glacial ◽  
Sensitivity Experiments ◽  
Intercomparison Project

Abstract. The Last Glacial Maximum (LGM, 21 000 years ago) is one of the suite of paleoclimate simulations included in the current phase of the Coupled Model Intercomparison Project (CMIP6). It is an interval when insolation was similar to the present, but global ice volume was at a maximum, eustatic sea level was at or close to a minimum, greenhouse gas concentrations were lower, atmospheric aerosol loadings were higher than today, and vegetation and land-surface characteristics were different from today. The LGM has been a focus for the Paleoclimate Modelling Intercomparison Project (PMIP) since its inception, and thus many of the problems that might be associated with simulating such a radically different climate are well documented. The LGM state provides an ideal case study for evaluating climate model performance because the changes in forcing and temperature between the LGM and pre-industrial are of the same order of magnitude as those projected for the end of the 21st century. Thus, the CMIP6 LGM experiment could provide additional information that can be used to constrain estimates of climate sensitivity. The design of the Tier 1 LGM experiment (lgm) includes an assessment of uncertainties in boundary conditions, in particular through the use of different reconstructions of the ice sheets and of the change in dust forcing. Additional (Tier 2) sensitivity experiments have been designed to quantify feedbacks associated with land-surface changes and aerosol loadings, and to isolate the role of individual forcings. Model analysis and evaluation will capitalize on the relative abundance of paleoenvironmental observations and quantitative climate reconstructions already available for the LGM.

scholarly journals Clumped isotope constraints on changes in latest Pleistocene hydroclimate in the northwestern Great Basin: Lake Surprise, California

2020 ◽  
Vol 132 (11-12) ◽  
pp. 2669-2683
Author(s):  
L.M. Santi ◽  
A.J. Arnold ◽  
D.E. Ibarra ◽  
C.A. Whicker ◽  
J.A. Mering ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Great Basin ◽  
Climate Model ◽  
Glacial Maximum ◽  
Model Simulations ◽  
Last Glacial ◽  
Climate Forcings ◽  
Clumped Isotope ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract During the Last Glacial Maximum (LGM) and subsequent deglaciation, the Great Basin in the southwestern United States was covered by numerous extensive closed-basin lakes, in stark contrast with the predominately arid climate observed today. This transition from lakes in the Late Pleistocene to modern aridity implies large changes in the regional water balance. Whether these changes were driven by increased precipitation rates due to changes in atmospheric dynamics, decreased evaporation rates resulting from temperature depression and summer insolation changes, or some combination of the two remains uncertain. The factors contributing to these large-scale changes in hydroclimate are critical to resolve, given that this region is poised to undergo future anthropogenic-forced climate changes with large uncertainties in model simulations for the 21st century. Furthermore, there are ambiguous constraints on the magnitude and even the sign of changes in key hydroclimate variables between the Last Glacial Maximum and the present day in both proxy reconstructions and climate model analyses of the region. Here we report thermodynamically derived estimates of changes in temperature, precipitation, and evaporation rates, as well as the isotopic composition of lake water, using clumped isotope data from an ancient lake in the northwestern Great Basin, Lake Surprise (California). Compared to modern climate, mean annual air temperature at Lake Surprise was 4.7 °C lower during the Last Glacial Maximum, with decreased evaporation rates and similar precipitation rates to modern. During the mid-deglacial period, the growth of Lake Surprise implied that the lake hydrologic budget briefly departed from steady state. Our reconstructions indicate that this growth took place rapidly, while the subsequent lake regression took place over several thousand years. Using models for precipitation and evaporation constrained from clumped isotope results, we determine that the disappearance of Lake Surprise coincided with a moderate increase in lake temperature, along with increasing evaporation rates outpacing increasing precipitation rates. Concomitant analysis of proxy data and climate model simulations for the Last Glacial Maximum are used to provide a robust means to understand past climate change, and by extension, predict how current hydroclimates may respond to expected future climate forcings. We suggest that an expansion of this analysis to more basins across a larger spatial scale could provide valuable insight into proposed climate forcings, and aid in climate model process depiction. Ultimately, our analysis highlights the importance of temperature-driven evaporation as a mechanism for lake growth and retreat in this region.

scholarly journals Last Glacial Maximum conditions in southern Africa

2014 ◽  
Vol 38 (5) ◽  
pp. 519-542 ◽  
Author(s):  
Abi E.C. Stone
Keyword(s):  
Numerical Model ◽  
Last Glacial Maximum ◽  
Southern Africa ◽  
Conceptual Models ◽  
Climate Model ◽  
Climatic Conditions ◽  
Glacial Maximum ◽  
Data Sets ◽  
Model Simulations ◽  
Last Glacial

The Last Glacial Maximum (LGM) (21±2 ka) is an important period for which to understand past climatic and environmental conditions. In particular it is a key time-slice for evaluating the performance of numerical climate model simulations of glacial palaeoclimates using palaeoenvironmental data sets. However, our palaeoenvironmental data sets and reconstructions of climatic conditions at the LGM are still debated in certain regions. This is the case for southern Africa, despite more than half a century of research since early conceptual models of palaeoclimate were proposed. The greatest debates are about the spatial patterning of relatively wetter and drier conditions than present and the position of the mid-latitude westerlies at the LGM. Different patterns emerge from: separate syntheses of palaeoenvironmental proxies, from different numerical model simulations and from comparisons of the two. In this review of the progress over half a century of research in southern Africa: (1) a brief historical review of key conceptual models is given, (2) key points of conflict that emerge in synthesis of palaeoenvironmental proxy records are outlined and (3) numerical model simulations are considered. From these, some points for future progress are suggested.

scholarly journals Global peatlands under future climate – seamless model projections from the Last Glacial Maximum

2021 ◽  
Author(s):  
Jurek Müller ◽  
Fortunat Joos
Keyword(s):  
Last Glacial Maximum ◽  
Climate Model ◽  
Coupled Model ◽  
Glacial Maximum ◽  
Dynamic Global Vegetation Model ◽  
Last Glacial ◽  
The Future ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Peatlands are diverse wetland ecosystems distributed mostly over the northern latitudes and tropics. Globally they store a large portion of the global soil organic carbon and provide important ecosystem services. The future of these systems under continued anthropogenic warming and direct human disturbance has potentially large impacts on atmospheric CO2 and climate. We performed global long term projections of peatland area and carbon over the next 5000 years using a dynamic global vegetation model forced with climate anomalies from ten models of the Coupled Model Intercomparison Project (CMIP6) and three scenarios. These projections are continued from a transient simulation from the Last Glacial Maximum to the present to account for the full transient history. Our results suggest short to long term net losses of global peatland area and carbon, with higher losses under higher emission scenarios. Large parts of today's active northern peatlands are at risk. Conditions for peatlands in the tropics and, in case of mitigation, eastern Asia and western north America improve. Factorial simulations reveal committed historical changes and future rising temperature as the main driver of future peatland loss and increasing precipitations as driver for regional peatland expansion. Additional simulations forced with two CMIP6 scenarios extended transiently beyond 2100, show qualitatively similar results to the standard scenarios, but highlight the importance of extended future scenarios for long term carbon cycle projections. The spread between simulations forced with different climate model anomalies suggests a large uncertainty in projected peatland variables due to uncertain climate forcing. Our study highlights the importance of quantifying the future peatland feedback to the climate system and its inclusion into future earth system model projections.

scholarly journals Breakdown of the Linear Relationship between the Southern Hemisphere Hadley Cell Edge and Jet Latitude Changes in the Last Glacial Maximum

2020 ◽  
Vol 33 (13) ◽  
pp. 5713-5725
Author(s):  
Seo-Yeon Kim ◽  
Seok-Woo Son
Keyword(s):  
Southern Hemisphere ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Cold Climate ◽  
Hadley Cell ◽  
Last Glacial ◽  
Intercomparison Project ◽  
Mean Circulation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractA poleward displacement of the Hadley cell (HC) edge and the eddy-driven jet latitude has been observed in the Southern Hemisphere (SH) during the last few decades. This change is further projected to continue in the future, indicating coherent tropical and extratropical zonal-mean circulation changes from the present climate to a warm climate. Here we show that such a systematic change in the zonal-mean circulation change does not hold in a cold climate. By examining the Last Glacial Maximum (LGM), preindustrial (PI), and extended concentration pathway 4.5 (ECP4.5) scenarios archived for phase 3 of the Paleoclimate Modeling Intercomparison Project (PMIP3) and phase 5 of the Coupled Model Intercomparison Project (CMIP5), it is shown that while the annual-mean SH HC edge systematically shifts poleward from the LGM scenario to the PI scenario and then to the ECP4.5 scenario the annual-mean SH eddy-driven jet latitude does not. All models show a poleward jet shift from the PI scenario to the ECP4.5 scenario, but over one-half of the models exhibit no trend or even an equatorward jet shift from the LGM scenario to the PI scenario. This decoupling between the HC edge and jet latitude changes is most pronounced in SH winter when the Antarctic surface cooling in the LGM scenario is comparable to or larger than the tropical upper-tropospheric cooling. This result indicates that polar amplification could play a crucial role in driving the decoupling of the tropical and midlatitude zonal-mean circulation in the SH in a cold climate.

Ice Age Winds: An Aquaplanet Model

2006 ◽  
Vol 19 (9) ◽  
pp. 1706-1715 ◽  
Author(s):  
Gareth P. Williams ◽  
Kirk Bryan
Keyword(s):  
Last Glacial Maximum ◽  
Coupled Model ◽  
Glacial Maximum ◽  
Hadley Cell ◽  
Ice Age ◽  
Moist Convection ◽  
Surface Cooling ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract Factors controlling the position and strength of the surface winds during the Last Glacial Maximum (LGM) are examined using a global, multilevel, moist, atmospheric model. The idealized aquaplanet model is bounded below by a prescribed axisymmetric temperature distribution that corresponds to an ocean-covered surface. Various forms of this distribution are used to examine the influence of changes in the surface cooling and baroclinicity rates. The model omits seasonal variations. Increasing the cooling lowers the tropopause and greatly reduces the moist convection in the Tropics, thereby causing a weakening and equatorward contraction of the Hadley cell. Such a cooling also weakens the surface westerlies and shifts the peak westerly stress equatorward. An extra surface baroclinicity in midlatitudes—implicitly associated with an increase in the polar sea ice—also shifts the peak westerly stress equatorward, but strengthens the surface westerlies. Thus, calculations with combined surface cooling and baroclinicity increases, representative of the Last Glacial Maximum, reveal an absence of change in the amplitude of the peak westerly stress but exhibit a substantial equatorward shift in its position, 7° for a 3-K cooling and 11° for a 6-K cooling. The easterlies, however, always increase in strength when the surface westerlies move equatorward. The application of these results to the LGM must take into account the model’s assumption of symmetry between the two hemispheres. Any changes in the climate’s hemispheric asymmetry could also cause comparable latitudinal shifts in the westerlies, probably of opposite sign in the two hemispheres. Published coupled-model simulations for the LGM give an equatorward shift for the peak westerlies in the Northern Hemisphere but give contradictory results for the Southern Hemisphere.

scholarly journals Metric-Dependent Tendency of Tropical Belt Width Changes during the Last Glacial Maximum

2018 ◽  
Vol 31 (20) ◽  
pp. 8527-8540 ◽  
Author(s):  
Na Wang ◽  
Dabang Jiang ◽  
Xianmei Lang
Keyword(s):  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Hadley Cell ◽  
The Other ◽  
Total Width ◽  
Last Glacial ◽  
Intercomparison Project ◽  
Belt Width ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Motivated by studies of tropical expansion under modern global warming, the behavior of the tropical belt during the Last Glacial Maximum (LGM) relative to the preindustrial period has been investigated in this study, using simulations from phase 3 of the Paleoclimate Modelling Intercomparison Project (PMIP3) under the framework of phase 5 of the Coupled Model Intercomparison Project (CMIP5). The tropical belt width changes determined by multiple metrics present two opposite tendencies. One refers to the poleward migration of the tropical edge as measured by the steep tropopause gradient and the subtropical jet, and the other suggests that the LGM tropics become narrower as measured by the Hadley cell extent, the eddy-driven jet, and the latitude where precipitation minus evaporation equals zero. The magnitude of such changes widely differs across models and metrics. In absolute terms, the multimodel mean total width changes range from 0.6° to 1.7° among metrics, with contributions predominantly from the Northern Hemisphere. Furthermore, the two metrics that indicate tropical widening are located in the upper troposphere. Such widening is closely related to the vertical and meridional temperature gradient changes in the subtropical regions. The other metrics are located in the middle and lower troposphere, and their variations are directly or indirectly related to changes in the low-level baroclinicity. The diverse responses of metrics to the LGM boundary conditions suggest that the tropical belt width changes and their climatic impacts are distinguished by the different measurements. The selection of metrics should correspond to the specific tropical properties of concern.

scholarly journals Different ocean states and transient characteristics in Last Glacial Maximum simulations and implications for deglaciation

2013 ◽  
Vol 9 (5) ◽  
pp. 2319-2333 ◽  
Author(s):  
X. Zhang ◽  
G. Lohmann ◽  
G. Knorr ◽  
X. Xu
Keyword(s):  
Last Glacial Maximum ◽  
Model Comparison ◽  
Climate Model ◽  
Deep Ocean ◽  
Glacial Maximum ◽  
Meridional Overturning Circulation ◽  
Last Deglaciation ◽  
New Paradigm ◽  
Last Glacial ◽  
The Last Deglaciation

Abstract. The last deglaciation is one of the best constrained global-scale climate changes documented by climate archives. Nevertheless, understanding of the underlying dynamics is still limited, especially with respect to abrupt climate shifts and associated changes in the Atlantic meridional overturning circulation (AMOC) during glacial and deglacial periods. A fundamental issue is how to obtain an appropriate climate state at the Last Glacial Maximum (LGM, 21 000 yr before present, 21 ka BP) that can be used as an initial condition for deglaciation. With the aid of a comprehensive climate model, we found that initial ocean states play an important role on the equilibrium timescale of the simulated glacial ocean. Independent of the initialization, the climatological surface characteristics are similar and quasi-stationary, even when trends in the deep ocean are still significant, which provides an explanation for the large spread of simulated LGM ocean states among the Paleoclimate Modeling Intercomparison Project phase 2 (PMIP2) models. Accordingly, we emphasize that caution must be taken when alleged quasi-stationary states, inferred on the basis of surface properties, are used as a reference for both model inter-comparison and data model comparison. The simulated ocean state with the most realistic AMOC is characterized by a pronounced vertical stratification, in line with reconstructions. Hosing experiments further suggest that the response of the glacial ocean is dependent on the ocean background state, i.e. only the state with robust stratification shows an overshoot behavior in the North Atlantic. We propose that the salinity stratification represents a key control on the AMOC pattern and its transient response to perturbations. Furthermore, additional experiments suggest that the stratified deep ocean formed prior to the LGM during a time of minimum obliquity (~ 27 ka BP). This indicates that changes in the glacial deep ocean already occur before the last deglaciation. In combination, these findings represent a new paradigm for the LGM and the last deglaciation, which challenges the conventional evaluation of glacial and deglacial AMOC changes based on an ocean state derived from 21 ka BP boundary conditions.

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