scholarly journals Climate Determinism Revisited: Multiple Equilibria in a Complex Climate Model

2011 ◽  
Vol 24 (4) ◽  
pp. 992-1012 ◽  
Author(s):  
David Ferreira ◽  
John Marshall ◽  
Brian Rose
Keyword(s):  
Energy Balance ◽  
Sea Ice ◽  
Heat Transport ◽  
Ocean Circulation ◽  
General Circulation ◽  
Multiple Equilibria ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Ocean Heat Transport ◽  
Ice Cap

Abstract Multiple equilibria in a coupled ocean–atmosphere–sea ice general circulation model (GCM) of an aquaplanet with many degrees of freedom are studied. Three different stable states are found for exactly the same set of parameters and external forcings: a cold state in which a polar sea ice cap extends into the midlatitudes; a warm state, which is ice free; and a completely sea ice–covered “snowball” state. Although low-order energy balance models of the climate are known to exhibit intransitivity (i.e., more than one climate state for a given set of governing equations), the results reported here are the first to demonstrate that this is a property of a complex coupled climate model with a consistent set of equations representing the 3D dynamics of the ocean and atmosphere. The coupled model notably includes atmospheric synoptic systems, large-scale circulation of the ocean, a fully active hydrological cycle, sea ice, and a seasonal cycle. There are no flux adjustments, with the system being solely forced by incoming solar radiation at the top of the atmosphere. It is demonstrated that the multiple equilibria owe their existence to the presence of meridional structure in ocean heat transport: namely, a large heat transport out of the tropics and a relatively weak high-latitude transport. The associated large midlatitude convergence of ocean heat transport leads to a preferred latitude at which the sea ice edge can rest. The mechanism operates in two very different ocean circulation regimes, suggesting that the stabilization of the large ice cap could be a robust feature of the climate system. Finally, the role of ocean heat convergence in permitting multiple equilibria is further explored in simpler models: an atmospheric GCM coupled to a slab mixed layer ocean and an energy balance model.

scholarly journals Interhemispheric Asymmetry of Warming in an Eddy-Permitting Coupled Sector Model

2015 ◽  
Vol 28 (18) ◽  
pp. 7385-7406 ◽  
Author(s):  
David K. Hutchinson ◽  
Matthew H. England ◽  
Andrew M. Hogg ◽  
Kate Snow
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
Ocean Circulation ◽  
High Latitude ◽  
Climate Model ◽  
Mean Flow ◽  
Surface Warming ◽  
Sector Model ◽  
Air Temperatures ◽  
Wide Sector

Abstract Climate model projections and observations show a faster rate of warming in the Northern Hemisphere (NH) than the Southern Hemisphere (SH). This asymmetry is partly due to faster rates of warming over the land than the ocean, and partly due to the ocean circulation redistributing heat toward the NH. This study examines the interhemispheric warming asymmetry in an intermediate complexity coupled climate model with eddy-permitting (0.25°) ocean resolution, and results are compared with a similar model with coarse (1°) ocean resolution. The models use a pole-to-pole 60° wide sector domain in the ocean and a 120° wide sector in the atmosphere, with Atlantic-like bathymetry and a simple land model. There is a larger high-latitude ocean temperature asymmetry in the 0.25° model compared with the 1° model, both in equilibrated control runs and in response to greenhouse warming. The larger warming asymmetry is caused by greater melting of NH sea ice in the 0.25° model, associated with faster, less viscous boundary currents transporting heat northward. The SH sea ice and heat transport response is relatively insensitive to the resolution change, since the eddy heat transport differences between the models are small compared with the mean flow heat transport. When a wind shift and intensification is applied in these warming scenarios, the warming asymmetry is further enhanced, with greater upwelling of cool water in the Southern Ocean and enhanced warming in the NH. Surface air temperatures show a substantial but lesser degree of high-latitude warming asymmetry, reflecting the sea surface warming patterns over the ocean but warming more symmetrically over the land regions.

scholarly journals Relations between Northward Ocean and Atmosphere Energy Transports in a Coupled Climate Model

2008 ◽  
Vol 21 (3) ◽  
pp. 561-575 ◽  
Author(s):  
Michael Vellinga ◽  
Peili Wu
Keyword(s):  
Heat Transport ◽  
General Circulation ◽  
Energy Transport ◽  
Climate Model ◽  
Atmospheric Transport ◽  
Circulation Model ◽  
Meridional Overturning Circulation ◽  
Ocean Heat Transport ◽  
Poleward Heat Transport ◽  
Low Latitudes

Abstract The Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) is used to analyze the relation between northward energy transports in the ocean and atmosphere at centennial time scales. In a transient water-hosing experiment, where suppressing the Atlantic meridional overturning circulation (MOC) causes a reduction in northward ocean heat transport of up to 0.75 PW (i.e., 75%), the atmosphere compensates by increasing its northward transport of moist static energy. This compensation is very efficient at low latitudes and near complete at the equator throughout the experiment, but is incomplete farther north across the northern midlatitude storm tracks. The change in atmosphere energy transport enables the model to find a new global-mean radiative equilibrium after 240 yr. In a perturbed physics ensemble of HadCM3 it was found that time-averaged meridional energy transports in ocean and atmosphere can act opposingly. Where model formulation causes an unbalanced mean climate state, for example, an excessive top-of-the-atmosphere radiative surplus at low latitudes, the atmosphere increases its poleward energy transport to disperse this excess. MOC and ocean poleward heat transport tend to be reduced in such model versions, and this offsets the increased poleward atmospheric transport of the low-latitude energy surplus. Model versions that are close to net radiative equilibrium also have ocean heat transport and MOC close to observed values.

Interactions between ocean heat transport and Arctic sea ice

2020 ◽  
Author(s):  
David Docquier ◽  
Ramon Fuentes-Franco ◽  
Klaus Wyser ◽  
Torben Koenigk
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Arctic Sea Ice ◽  
Ocean Heat Transport ◽  
Arctic Sea ◽  
Fast Pace ◽  
Area And Volume

<p>Arctic sea ice has been retreating at fast pace in the last decades, with potential impacts on the weather and climate at mid and high latitudes, as well as the biosphere and society. Sea-ice loss is driven by anthropogenic global warming, atmospheric circulation changes, climate feedbacks, and ocean heat transport. To date, no clear consensus regarding the detailed impact of ocean heat transport on Arctic sea ice exists. Previous observational and modeling studies show that the poleward Atlantic Ocean heat transport and Arctic sea-ice area and volume are generally anti-correlated, suggesting a decrease in sea-ice area and volume with larger ocean heat transport. In turn, the changing sea ice may also affect ocean heat transport, but this effect has been much less studied. Our study explores the two-way interactions between ocean heat transport and Arctic sea ice. We use the EC-Earth global climate model, coupling the atmosphere and ocean, and perform different sensitivity experiments to gain insights into these interactions. The mechanisms by which ocean heat transport and Arctic sea ice interact are analyzed, and compared to observations. This study provides a way to better constrain model projections of Arctic sea ice, based on the relationships between ocean heat transport and Arctic sea ice.</p>

scholarly journals Ocean Heat Transport, Sea Ice, and Multiple Climate States: Insights from Energy Balance Models

2009 ◽  
Vol 66 (9) ◽  
pp. 2828-2843 ◽  
Author(s):  
Brian E. J. Rose ◽  
John Marshall
Keyword(s):  
Energy Balance ◽  
Sea Ice ◽  
Heat Transport ◽  
Wind Stress ◽  
Ocean Heat Transport ◽  
Meridional Transport ◽  
Meridional Heat Transport ◽  
Ocean Gyres ◽  
Ice Edge ◽  
Energy Balance Models

Abstract Several extensions of energy balance models (EBMs) are explored in which (i) sea ice acts to insulate the atmosphere from the ocean and (ii) ocean heat transport is allowed to have some meridional structure controlled by the wind, with minima at which the ice edge can rest. These new models support multiple stable ice edges not found in the classical EBM and a hysteresis loop capable of generating abrupt warming as the ice edge “jumps” from mid- to high latitudes. The new equilibria are demonstrated in two classes of model, in which the wind stress is either specified externally or generated interactively. Wind stress is computed by introducing a dynamical constraint into the EBM to represent the simultaneous meridional transport of energy and angular momentum in the atmosphere. This wind stress is used to drive ocean gyres, with associated structure in their meridional heat transport, so that the atmosphere and ocean are coupled together both thermally and mechanically.

scholarly journals Ocean Heat Transport as a Cause for Model Uncertainty in Projected Arctic Warming

2011 ◽  
Vol 24 (5) ◽  
pp. 1451-1460 ◽  
Author(s):  
Irina Mahlstein ◽  
Reto Knutti
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
General Circulation ◽  
General Circulation Models ◽  
Arctic Sea Ice ◽  
The Arctic ◽  
Ocean Heat Transport ◽  
Sea Ice Extent ◽  
Arctic Sea ◽  
Future Warming

Abstract The Arctic climate is governed by complex interactions and feedback mechanisms between the atmosphere, ocean, and solar radiation. One of its characteristic features, the Arctic sea ice, is very vulnerable to anthropogenically caused warming. Production and melting of sea ice is influenced by several physical processes. The authors show that the northward ocean heat transport is an important factor in the simulation of the sea ice extent in the current general circulation models. Those models that transport more energy to the Arctic show a stronger future warming, in the Arctic as well as globally. Larger heat transport to the Arctic, in particular in the Barents Sea, reduces the sea ice cover in this area. More radiation is then absorbed during summer months and is radiated back to the atmosphere in winter months. This process leads to an increase in the surface temperature and therefore to a stronger polar amplification. The models that show a larger global warming agree better with the observed sea ice extent in the Arctic. In general, these models also have a higher spatial resolution. These results suggest that higher resolution and greater complexity are beneficial in simulating the processes relevant in the Arctic and that future warming in the high northern latitudes is likely to be near the upper range of model projections, consistent with recent evidence that many climate models underestimate Arctic sea ice decline.

scholarly journals Decadal variability in high northern latitudes as simulated by an intermediate-complexity climate model

2001 ◽  
Vol 33 ◽  
pp. 525-532 ◽  
Author(s):  
H. Goosse ◽  
F. M. Selten ◽  
R. J. Haarsma ◽  
J. D. Opsteegh
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Model Comparison ◽  
Climate Model ◽  
Decadal Variability ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
The Arctic ◽  
Intermediate Complexity ◽  
Northern Latitudes

AbstractA 2500 year integration has been performed with a global coupled atmospheric-sea-ice-ocean model of intermediate complexity with the main objective of studying the climate variability in polar regions on decadal time-scales and longer. The atmospheric component is the ECBILT model, a spectral T21 three-level quasi-geostrophic model that includes a representation of horizontal and vertical heat transfers as well as of the hydrological cycle. ECBILT is coupled to the CLIO model, which consists of a primitive-equation free-surface ocean general circulation model and a dynamic-thermodynamic sea-ice model. Comparison of model results with observations shows that the ECBILT-CLIO model is able to reproduce reasonably well the climate of the high northern latitudes. The dominant mode of coupled variability between the atmospheric circulation and sea-ice cover in the simulation consists of an annular mode for geopotential height at 800 hPa and of a dipole between the Barents and Labrador Seas for the sea-ice concentration which are similar to observed patterns of variability. In addition, the simulation displays strong decadal variability in the sea-ice volume, with a significant peak at about 18 years. Positive volume anomalies are caused by (1) a decrease in ice export through Fram Strait associated with more anticyclonic winds at high latitudes, (2) modifications in the freezing/melting rates in the Arctic due to lower air temperature and higher surface albedo, and (3) a weaker heat flux at the ice base in the Barents and Kara seas caused by a lower inflow of warm Atlantic water. Opposite anomalies occur during the volume-decrease phase of the oscillation.

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

2012 ◽  
Vol 8 (6) ◽  
pp. 2079-2092 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
General Circulation ◽  
Climate Models ◽  
Ice Cover ◽  
The State ◽  
Snowball Earth ◽  
Ocean Heat Transport ◽  
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 study the effect of bare sea-ice albedo, sea-ice dynamics and ocean heat transport on (CO2, SI)* in the atmosphere–ocean general circulation model ECHAM5/MPI-OM with Marinoan (~ 635 Ma) continents and solar insolation (94% of modern). In its standard setup, ECHAM5/MPI-OM initiates a~Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Replacing 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%). This is consistent with previous work and results from net evaporation and local melting near the sea-ice margin. 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 hundred times lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, the simulation of sea-ice dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO2 for Snowball initiation relative to other models. Ocean heat transport has no effect on the critical sea-ice cover and only slightly decreases 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 indication of the Jormungand bifurcation and hysteresis in ECHAM5/MPI-OM. The state with 85% sea-ice cover therefore is a soft Snowball state rather than a true Jormungand state. Overall, our results demonstrate that differences in sea-ice dynamics schemes can be at least as important as differences in sea-ice albedo for causing the spread in climate models' estimates of the Snowball Earth bifurcation. A detailed understanding of Snowball Earth initiation therefore requires future research on sea-ice dynamics to determine which model's simulation is most realistic.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

scholarly journals Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model

2015 ◽  
Vol 15 (10) ◽  
pp. 5537-5555 ◽  
Author(s):  
R. Eichinger ◽  
P. Jöckel ◽  
S. Brinkop ◽  
M. Werner ◽  
S. Lossow
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
General Circulation ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Isotope Ratios ◽  
Physical Fractionation ◽  
Water Isotopologues ◽  
Stratospheric Water Vapour

Abstract. This modelling study aims at an improved understanding of the processes that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. An additional (and separate from the actual) hydrological cycle has been introduced into the chemistry–climate model EMAC, including the water isotopologues HDO and H218O and their physical fractionation processes. Additionally an explicit computation of the contribution of methane oxidation to H2O and HDO has been incorporated. The model expansions allow detailed analyses of water vapour and its isotope ratio with respect to deuterium throughout the stratosphere and in the transition region to the troposphere. In order to assure the correct representation of the water isotopologues in the model's hydrological cycle, the expanded system has been evaluated in several steps. The physical fractionation effects have been evaluated by comparison of the simulated isotopic composition of precipitation with measurements from a ground-based network (GNIP) and with the results from the isotopologue-enabled general circulation model ECHAM5-wiso. The model's representation of the chemical HDO precursor CH3D in the stratosphere has been confirmed by a comparison with chemical transport models (1-D, CHEM2D) and measurements from radiosonde flights. Finally, the simulated stratospheric HDO and the isotopic composition of water vapour have been evaluated, with respect to retrievals from three different satellite instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric water vapour isotope ratios between two of the three satellite retrievals can now partly be explained.

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