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See detailDescription of the Earth system model of intermediate complexity LOVECLIM version 1.2
Goosse, H.; Brovkin, V.; Fichefet, T. et al

in Geoscientific Model Development (2010), 3(2), 603-633

The main characteristics of the new version 1.2 of the three-dimensional Earth system model of intermediate complexity LOVECLIM are briefly described. LOVECLIM 1.2 includes representations of the ... [more ▼]

The main characteristics of the new version 1.2 of the three-dimensional Earth system model of intermediate complexity LOVECLIM are briefly described. LOVECLIM 1.2 includes representations of the atmosphere, the ocean and sea ice, the land surface (including vegetation), the ice sheets, the icebergs and the carbon cycle. The atmospheric component is ECBilt2, a T21, 3-level quasi-geostrophic model. The ocean component is CLIO3, which consists of an ocean general circulation model coupled to a comprehensive thermodynamic-dynamic sea-ice model. Its horizontal resolution is of 3° by 3°, and there are 20 levels in the ocean. ECBilt-CLIO is coupled to VECODE, a vegetation model that simulates the dynamics of two main terrestrial plant functional types, trees and grasses, as well as desert. VECODE also simulates the evolution of the carbon cycle over land while the ocean carbon cycle is represented by LOCH, a comprehensive model that takes into account both the solubility and biological pumps. The ice sheet component AGISM is made up of a three-dimensional thermomechanical model of the ice sheet flow, a visco-elastic bedrock model and a model of the mass balance at the ice-atmosphere and ice-ocean interfaces. For both the Greenland and Antarctic ice sheets, calculations are made on a 10 km by 10 km resolution grid with 31 sigma levels. LOVECLIM1.2 reproduces well the major characteristics of the observed climate both for present-day conditions and for key past periods such as the last millennium, the mid-Holocene and the Last Glacial Maximum. However, despite some improvements compared to earlier versions, some biases are still present in the model. The most serious ones are mainly located at low latitudes with an overestimation of the temperature there, a too symmetric distribution of precipitation between the two hemispheres, and an overestimation of precipitation and vegetation cover in the subtropics. In addition, the atmospheric circulation is too weak. The model also tends to underestimate the surface temperature changes (mainly at low latitudes) and to overestimate the ocean heat uptake observed over the last decades. [less ▲]

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See detailDeep Water Formation in the North Pacific during the Last Glacial Termination
Okazaki, Y.; Timmermann, A.; Menviel, L. et al

in Science (2010), 329

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See detailThe mechanism behind internally generated centennial-to-millennial scale climate variability in an earth system model of intermediate complexity
Friedrich, T.; Timmermann, A.; Menviel, L. et al

in Geoscientific Model Development (2010), 3(2), 377--389

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See detailModel sensitivities and carbon cycle - climate feedbacks: a study with an Earth System Model
Mouchet, Anne ULg; Loutre, M. F.; Goelzer, H. et al

Poster (2009, November)

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See detailBiogeochemical changes in the North Pacific in response to a shut down of the Atlantic meridional overturning
Menviel, L.; Timmermann, A.; Timm, O. et al

Conference (2009, May)

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See detailAssessing the World Ocean ventilation timescales with simple analogs - the leaky funnel model
Mouchet, Anne ULg; Deleersnijder, Eric

Conference (2009, February)

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See detailAssessment of modelling uncertainties in long-term climate and sea level change projections "Aster"
Fichefet, T.; Loutre, M.-F.; Goosse, H. et al

Report (2009)

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See detailOceanic sources, sinks, and transport of atmospheric CO2
Gruber, Nicolas; Gloor, Manuel; Fletcher, Sara E Mikaloff et al

in Global Biogeochemical Cycles (2009), 23

We synthesize estimates of the contemporary net air-sea CO2 flux on the basis of an inversion of interior ocean carbon observations using a suite of 10 ocean general circulation models (Mikaloff Fletcher ... [more ▼]

We synthesize estimates of the contemporary net air-sea CO2 flux on the basis of an inversion of interior ocean carbon observations using a suite of 10 ocean general circulation models (Mikaloff Fletcher et al., 2006, 2007) and compare them to estimates based on a new climatology of the air-sea difference of the partial pressure of CO2 (pCO(2)) (Takahashi et al., 2008). These two independent flux estimates reveal a consistent description of the regional distribution of annual mean sources and sinks of atmospheric CO2 for the decade of the 1990s and the early 2000s with differences at the regional level of generally less than 0.1 Pg C a(-1). This distribution is characterized by outgassing in the tropics, uptake in midlatitudes, and comparatively small fluxes in the high latitudes. Both estimates point toward a small(similar to -0.3 Pg C a(-1)) contemporary CO2 sink in the Southern Ocean (south of 44 degrees S), a result of the near cancellation between a substantial outgassing of natural CO2 and a strong uptake of anthropogenic CO2. A notable exception in the generally good agreement between the two estimates exists within the Southern Ocean: the ocean inversion suggests a relatively uniform uptake, while the pCO(2)-based estimate suggests strong uptake in the region between 58 degrees S and 44 degrees S, and a source in the region south of 58 degrees S. Globally and for a nominal period between 1995 and 2000, the contemporary net air-sea flux of CO2 is estimated to be -1.7 +/- 0.4 Pg C a(-1) (inversion) and -1.4 +/- 0.7 Pg C a(-1) (pCO(2)-climatology), respectively, consisting of an outgassing flux of river-derived carbon of similar to+0.5 Pg C a(-1), and an uptake flux of anthropogenic carbon of -2.2 +/- 0.3 Pg C a(-1) (inversion) and -1.9 +/- 0.7 Pg C a(-1) (pCO(2)-climatology). The two flux estimates also imply a consistent description of the contemporary meridional transport of carbon with southward ocean transport throughout most of the Atlantic basin, and strong equatorward convergence in the Indo-Pacific basins. Both transport estimates suggest a small hemispheric asymmetry with a southward transport of between -0.2 and -0.3 Pg C a(-1) across the equator. While the convergence of these two independent estimates is encouraging and suggests that it is now possible to provide relatively tight constraints for the net air-sea CO2 fluxes at the regional basis, both studies are limited by their lack of consideration of long-term changes in the ocean carbon cycle, such as the recent possible stalling in the expected growth of the Southern Ocean carbon sink. [less ▲]

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See detailThe role of ocean transport in the uptake of anthropogenic CO2
Cao, L.; Eby, M.; Ridgwell, A. et al

in Biogeosciences (2009), 6(3), 375-390

We compare modeled oceanic carbon uptake in response to pulse CO2 emissions using a suite of global ocean models and Earth system models. In response to a CO2 pulse emission of 590 Pg C (corresponding to ... [more ▼]

We compare modeled oceanic carbon uptake in response to pulse CO2 emissions using a suite of global ocean models and Earth system models. In response to a CO2 pulse emission of 590 Pg C (corresponding to an instantaneous doubling of atmospheric CO2 from 278 to 556 ppm), the fraction of CO2 emitted that is absorbed by the ocean is: 37 +/- 8\%, 56 +/- 10\%, and 81 +/- 4 (model mean +/- 2 sigma) in year 30, 100, and 1000 after the emission pulse, respectively. Modeled oceanic uptake of pulse CO2 on timescales from decades to about a century is strongly correlated with simulated present-day uptake of chlorofluorocarbons (CFCs) and CO2 across all models, while the amount of pulse CO2 absorbed by the ocean from a century to a millennium is strongly correlated with modeled radiocarbon in the deep Southern and Pacific Ocean. However, restricting the analysis to models that are capable of reproducing observations within uncertainty, the correlation is generally much weaker. The rates of surface-to-deep ocean transport are determined for individual models from the instantaneous doubling CO2 simulations, and they are used to calculate oceanic CO2 uptake in response to pulse CO2 emissions of different sizes pulses of 1000 and 5000 Pg C. These results are compared with simulated oceanic uptake of CO2 by a number of models simulations with the coupling of climate-ocean carbon cycle and without it. This comparison demonstrates that the impact of different ocean transport rates across models on oceanic uptake of anthropogenic CO2 is of similar magnitude as that of climate-carbon cycle feed-backs in a single model, emphasizing the important role of ocean transport in the uptake of anthropogenic CO2. [less ▲]

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See detailCarbon Cycle and Climate Sensitivity in an Earth System Model
Mouchet, Anne ULg; Loutre, M.; Fichefet, T. et al

Poster (2008, December)

The sensitivity of the potential feedbacks between climate and biogeochemical cycles (BGC) is adressed with the help of LOVECLIM, a global three-dimensional Earth system model of intermediate complexity ... [more ▼]

The sensitivity of the potential feedbacks between climate and biogeochemical cycles (BGC) is adressed with the help of LOVECLIM, a global three-dimensional Earth system model of intermediate complexity. Key physical or biogeochemical parameters of LOVECLIM are varied within their range of uncertainty in order to provide an ensemble of parameter sets resulting in contrasted climate and global carbon cycle sensitivities. The selected climate parameter sets lead to a climate sensitivity ranging from 2 to 4°C and a reduction of the Atlantic meridional overturning circulation (MOC) ranging from 20 to 60% after 1 kyr in response to identical external forcings. The key parameters for the carbon cycle were chosen among those with the largest impact on the marine biogeochemical cycle and on the response of atmospheric CO2 to emission scenario. We then analyze the results of freshwater hosing experiments in which both the climate parameters and the BGC parameters are modified. These experiments allow to examine the impact of changes in climate sensitivity and of MOC reduction over the biogeochemical cycles as well as to assess the potential feedback from the carbon cycle onto the climate. A decreasing MOC directly impacts the ocean biogeochemistry. Most of the model setups show a decline in export production although some parameter sets yield reorganisation of the large scale ocean circulation, which leads to different behaviour of the ocean biogeochemistry. The atmospheric carbon is also affected by a decrease of the MOC. While most parameter sets cause a modest increase in atmospheric CO2, consecutive to the decrease of the continental vegetation, some model versions exhibit an amplification of the atmospheric CO2 response to the forcing. The mechanisms leading to the different responses for the different parameter sets are examined and discussed. [less ▲]

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See detailOcean biogeochemical cycles and climate sensitivity in an Earth system model
Mouchet, Anne ULg; Loutre, M. F.; Fichefet, T. et al

Conference (2008, October)

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See detailOxygen, a tool for assessing ocean tracer transport models
Mouchet, Anne ULg

Poster (2008, April)

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See detailOcean biogeochemical cycles and climate sensitivity in an Earth system model
Mouchet, Anne ULg; Loutre, M. F.; Fichefet, T. et al

Conference (2008, April)

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See detailLong-term climate commitments projected with climate-carbon cycle models
Plattner, G. K.; Knutti, R.; Joos, F. et al

in Journal of Climate (2008), 21(12), 2721-2751

Eight earth system models of intermediate complexity (EMICs) are used to project climate change commitments for the recent Intergovernmental Panel on Climate Change's (IPCC's) Fourth Assessment Report ... [more ▼]

Eight earth system models of intermediate complexity (EMICs) are used to project climate change commitments for the recent Intergovernmental Panel on Climate Change's (IPCC's) Fourth Assessment Report (AR4). Simulations are run until the year 3000 A. D. and extend substantially farther into the future than conceptually similar simulations with atmosphere-ocean general circulation models (AOGCMs) coupled to carbon cycle models. In this paper the following are investigated: 1) the climate change commitment in response to stabilized greenhouse gases and stabilized total radiative forcing, 2) the climate change commitment in response to earlier CO2 emissions, and 3) emission trajectories for profiles leading to the stabilization of atmospheric CO2 and their uncertainties due to carbon cycle processes. Results over the twenty-first century compare reasonably well with results from AOGCMs, and the suite of EMICs proves well suited to complement more complex models. Substantial climate change commitments for sea level rise and global mean surface temperature increase after a stabilization of atmospheric greenhouse gases and radiative forcing in the year 2100 are identified. The additional warming by the year 3000 is 0.6-1.6 K for the low-CO2 IPCC Special Report on Emissions Scenarios (SRES) B1 scenario and 1.3-2.2 K for the high-CO2 SRES A2 scenario. Correspondingly, the post-2100 thermal expansion commitment is 0.3-1.1 m for SRES B1 and 0.5-2.2 m for SRES A2. Sea level continues to rise due to thermal expansion for several centuries after CO2 stabilization. In contrast, surface temperature changes slow down after a century. The meridional overturning circulation is weakened in all EMICs, but recovers to nearly initial values in all but one of the models after centuries for the scenarios considered. Emissions during the twenty-first century continue to impact atmospheric CO2 and climate even at year 3000. All models find that most of the anthropogenic carbon emissions are eventually taken up by the ocean (49%-62%) in year 3000, and that a substantial fraction (15%-28%) is still airborne even 900 yr after carbon emissions have ceased. Future stabilization of atmospheric CO2 and climate change requires a substantial reduction of CO2 emissions below present levels in all EMICs. This reduction needs to be substantially larger if carbon cycle-climate feedbacks are accounted for or if terrestrial CO2 fertilization is not operating. Large differences among EMICs are identified in both the response to increasing atmospheric CO2 and the response to climate change. This highlights the need for improved representations of carbon cycle processes in these models apart from the sensitivity to climate change. Sensitivity simulations with one single EMIC indicate that both carbon cycle and climate sensitivity related uncertainties on projected allowable emissions are substantial. [less ▲]

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See detailClimate and marine carbon cycle response to changes in the strength of the Southern Hemispheric westerlies
Menviel, L.; Timmermann, A.; Mouchet, Anne ULg et al

in Paleoceanography (2008), 23(4),

It has been previously suggested that changes in the strength and position of the Southern Hemisphere westerlies could be a key contributor to glacial-interglacial atmospheric CO2 variations. To test this ... [more ▼]

It has been previously suggested that changes in the strength and position of the Southern Hemisphere westerlies could be a key contributor to glacial-interglacial atmospheric CO2 variations. To test this hypothesis, we perform a series of sensitivity experiments using an Earth system model of intermediate complexity. A strengthening of the climatological mean surface winds over the Southern Ocean induces stronger upwelling and increases the formation of Antarctic Bottom Water. Enhanced Ekman pumping brings more dissolved inorganic carbon (DIC)-rich waters to the surface. However, the stronger upwelling also supplies more nutrients to the surface, thereby enhancing marine export production in the Southern Hemisphere and decreasing the DIC content in the euphotic zone. The net response is a small atmospheric CO2 increase (similar to 5 ppmv) compared to the full glacial-interglacial CO2 amplitude of similar to 90 ppmv. Roughly the opposite results are obtained for a weakening of the Southern Hemisphere westerly winds. [less ▲]

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See detailMeridional reorganizations of marine and terrestrial productivity during Heinrich events,
Menviel, L.; Timmermann, A.; Mouchet, Anne ULg et al

in Paleoceanography (2008), 23

To study the response of the global carbon cycle to a weakening of the Atlantic Meridional Overturning Circulation (AMOC), a series of freshwater perturbation experiments is conducted both under ... [more ▼]

To study the response of the global carbon cycle to a weakening of the Atlantic Meridional Overturning Circulation (AMOC), a series of freshwater perturbation experiments is conducted both under preindustrial and glacial conditions using the earth system model of intermediate complexity LOVECLIM. A shutdown of the AMOC leads to substantial cooling of the North Atlantic, a weak warming of the Southern Hemisphere, intensification of the northeasterly trade winds, and a southward shift of the Intertropical Convergence Zone (ITCZ). Trade wind anomalies change upwelling in the tropical oceans and hence marine productivity. Furthermore, hydrological changes associated with a southward displacement of the ITCZ lead to a reduction of terrestrial carbon stocks mainly in northern Africa and northern South America in agreement with paleoproxy data. In the freshwater perturbation experiments the ocean acts as a sink of CO2, primarily through increased solubility. The net atmospheric CO2 anomaly induced by a shutdown of the AMOC amounts to about +15 ppmv and −10 ppmv for preindustrial and glacial conditions, respectively. This background state dependence can be explained by the fact that the glacial climate is drier and the terrestrial vegetation therefore releases a smaller amount of carbon to the atmosphere. This study demonstrates that the net CO2 response to large-scale ocean circulation changes has significant contributions both from the terrestrial and marine carbon cycle. [less ▲]

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See detailThe leaky funnel model, a metaphor of the ventilation of the World Ocean as simulated in an OGCM
Mouchet, Anne ULg; Deleersnijder, Eric

in Tellus : Series A (2008), 60(4), 761-774

It is seen that an idealized model may suggest an appropriate scaling of the water age in the World Ocean, which is a measure of the ventilation rate. We use a 1-D advection-diffusion model in which the ... [more ▼]

It is seen that an idealized model may suggest an appropriate scaling of the water age in the World Ocean, which is a measure of the ventilation rate. We use a 1-D advection-diffusion model in which the deep ocean is represented as a leaky funnel, allowing recirculation towards the surface. The analytical solutions to the steady-state problem are readily obtained. The three parameters of the leaky funnel model are estimated in such a way that the behaviour of the domain-averaged water age be as similar as possible to that derived from a 3-D model in a series of sensitivity runs. The agreement between both sets of mean ages is excellent, with a linear correlation coefficient very close to unity. A good agreement is also found for the age of radioactive tracers and the associated radioages. The parameters of the leaky funnel model have a clear physical meaning, that is, the order of magnitude of the horizontal velocity, the mean length of water parcel trajectories in the deep ocean, and a horizontal diffusivity scale. The values of all of them turn out to be consistent with our current knowledge of the World Ocean circulation. [less ▲]

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See detailModeling the influence of the Greenland ice sheet melting on the Atlantic meridional overturning circulation during the next millennia
Fichefet, Thierry; Driesschaert, Emmanuelle; Goosse, Hugues et al

Conference (2007, April 19)

A three-dimensional Earth system model of intermediate complexity including a dynamic ice sheet component has been used to investigate the long-term evolution of the Greenland ice sheet and its effects on ... [more ▼]

A three-dimensional Earth system model of intermediate complexity including a dynamic ice sheet component has been used to investigate the long-term evolution of the Greenland ice sheet and its effects on the Atlantic meridional overturning circulation (AMOC) in response to a range of stabilized anthropogenic forcings. Our results suggest that the Greenland ice sheet volume should experience a significant decrease in the future. For a radiative forcing exceeding 7.5 W m-2, the modeled ice sheet melts away within 3000 years. A number of feedbacks operate during this deglaciation, implying a strong non-linear relationship between the radiative forcing and the melting rate. In the most extreme scenario considered, the freshwater flux from Greenland into the surrounding oceans is higher than 0.1 Sv during a few centuries. This is however insufficient to induce a shutdown of the AMOC in the model. [less ▲]

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