Dansgaard-Oeschger Tipping Events (TEs): Towards determining if IPCC-relevant models represent these TEs.

Last Glacial Period ◽

Mis 3 ◽

Common Framework ◽

Intercomparison Project ◽

Earth System Models ◽

Paleoclimate Modelling ◽

The Last Glacial ◽

Millennial Scale

<p>Dansgaard-Oeschger (DO) events are abrupt, large climate swings that punctuated the last glacial period. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. This has implications for whether these models are also capable of simulating future TEs,&#160; and more in general, for the delivery of accurate climate change projections. Here we present progress on possible pathways to a DO Paleoclimate Modelling Intercomparison Project (PMIP) protocol. This is broad interest to the climate community since (1), there is currently no PMIP common guidance to investigate DO events, (2) it could help carry out simulations in Earth system models under a common framework, and (3) it will help guide a more methodical search for DO events in current models. A protocol could help investigate cold-period TEs through a range of insolation-, freshwater-, green-house-gas-, and Northern Hemisphere ice sheet-related forcings, as well as evaluating the possibility of spontaneous TEs. MIS3 was a period of noticeable millennial-scale climate variability, characterised by the most regular incidence of DO events (Schulz et al., 1999). Although most abrupt DO events happened during MIS3, only few studies investigate TEs in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we therefore suggest that the MIS3 period could be the focus of such a DO-event focussed modelling protocol. Experiments performed under MIS 3 boundary conditions may help (1) explore variability under intermediate glacial conditions, (2) better understand the mechanisms behind millennial-scale TEs, (3) look for spontaneous DO-type oscillations, and (4) help answer the question: &#8220;are models too stable?&#8221;.</p>

Ice-sheet mass balance during the last glacial maximum

Annals of Glaciology ◽

10.3189/s026030550001394x ◽

1997 ◽

Vol 25 ◽

pp. 145-152 ◽

Cited By ~ 2

Author(s):

Gilles Ramstein ◽

Adeline Fabre ◽

Sophie Pinot ◽

Catherine Ritz ◽

Sylvie Joussaume

Keyword(s):

Last Glacial Maximum ◽

General Circulation ◽

Ice Sheets ◽

Ice Sheet ◽

Glacial Maximum ◽

Last Glacial ◽

Intercomparison Project ◽

The Last Glacial Maximum ◽

In the framework of the Paleoclimate Modelling Intercomparison Project (PMIP), simulations of the Last Glacial Maximum (LGM) have- been performed. More than 10 different atmospheric general circulation models (AGCMs) have been used with the same boundary conditions: sea-surface temperatures prescribed by CLIMAP (1981), ice-sheet reconstruction provided by Peltier (1994), change in insolation, and reduced CO2 content. One of the major questions is to investigate whether the simulations of the LGM are in equilibrium with the prescribed ice-sheet reconstruction. To answer this question, we have used two different approaches. First, we analyze the results of a sel of LGM simulations performed with different versions of the Laboratoire de Meteorolo-gie Dynamique (LMD) AGCM and study the hydrologic and snow- budgets over the Laurcntide and Fennoscandian ice sheets. Second, we use the AGCM outputs to force an ice-sheet model in order to investigate its ability to maintain the ice sheets as reconstructed by CLIMAP (1981) or Peltier (1994).

Possible pathways to a Dansgaard-Oeschger (DO) PMIP protocol

10.5194/egusphere-egu21-8730 ◽

2021 ◽

Author(s):

Irene Malmierca-Vallet ◽

Louise C. Sime ◽

Paul J. Valdes

Keyword(s):

General Circulation ◽

Climate Changes ◽

Ice Age ◽

Climate Change Projections ◽

The Past ◽

External Perturbations ◽

Mis 3 ◽

Last Ice Age ◽

Earth System Models

<p>The DO events of the last ice age represent one of the best studied abrupt climate transitions, yet we still lack a comprehensive explanation for them. There is uncertainty whether current IPCC-relevant models can effectively represent the processes that cause DO events. Current Earth system models (ESMs) seem overly stable against external perturbations and incapable of reproducing most abrupt climate changes of the past (Valdes, 2011). If this holds true, this could noticeably influence their capability to predict future abrupt transitions, with significant consequences for the delivery of precise climate change projections. &#160;In this task, the objectives of this study are (1) to cross compare existing simulations that show spontaneous DO-type oscillations using a common set of diagnostics so we can compare the mechanisms and the characteristics of the oscillations, and (2) to formulate possible pathways to a DO PMIP protocol that could help investigate cold-period instabilities through a range of insolation-, freshwater-, GHG-, and NH ice sheet-related forcings, as well as evaluating the possibility of spontaneous internal oscillations.</p><p>Although most abrupt DO events happened during MIS3, only few studies investigate DO events in coupled general circulation models under MIS 3 conditions (e.g., Kawamura et al., 2017; Zhang and Prange, 2020). Here, we thus propose that the MIS3 period could be the focus of such a DO-event modelling protocol. More specific sensitivity experiments performed under MIS 3 boundary conditions are needed in order to (1) better understand the mechanisms behind millennial-scale climate variability, (2) explore AMOC variability under intermediate glacial conditions, and (3) help answer the question: &#8220;are models too stable?&#8221;.</p>

Ice-sheet mass balance during the last glacial maximum

Annals of Glaciology ◽

10.1017/s026030550001394x ◽

1997 ◽

Vol 25 ◽

pp. 145-152 ◽

Cited By ~ 4

Author(s):

Gilles Ramstein ◽

Adeline Fabre ◽

Sophie Pinot ◽

Catherine Ritz ◽

Sylvie Joussaume

Keyword(s):

Last Glacial Maximum ◽

General Circulation ◽

Ice Sheets ◽

Ice Sheet ◽

Glacial Maximum ◽

Last Glacial ◽

Intercomparison Project ◽

The Last Glacial Maximum ◽

Random and externally controlled occurrence of Dansgaard-Oeschger events

10.5194/cp-2018-3 ◽

2018 ◽

Author(s):

Johannes Lohmann ◽

Peter D. Ditlevsen

Keyword(s):

General Circulation ◽

Statistical Hypothesis ◽

Boreal Summer ◽

Relative Distribution ◽

Event Sequence ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Abstract. Dansgaard-Oeschger (DO) events constitute the most pronounced mode of centennial to millennial climate variability of the last glacial period. Since their discovery, many decades of research have been devoted to understand the origin and nature of these rapid climate shifts. In recent years, a number of studies have appeared that report emergence of DO-type variability in fully coupled general circulation models via different mechanisms. These mechanisms result in the occurrence of DO events at varying degrees of regularity, ranging from periodic to random. When examining the full sequence of DO events as captured in the NGRIP ice core record, one can observe high irregularity in the timing of individual events at any stage within the last glacial period. In addition to the prevailing irregularity, certain properties of the DO event sequence, such as the average event frequency or the relative distribution of cold versus warm periods, appear to be changing throughout the glacial. By using statistical hypothesis tests on simple event models, we investigate whether the observed event sequence may have been generated by stationary random processes or rather has been strongly modulated by external factors. We find that the sequence of DO warming events is consistent with a stationary random process, whereas dividing the event sequence into warming and cooling events leads to inconsistency with two independent event processes. As we include external forcing, we find a particularly good fit to the observed DO sequence in a model where the average residence time in warm periods are controlled by global ice volume and cold periods by boreal summer insolation.

<i>δ</i><sup>13</sup>C decreases in the upper western South Atlantic during Heinrich Stadials 3 and 2

Climate of the Past ◽

10.5194/cp-13-345-2017 ◽

2017 ◽

Vol 13 (4) ◽

pp. 345-358 ◽

Cited By ~ 4

Author(s):

Marília C. Campos ◽

Cristiano M. Chiessi ◽

Ines Voigt ◽

Alberto R. Piola ◽

Henning Kuhnert ◽

...

Keyword(s):

Climate Change ◽

South Atlantic ◽

Meridional Overturning Circulation ◽

Glacial Period ◽

Last Deglaciation ◽

Last Glacial Period ◽

Last Glacial ◽

Change Events ◽

The Last Glacial ◽

Millennial Scale

Abstract. Abrupt millennial-scale climate change events of the last deglaciation (i.e. Heinrich Stadial 1 and the Younger Dryas) were accompanied by marked increases in atmospheric CO2 (CO2atm) and decreases in its stable carbon isotopic ratios (δ13C), i.e. δ13CO2atm, presumably due to outgassing from the ocean. However, information on the preceding Heinrich Stadials during the last glacial period is scarce. Here we present δ13C records from two species of planktonic foraminifera from the western South Atlantic that reveal major decreases (up to 1 ‰) during Heinrich Stadials 3 and 2. These δ13C decreases are most likely related to millennial-scale periods of weakening of the Atlantic meridional overturning circulation and the consequent increase (decrease) in CO2atm (δ13CO2atm). We hypothesise two mechanisms that could account for the decreases observed in our records, namely strengthening of Southern Ocean deep-water ventilation and weakening of the biological pump. Additionally, we suggest that air–sea gas exchange could have contributed to the observed δ13C decreases. Together with other lines of evidence, our data are consistent with the hypothesis that the CO2 added to the atmosphere during abrupt millennial-scale climate change events of the last glacial period also originated in the ocean and reached the atmosphere by outgassing. The temporal evolution of δ13C during Heinrich Stadials 3 and 2 in our records is characterized by two relative minima separated by a relative maximum. This w structure is also found in North Atlantic and South American records, further suggesting that such a structure is a pervasive feature of Heinrich Stadial 2 and, possibly, also Heinrich Stadial 3.

An ensemble of AMIP simulations with prescribed land surface temperatures

10.5194/gmd-2018-77 ◽

2018 ◽

Author(s):

Duncan Ackerley ◽

Robin Chadwick ◽

Dietmar Dommenget ◽

Paola Petrelli

Keyword(s):

Surface Temperature ◽

Land Surface ◽

General Circulation ◽

Global Climate ◽

Solar Constant ◽

Surface Temperatures ◽

Co2 Concentrations ◽

Land Surface Temperatures ◽

Intercomparison Project

Abstract. General circulation models (GCMs) are routinely run under Atmospheric Modelling Intercomparison Project (AMIP) conditions with prescribed sea surface temperatures (SSTs) and sea ice concentrations (SICs) from observations. These AMIP simulations are often used to evaluate the role of the land and/or atmosphere in causing the development of systematic errors in such GCMs. Extensions to the original AMIP experiment have also been developed to evaluate the response of the global climate to increased SSTs (prescribed) and carbon-dioxide (CO2) as part of the Cloud Feedback Model Intercomparison Project (CFMIP). None of these international modelling initiatives has undertaken a set of experiments where the land conditions are also prescribed, which is the focus of the work presented in this paper. Experiments are performed initially with freely varying land conditions (surface temperature and, soil temperature and mositure) under five different configurations (AMIP, AMIP with uniform 4 K added to SSTs, AMIP SST with quadrupled CO2, AMIP SST and quadrupled CO2 without the plant stomata response, and increasing the solar constant by 3.3 %). Then, the land surface temperatures from the free-land experiments are used to perform a set of “AMIP-prescribed land” (PL) simulations, which are evaluated against their free-land counterparts. The PL simulations agree well with the free-land experiments, which indicates that the land surface is prescribed in a way that is consistent with the original free-land configuration. Further experiments are also performed with different combinations of SSTs, CO2 concentrations, solar constant and land conditions. For example, SST and land conditions are used from the AMIP simulation with quadrupled CO2 in order to simulate the atmospheric response to increased CO2 concentrations without the surface temperature changing. The results of all these experiments have been made publicly available for further analysis. The main aims of this paper are to provide a description of the method used and an initial validation of these AMIP-prescribed land experiments.

Evaluation of the tail of the probability distribution of daily and sub-daily precipitation in CMIP6 models

Journal of Climate ◽

10.1175/jcli-d-20-0182.1 ◽

2021 ◽

pp. 1-61

Author(s):

Jesse Norris ◽

Alex Hall ◽

J. David Neelin ◽

Chad W. Thackeray ◽

Di Chen

Keyword(s):

General Circulation ◽

Daily Precipitation ◽

Precipitation Amount ◽

Coupled Model ◽

Lower Troposphere ◽

Intercomparison Project ◽

Cloud Tops ◽

The Tropics ◽

Fraction Models

AbstractDaily and sub-daily precipitation extremes in historical Coupled-Model-Intercomparison-Project-Phase-6 (CMIP6) simulations are evaluated against satellite-based observational estimates. Extremes are defined as the precipitation amount exceeded every x years, ranging from 0.01–10, encompassing the rarest events that are detectable in the observational record without noisy results. With increasing temporal resolution there is an increased discrepancy between models and observations: for daily extremes the multi-model median underestimates the highest percentiles by about a third, and for 3-hourly extremes by about 75% in the tropics. The novelty of the current study is that, to understand the model spread, we evaluate the 3-D structure of the atmosphere when extremes occur. In midlatitudes, where extremes are simulated predominantly explicitly, the intuitive relationship exists whereby higher-resolution models produce larger extremes (r=–0.49), via greater vertical velocity. In the tropics, the convective fraction (the fraction of precipitation simulated directly from the convective scheme) is more relevant. For models below 60% convective fraction, precipitation amount decreases with convective fraction (r=–0.63), but above 75% convective fraction, this relationship breaks down. In the lower-convective-fraction models, there is more moisture in the lower troposphere, closer to saturation. In the higher-convective-fraction models, there is deeper convection and higher cloud tops, which appears to be more physical. Thus, the low-convective models are mostly closer to the observations of extreme precipitation in the tropics, but likely for the wrong reasons. These inter-model differences in the environment in which extremes are simulated hold clues into how parameterizations could be modified in general circulation models to produce more credible 21st-Century projections.

Impact of circulation on tropical cloud feedbacks in cloud resolving models

10.5194/egusphere-egu21-2669 ◽

2021 ◽

Author(s):

Anna Mackie ◽

Michael P. Byrne

Keyword(s):

General Circulation ◽

Deep Convection ◽

Static Stability ◽

Cloud Feedback ◽

Dynamic Component ◽

Intercomparison Project ◽

Channel Configuration ◽

Open Question ◽

Long Channel

<div> <p>Uncertainty in the response of clouds to warming remains&#160;a significant&#160;barrier to reducing the range in projected&#160;climate sensitivity.&#160;A&#160;key&#160;question is to what extent cloud&#160;feedbacks&#160;can be attributed to changes in circulation, such as&#160;the strengthening or weakening of&#160;ascent&#160;or changes in the areas of&#160;convecting&#160;vs&#160;subsiding air.&#160;Previous research has shown that, in general circulation models (GCMs), the &#8216;dynamic&#8217; component of the cloud feedback &#8211; that which is due to changes in circulation rather than changes in the thermodynamic properties of clouds (Bony et al., 2006)&#160;&#8211;&#160;is&#160;generally small (Byrne and Schneider, 2018).&#160;An open question, however,&#160;is&#160;whether this&#160;extends to&#160;models at cloud resolving resolutions&#160;that explicitly simulate deep convection.&#160;&#160;</p> </div><div> <p>Here, we utilize simulations&#160;from&#160;the Radiative-Convective Equilibrium Model Intercomparison Project (RCEMIP, Wing et al., 2018, 2020)&#160;to quantify the&#160;impact of circulation on tropical cloud&#160;feedbacks.&#160;RCE&#160;is&#160;a&#160;simple&#160;idealisation&#160;of the tropical atmosphere&#160;and&#160;we&#160;focus on&#160;simulations&#160;in a long channel configuration&#160;with&#160;uniform sea surface temperatures&#160;of&#160;295, 300 and 305K.&#160;The dynamic component of the&#160;total cloud feedback is&#160;substantial&#160;for&#160;this&#160;suite of cloud resolving models (CRMs),&#160;and is driven by circulation changes&#160;and nonlinearity in the&#160;climatological&#160;relationship between clouds and circulation. The&#160;large spread&#160;in dynamic&#160;component&#160;across models&#160;is linked to&#160;the extent to which convection&#160;strengthens&#160;and narrows&#160;with&#160;warming.&#160;This strengthening/narrowing of convective regions&#160;is&#160;further&#160;linked to&#160;changes in&#160;clear-sky radiative cooling&#160;and mid-tropospheric static stability&#160;in subsiding regions.&#160;</p> </div><div> <p>&#160;</p> </div>

How cold was Europe at the Last Glacial Maximum? A synthesis of the progress achieved since the first PMIP model-data comparison

Climate of the Past ◽

10.5194/cp-3-331-2007 ◽

2007 ◽

Vol 3 (2) ◽

pp. 331-339 ◽

Cited By ~ 67

Author(s):

G. Ramstein ◽

M. Kageyama ◽

J. Guiot ◽

H. Wu ◽

C. Hély ◽

...

Keyword(s):

Last Glacial Maximum ◽

General Circulation ◽

Glacial Maximum ◽

Model Data ◽

Last Glacial ◽

Data Comparison ◽

The Last Glacial Maximum ◽

Winter Cooling ◽

Abstract. The Last Glacial Maximum has been one of the first foci of the Paleoclimate Modelling Intercomparison Project (PMIP). During its first phase, the results of 17 atmosphere general circulation models were compared to paleoclimate reconstructions. One of the largest discrepancies in the simulations was the systematic underestimation, by at least 10°C, of the winter cooling over Europe and the Mediterranean region observed in the pollen-based reconstructions. In this paper, we investigate the progress achieved to reduce this inconsistency through a large modelling effort and improved temperature reconstructions. We show that increased model spatial resolution does not significantly increase the simulated LGM winter cooling. Further, neither the inclusion of a vegetation cover compatible with the LGM climate, nor the interactions with the oceans simulated by the atmosphere-ocean general circulation models run in the second phase of PMIP result in a better agreement between models and data. Accounting for changes in interannual variability in the interpretation of the pollen data does not result in a reduction of the reconstructed cooling. The largest recent improvement in the model-data comparison has instead arisen from a new climate reconstruction based on inverse vegetation modelling, which explicitly accounts for the CO2 decrease at LGM and which substantially reduces the LGM winter cooling reconstructed from pollen assemblages. As a result, the simulated and observed LGM winter cooling over Western Europe and the Mediterranean area are now in much better agreement.