scholarly journals Influence of Surface Topography on the Critical Carbon Dioxide Level Required for the Formation of a Modern Snowball Earth

2018 ◽  
Vol 31 (20) ◽  
pp. 8463-8479 ◽  
Author(s):  
Yonggang Liu ◽  
W. Richard Peltier ◽  
Jun Yang ◽  
Yongyun Hu
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
Land Surface ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Snowball Earth ◽  
Ice Dynamics

The influence of continental topography on the initiation of a global glaciation (i.e., snowball Earth) is studied with both a fully coupled atmosphere–ocean general circulation model (AOGCM), CCSM3, and an atmospheric general circulation model (AGCM), CAM3 coupled to a slab ocean model. It is found that when the climate is very cold, snow cover over the central region of the Eurasian continent decreases when the atmospheric CO2 concentration ( pCO2) is reduced. In the coupled model, this constitutes a negative feedback due to the reduction of land surface albedo that counteracts the positive feedback due to sea ice expansion toward the equator. When the solar insolation is 94% of the present-day value, Earth enters a snowball state when pCO2 is ~35 ppmv. On the other hand, if the continents are assumed to be flat topographically (with the global mean elevation as in the more realistic present-day case), Earth enters a snowball state more easily at pCO2 = ~60 ppmv. Therefore, the presence of topography may increase the stability of Earth against descent into a snowball state. On the contrary, a snowball Earth is found to form much more easily when complex topography is present than when it is not in CAM3. This happens despite the fact that the mid- to high-latitude climate is much warmer (by ~10°C) when topography is present than when it is not. Analyses show that neglecting sea ice dynamics in this model prevents the warming anomaly in the mid- to high latitudes from being efficiently transmitted into the tropics.

scholarly journals Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins

2012 ◽  
Vol 8 (4) ◽  
pp. 2445-2475 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Ice Cover ◽  
Ocean General Circulation Model ◽  
Snowball Earth ◽  
Ice Dynamics ◽  
Sea Ice Dynamics

Abstract. The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we revisit the initiation of a Snowball Earth in the atmosphere-ocean general circulation model ECHAM5/MPI-OM for Marinoan (~630 Ma) continents and solar insolation decreased to 94%. In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Previous work has shown that the Snowball Earth bifurcation can be pushed equatorward if a low bare sea ice albedo is assumed because bare sea ice is exposed by net evaporation in the descent region of the Hadley circulation. Consistent with this, when we replace the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a much lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, both lowering the bare sea-ice albedo and disabling sea-ice dynamics increase the critical sea-ice cover in ECHAM5/MPI-OM, but sea-ice dynamics have a much larger influence on the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no Jormungand bifurcation between this Jormungand-like state and states with mid-latitude sea-ice margins. Our results indicate that differences in sea-ice dynamics schemes can be as important as sea ice albedo for causing the spread in climate model's estimates of the location of the Snowball Earth bifurcation.

scholarly journals The Finite Element Sea ice-Ocean Model (FESOM): formulation of an unstructured-mesh ocean general circulation model

2013 ◽  
Vol 6 (3) ◽  
pp. 3893-3976 ◽  
Author(s):  
Q. Wang ◽  
S. Danilov ◽  
D. Sidorenko ◽  
R. Timmermann ◽  
C. Wekerle ◽  
...  
Keyword(s):  
Finite Element ◽  
Sea Ice ◽  
General Circulation Model ◽  
General Circulation ◽  
Unstructured Mesh ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Climate Modelling ◽  
Ocean General Circulation

Abstract. The Finite Element Sea ice-Ocean Model (FESOM) is the first global ocean general circulation model based on unstructured-mesh methods that has been developed for the purpose of climate research. The advantage of unstructured-mesh models is their flexible multi-resolution modelling functionality. In this study, an overview of the main features of FESOM will be given; based on sensitivity experiments a number of specific parameter choices will be explained; and directions of future developments will be outlined. It is argued that FESOM is sufficiently mature to explore the benefits of multi-resolution climate modelling and that it provides an excellent platform for further developments required to advance the field of climate modelling on unstructured meshes.

scholarly journals The Finite Element Sea Ice-Ocean Model (FESOM) v.1.4: formulation of an ocean general circulation model

2014 ◽  
Vol 7 (2) ◽  
pp. 663-693 ◽  
Author(s):  
Q. Wang ◽  
S. Danilov ◽  
D. Sidorenko ◽  
R. Timmermann ◽  
C. Wekerle ◽  
...  
Keyword(s):  
Finite Element ◽  
Sea Ice ◽  
General Circulation Model ◽  
General Circulation ◽  
Unstructured Mesh ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Climate Modelling ◽  
Ocean General Circulation

Abstract. The Finite Element Sea Ice-Ocean Model (FESOM) is the first global ocean general circulation model based on unstructured-mesh methods that has been developed for the purpose of climate research. The advantage of unstructured-mesh models is their flexible multi-resolution modelling functionality. In this study, an overview of the main features of FESOM will be given; based on sensitivity experiments a number of specific parameter choices will be explained; and directions of future developments will be outlined. It is argued that FESOM is sufficiently mature to explore the benefits of multi-resolution climate modelling and that its applications will provide information useful for the advancement of climate modelling on unstructured meshes.

scholarly journals Initiation of a Marinoan Snowball Earth in a state-of-the-art atmosphere-ocean general circulation model

2011 ◽  
Vol 7 (1) ◽  
pp. 249-263 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot ◽  
R. T. Pierrehumbert ◽  
J. Marotzke
Keyword(s):  
Sea Ice ◽  
Bifurcation Point ◽  
General Circulation ◽  
State Of The Art ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Snowball Earth ◽  
Surface Boundary ◽  
Surface Boundary Conditions ◽  
Global Mean

Abstract. We study the initiation of a Marinoan Snowball Earth (~635 million years before present) with the state-of-the-art atmosphere-ocean general circulation model ECHAM5/MPI-OM. This is the most sophisticated model ever applied to Snowball initiation. A comparison with a pre-industrial control climate shows that the change of surface boundary conditions from present-day to Marinoan, including a shift of continents to low latitudes, induces a global-mean cooling of 4.6 K. Two thirds of this cooling can be attributed to increased planetary albedo, the remaining one third to a weaker greenhouse effect. The Marinoan Snowball Earth bifurcation point for pre-industrial atmospheric carbon dioxide is between 95.5 and 96% of the present-day total solar irradiance (TSI), whereas a previous study with the same model found that it was between 91 and 94% for present-day surface boundary conditions. A Snowball Earth for TSI set to its Marinoan value (94% of the present-day TSI) is prevented by doubling carbon dioxide with respect to its pre-industrial level. A zero-dimensional energy balance model is used to predict the Snowball Earth bifurcation point from only the equilibrium global-mean ocean potential temperature for present-day TSI. We do not find stable states with sea-ice cover above 55%, and land conditions are such that glaciers could not grow with sea-ice cover of 55%. Therefore, none of our simulations qualifies as a "slushball" solution. While uncertainties in important processes and parameters such as clouds and sea-ice albedo suggest that the Snowball Earth bifurcation point differs between climate models, our results contradict previous findings that Snowball Earth initiation would require much stronger forcings.

scholarly journals The CSIRO Mk3L climate system model version 1.0 – Part 1: Description and evaluation

2011 ◽  
Vol 4 (2) ◽  
pp. 483-509 ◽  
Author(s):  
S. J. Phipps ◽  
L. D. Rotstayn ◽  
H. B. Gordon ◽  
J. L. Roberts ◽  
A. C. Hirst ◽  
...  
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
Land Surface ◽  
General Circulation ◽  
Regional Scale ◽  
Circulation Model ◽  
Climate System ◽  
System Model ◽  
Desktop Computer ◽  
Climate System Model

Abstract. The CSIRO Mk3L climate system model is a coupled general circulation model, designed primarily for millennial-scale climate simulations and palaeoclimate research. Mk3L includes components which describe the atmosphere, ocean, sea ice and land surface, and combines computational efficiency with a stable and realistic control climatology. This paper describes the model physics and software, analyses the control climatology, and evaluates the ability of the model to simulate the modern climate. Mk3L incorporates a spectral atmospheric general circulation model, a z-coordinate ocean general circulation model, a dynamic-thermodynamic sea ice model and a land surface scheme with static vegetation. The source code is highly portable, and has no dependence upon proprietary software. The model distribution is freely available to the research community. A 1000-yr climate simulation can be completed in around one-and-a-half months on a typical desktop computer, with greater throughput being possible on high-performance computing facilities. Mk3L produces realistic simulations of the larger-scale features of the modern climate, although with some biases on the regional scale. The model also produces reasonable representations of the leading modes of internal climate variability in both the tropics and extratropics. The control state of the model exhibits a high degree of stability, with only a weak cooling trend on millennial timescales. Ongoing development work aims to improve the model climatology and transform Mk3L into a comprehensive earth system model.

scholarly journals Ocean-sea-ice coupling in a global ocean general circulation model

1997 ◽  
Vol 25 ◽  
pp. 116-120 ◽  
Author(s):  
S. Legutke ◽  
E. Maier-Reimkr ◽  
A. Stössel ◽  
A. Hellbach
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
Ocean Circulation ◽  
General Circulation ◽  
Circulation Model ◽  
Ice Cover ◽  
Ocean General Circulation Model ◽  
Global Ocean ◽  
Ocean General Circulation ◽  
The Impact

A global ocean general circulation model has been coupled with a dynamic thermodynamic sea-ice model. This model has been spun-up in a 1000 year integration using daily atmosphere model data. Main water masses and currents are reproduced as well as the seasonal characteristics of the ice cover of the Northern and Southern Hemispheres. Model results for the Southern Ocean, however, show the ice cover as too thin, and there are large permanent polynyas in the Weddell and Ross Seas. These polynyas are due to a large upward oceanic heat flux caused by haline rejection during the freezing of sea ice. Sensitivity studies were performed to test several ways of treating the sea-surface salinity and the rejected brine. The impact on the ice cover, water-mass characteristics, and ocean circulation are described.

scholarly journals FORTE 2.0: a fast, parallel and flexible coupled climate model

2021 ◽  
Vol 14 (1) ◽  
pp. 275-293
Author(s):  
Adam T. Blaker ◽  
Manoj Joshi ◽  
Bablu Sinha ◽  
David P. Stevens ◽  
Robin S. Smith ◽  
...  
Keyword(s):  
General Circulation Model ◽  
General Circulation ◽  
Climate Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
Coupled Climate Model ◽  
Layer Depth ◽  
Ocean General Circulation ◽  
Modular Ocean Model

Abstract. FORTE 2.0 is an intermediate-resolution coupled atmosphere–ocean general circulation model (AOGCM) consisting of the Intermediate General Circulation Model 4 (IGCM4), a T42 spectral atmosphere with 35σ layers, coupled to Modular Ocean Model – Array (MOMA), a 2∘ × 2∘ ocean with 15 z-layer depth levels. Sea ice is represented by a simple flux barrier. Both the atmosphere and ocean components are coded in Fortran. It is capable of producing a stable climate for long integrations without the need for flux adjustments. One flexibility afforded by the IGCM4 atmosphere is the ability to configure the atmosphere with either 35σ layers (troposphere and stratosphere) or 20σ layers (troposphere only). This enables experimental designs for exploring the roles of the troposphere and stratosphere, and the faster integration of the 20σ layer configuration enables longer duration studies on modest hardware. A description of FORTE 2.0 is given, followed by the analysis of two 2000-year control integrations, one using the 35σ configuration of IGCM4 and one using the 20σ configuration.

Ocean dynamics and climate during a Neoproterozoic snowball Earth and its aftermath as simulated in a coupled Earth system model

2020 ◽  
Author(s):  
Lennart Ramme ◽  
Jochem Marotzke
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Cold Climate ◽  
Ocean Dynamics ◽  
Snowball Earth ◽  
Ice Melt ◽  
Ocean Surface Currents ◽  
Before And After

<p>The Neoproterozoic glaciations, referred to as snowball Earth periods, describe the most extreme transition from a very cold climate to a state of strong greenhouse effect. Atmospheric CO<sub>2</sub> concentrations are rising during the snowball, due to the shutdown of oceanic and terrestrial carbon sinks, until a tipping point is reached and a rapid deglaciation sets in. Subsequently, a warm and completely ice-free climate under very high CO<sub>2</sub> concentrations develops. We show first results of simulations using a coupled atmosphere-ocean general circulation model covering the initiation, as well as the melting of the Marinoan snowball Earth (645 – 635 My ago) and the greenhouse climate in its aftermath. CO<sub>2</sub> concentrations are decreased to initiate a global glaciation and then increased again in order to melt the snowball Earth. As soon as a certain CO<sub>2</sub> threshold is reached, sea-ice melts rapidly, reaching a completely ice-free ocean after only one hundred years, in our model without land glaciers. The ocean becomes strongly stratified, because at the surface the freshwater from the sea-ice melt is warming up quickly, whereas the deeper ocean remains cold and salty. Ocean surface currents return to their pre-snowball behavior soon after the melt, but destratification is slow. The largest mixed layer depths of up to 500 m are reached in the mid latitudes of the winter hemisphere. We compare the climate before and after the snowball state and estimate the time needed for destratification.</p>

scholarly journals Coupled Climate Simulation by Constraining Ocean Fields in a Coupled Model with Ocean Data

2009 ◽  
Vol 22 (20) ◽  
pp. 5541-5557 ◽  
Author(s):  
Yosuke Fujii ◽  
Toshiyuki Nakaegawa ◽  
Satoshi Matsumoto ◽  
Tamaki Yasuda ◽  
Goro Yamanaka ◽  
...  
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
The Philippines ◽  
Ocean Model ◽  
Climate Simulation ◽  
Philippine Sea ◽  
Estimation System

Abstract The authors developed a system for simulating climate variation by constraining the ocean component of a coupled atmosphere–ocean general circulation model (CGCM) through ocean data assimilation and conducted a climate simulation [Multivariate Ocean Variational Estimation System–Coupled Version Reanalysis (MOVE-C RA)]. The monthly variation of sea surface temperature (SST) is reasonably recovered in MOVE-C RA. Furthermore, MOVE-C RA has improved precipitation fields over the Atmospheric Model Intercomparison Project (AMIP) run (a simulation of the atmosphere model forced by observed daily SST) and the CGCM free simulation run. In particular, precipitation in the Philippine Sea in summer is improved over the AMIP run. This improvement is assumed to stem from the reproduction of the interaction between SST and precipitation, indicated by the lag of the precipitation change behind SST. Enhanced (suppressed) convection tends to induce an SST drop (rise) because of cloud cover and ocean mixing in the real world. A lack of this interaction in the AMIP run leads to overestimating the precipitation in the Bay of Bengal in summer. Because it is recovered in MOVE-C RA, the overestimate is suppressed. This intensifies the zonal Walker circulation and the monsoon trough, resulting in enhanced convection in the Philippine Sea. The spurious positive correlation between SST and precipitation around the Philippines in the AMIP run in summer is also removed in MOVE-C RA. These improvements demonstrate the effectiveness of simulating ocean interior processes with the ocean model and data assimilation for reproducing the climate variability.

scholarly journals Retrospective Forecasts of Interannual Sea Surface Temperature Anomalies from 1982 to Present Using a Directly Coupled Atmosphere–Ocean General Circulation Model

2005 ◽  
Vol 133 (10) ◽  
pp. 2972-2995 ◽  
Author(s):  
David G. DeWitt
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
General Circulation Model ◽  
General Circulation ◽  
Coupled Model ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Sea Surface ◽  
Initial Condition ◽  
Ocean General Circulation

Abstract A large number of ensemble hindcasts (or retrospective forecasts) of tropical Pacific sea surface temperature (SST) have been made with a coupled atmosphere–ocean general circulation model (CGCM) that does not employ flux correction in order to evaluate the potential skill of the model as a seasonal forecasting tool. Oceanic initial conditions are provided by an ocean data assimilation system. Ensembles of seven forecasts of 6-month length are made starting each month in the 1982 to 2002 period. Skill of the coupled model is evaluated from both a deterministic and a probabilistic perspective. The skill metrics are calculated using both the bulk method, which includes all initial condition months together, and as a function of initial condition month. The latter method allows a more objective evaluation of how the model has performed in the context in which forecasts are actually made and applied. The deterministic metrics used are the anomaly correlation and the root-mean-square error. The coupled model deterministic skill metrics are compared with those from persistence and damped persistence reference forecasts. Despite the fact that the coupled model has a large cold bias in the central and eastern equatorial Pacific this coupled model is shown to have forecast skill that is competitive with other state-of-the-art forecasting techniques. Potential skill from probabilistic forecasts made using the coupled model ensemble members are evaluated using the relative operating characteristics method. This analysis indicates that for most initial condition months this coupled model has more skill at forecasting cold events than warm or neutral events in the central Pacific. In common with other forecasting systems, the coupled model forecast skill is found to be lowest for forecasts passing through the Northern Hemisphere (NH) spring. Diagnostics of this so-called spring predictability barrier in the context of this coupled model indicate that two factors likely contribute to this predictability barrier. First, the coupled model shows a too-weak coupling of the surface and subsurface temperature anomalies during NH spring. Second, the coupled-model-simulated signal-to-noise ratio for SST anomalies is much lower during NH spring than at other times of the year, indicating that the model’s potential predictability is low at this time.

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