Publications of Guy Munhoven
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See detailEffects of CO2, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study
Henrot, Alexandra ULiege; François, Louis ULiege; Favre, Eric ULiege et al

in Climate of the Past (2010), 6

The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support ... [more ▼]

The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support warmer and more humid climate during the MMCO. The mechanisms responsible for the warmer climate at the MMCO and particularly the role of the atmospheric carbon dioxide are still highly debated. Here we carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the absence of ice on the continents, the opening of the Central American and Eastern Tethys Seaways, the lowering of the topography on land, the effect of various atmospheric CO2 concentrations and the vegetation feedback. Our results show that a higher than present-day CO2 concentration is necessary to generate a warmer climate at all latitudes at the Middle Miocene, in agreement with the terrestrial proxy reconstructions which suggest high atmospheric CO2 concentrations at the MMCO. Nevertheless, the changes in sea-surface conditions, the lowering of the topography on land and the vegetation feedback also produce significant local warming that may, locally, even be stronger than the CO2 induced temperature increases. The lowering of the topography leads to a more zonal atmospheric circulation and allows the westerly flow to continue over the lowered Plateaus at mid-latitudes. The reduced height of the Tibetan Plateau notably prevents the development of a monsoon-like circulation, whereas the reduction of elevations of the North American and European reliefs strongly increases precipitation from northwestern to eastern Europe. The changes in vegetation cover contribute to maintain and even to intensify the warm and humid conditions produced by the other factors, suggesting that the vegetation-climate interactions could help to improve the model-data comparison. [less ▲]

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See detailHolocene carbon cycle dynamics
Kleinen, Thomas; Brovkin, Victor; von Bloh, Werner et al

in Geophysical Research Letters (2010), 37

We are investigating the late Holocene rise in CO2 by performing four experiments with the climate-carbon-cycle model CLIMBER2-LPJ. Apart from the deep sea sediments, important carbon cycle processes ... [more ▼]

We are investigating the late Holocene rise in CO2 by performing four experiments with the climate-carbon-cycle model CLIMBER2-LPJ. Apart from the deep sea sediments, important carbon cycle processes considered are carbon uptake or release by the vegetation, carbon uptake by peatlands, and CO2 release due to shallow water sedimentation of CaCO3. Ice core data of atmospheric CO2 between 8 ka BP and preindustrial climate can only be reproduced if CO2 outgassing due to shallow water sedimentation of CaCO3 is considered. In this case the model displays an increase of nearly 20 ppmv CO2 between 8 ka BP and present day. Model configurations that do not contain this forcing show a slight decrease in atmospheric CO2. We can therefore explain the late Holocene rise in CO2 by invoking natural forcing factors only, and anthropogenic forcing is not required to understand preindustrial CO2 dynamics. [less ▲]

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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 detailFuture CCD and CSH variations: Deep-sea impact of ocean acidification
Munhoven, Guy ULiege

Poster (2009, June)

The evolutions of atmospheric CO2 partial pressure (pCO2) and of the carbonate compensation depth and the calcite and aragonite saturation horizons (CSH and ASH, respectively) have been studied with the ... [more ▼]

The evolutions of atmospheric CO2 partial pressure (pCO2) and of the carbonate compensation depth and the calcite and aragonite saturation horizons (CSH and ASH, respectively) have been studied with the coupled oceansediment model MBM-MEDUSA [1], over the next 50,000 years. MBM-MEDUSA includes a full description of sedimentary exchange processes, taking into account chemical carbonate erosion in a consistent way. The adopted emission scenarios were based upon logistic functions [2], considering total emissions of 500, 1000, 2000 and 4240 GtC); the adopted stabilisation scenarios were the S350, S450, S550, S650 and S750 from the IPCC [3]. While the evolutions of atmospheric pCO2 and pH have got a great deal of attention so far (e.g., [4, 5]), only a few studies have considered the saturation horizons [5, 6], and, to our best knowledge, this is the first study also focusing on compensation depth variations. Simulation experiments were started with a 50,000 year spin-up to 1750 A.D. (at steady state). This state was characterised by an atmospheric pCO2 of 277 ppm, a CSH depth of 3350 m and a CCD of 4300 m (in the Indo-Pacific, which can be considered the most representative reservoir for the global ocean). In all experiments, we found that CCD variations were considerably greater than CSH variations. The 500 GtC emission scenario yielded CSH and CCD maximum shoalings of 450 and 800 m, respectively, in the year 3400 A.D. about; with the 4240 GtC emission scenario, both CSH and CCD became shallower than 500 m in 2650 A.D. With the highly optimistic S350 stabilisation scenario, CSH and CCD become even shallower than with the 500 GtC emission scenario (650 m and 1000 m shoaling, respectively), although in the year 5000 A.D. only. For the close-to-CO2-doubling scenario S550, CSH and CCD shoaled by about 1950 and 2450 m (to depths of 1400 and 1900 m, respectively). As a result, most of the sea-floor environment bathed in water that was highly corrosive to carbonate material. In the S650 and S750 scenarios experiments, the CCD becomes shallower than 500 m, leaving little space for benthic carbonate producers to survive. [1] Munhoven (2007) Deep-Sea Res. II 54, 722-746. [2] Bacastow and Dewey (1996) Energy Convers. Mgmt. 37, 1079-1086. [3] IPCC (1994) Climate Change 1994, Cambridge University Press. [4] Caldeira and Wickett (2003) Nature 425, 325-325. [5] Orr et al. (2005) Nature 437, 681-686. [6] Cao and Caldeira (2008) Geophys. Res. Lett. 35, L19609. [less ▲]

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See detailImpacts of Climate Change on Tropical and Subtropical Ecosystems
François, Louis ULiege; Favre, E.; Henrot, Alexandra-Jane ULiege et al

Conference (2009, June)

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See detailMiddle Miocene climate and vegetation modelling with PLASIM and CARAIB
Henrot, Alexandra ULiege; François, Louis ULiege; Favre, Eric ULiege et al

Conference (2009, April 21)

In a long-term climatic cooling trend, the Middle Miocene represents one of the last warm periods of the Neogene, culminating with the Miocene Climatic Optimum, MCO (17-15 My). Palynological studies ... [more ▼]

In a long-term climatic cooling trend, the Middle Miocene represents one of the last warm periods of the Neogene, culminating with the Miocene Climatic Optimum, MCO (17-15 My). Palynological studies suggest that the warmer climatic conditions prevailing during the MCO allowed warm forests to expand poleward of the subtropical zone, with evergreen forests proliferating in North America and Europe (Jimenez-Moreno and Suc, 2007, Palaeogeogr. Palaeoclimatol. Palaeoecol. 253: 208-225). In this work, we used the Planet Simulator (Fraedrich et al., 2005, Meteorol. Z. 14: 299-304 and 305-314), an Earth system model of intermediate complexity, to carry out several simulation experiments, where we have assessed the effects of the absence of ice on the continents, the opening of the Central American and Eastern Tethys seaways, the lowering of the topography on land and the effect of various atmospheric CO2 concentrations, in agreement with the values reported in the litterature. We then produced several vegetation distributions, using the dynamic vegetation model CARAIB (Galy et al., 2008, Quat. Sci. Rev. 27: 1396-1409), to analyse if the climatic forcings considered are sufficient to explain the expansion of warmer forest types to higher latitudes. Our results indicate that an increase of atmospheric CO2 concentration, higher than the present-day one, is necessary to allow subtropical forest types to expand poleward. This result agrees with recent paleo-atmospheric CO2 reconstruction from stomatal frequency analysis, which suggests 500 ppmv of CO2 during the MCO. However, the required warming may be due to processes not considered in our setup (e.g. full oceanic circulation or other greenhouse gases). [less ▲]

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See detailImpacts of land surface properties and atmospheric CO2 on the Last Glacial Maximum climate: a factor separation analysis
Henrot, Alexandra ULiege; François, Louis ULiege; Brewer, S. et al

in Climate of the Past (2009), 5(2), 183-202

Many sensitivity studies have been carried out, using climate models of different degrees of complexity to test the climate response to Last Glacial Maximum boundary conditions. Here, instead of adding ... [more ▼]

Many sensitivity studies have been carried out, using climate models of different degrees of complexity to test the climate response to Last Glacial Maximum boundary conditions. Here, instead of adding the forcings successively as in most previous studies, we applied the separation method of U. Stein et P. Alpert 1993, in order to determine rigorously the different contributions of the boundary condition modifications, and isolate the pure contributions from the interactions among the forcings. We carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the ice sheet expansion and elevation, the lowering of the atmospheric CO2 and of the vegetation cover change on the LGM climate. The separation of the ice cover and orographic contributions shows that the ice albedo effect is the main contributor to the cooling of the Northern Hemisphere, whereas orography has only a local cooling impact over the ice sheets. The expansion of ice cover in the Northern Hemisphere causes a disruption of the tropical precipitation, and a southward shift of the ITCZ. The orographic forcing mainly contributes to the disruption of the atmospheric circulation in the Northern Hemisphere, leading to a redistribution of the precipitation, but weakly impacts the tropics. The isolated vegetation contribution also induces strong cooling over the continents of the Northern Hemisphere that further affects the tropical precipitation and reinforce the southward shift of the ITCZ, when combined with the ice forcing. The combinations of the forcings generate many non-linear interactions that reinforce or weaken the pure contributions, depending on the climatic mechanism involved, but they are generally weaker than the pure contributions. Finally, the comparison between the LGM simulated climate and climatic reconstructions over Eurasia suggests that our results reproduce well the south-west to north-east temperature gradients over Eurasia. [less ▲]

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See detailAtmospheric Lifetime of Fossil Fuel Carbon Dioxide
Archer, David; Eby, Michael; Brovkin, Victor et al

in Annual Review of Earth and Planetary Sciences (2009), 37

CO2 released from combustion of fossil fuels equilibrates among the various carbon reservoirs of the atmosphere, the ocean, and the terrestrial biosphere on timescales of a few centuries. However, a ... [more ▼]

CO2 released from combustion of fossil fuels equilibrates among the various carbon reservoirs of the atmosphere, the ocean, and the terrestrial biosphere on timescales of a few centuries. However, a sizeable fraction of the CO2 remains in the atmosphere, awaiting a return to the solid earth by much slower weathering processes and deposition of CaCO3. Common measures of the atmospheric lifetime of CO2, including the e-folding time scale, disregard the long tail. Its neglect in the calculation of global warming potentials leads many to underestimate the longevity of anthropogenic global warming. Here, we review the past literature on the atmospheric lifetime of fossil fuel CO2 and its impact on climate, and we present initial results from a model intercomparison project on this topic. The models agree that 20–35% of the CO2 remains in the atmosphere after equilibration with the ocean (2–20 centuries). Neutralization by CaCO3 draws the airborne fraction down further on timescales of 3 to 7 kyr. [less ▲]

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See detailInteractive comment on “Presentation, calibration and validation of the low-order, DCESS Earth System Model” by G. Shaffer et al.
Munhoven, Guy ULiege

in Geoscientific Model Development Discussions (2008), 1

The paper "Presentation, calibration and validation of the low-order, DCESS Earth System Model” by G. Shaffer et al. is reviewed.

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See detailGlacial-interglacial pCO2 Variations and the Rain Ratio Hypothesis: Implications for Sedimentary Carbonate Preservation/Dissolution Processes
Munhoven, Guy ULiege

Conference (2008, May 27)

A reduction of the carbonate-carbon to organic-carbon export rain ratio during glacial times has been for years one of the favourite hypotheses to explain the glacial-interglacial atmospheric CO2 ... [more ▼]

A reduction of the carbonate-carbon to organic-carbon export rain ratio during glacial times has been for years one of the favourite hypotheses to explain the glacial-interglacial atmospheric CO2 variations. This hypothesis have been tested and implications for the dynamics of sedimentary carbonate preservation and dissolution explored with MBM, a multi-box model of the ocean carbon cycle, fully coupled to the transient early diagenesis model MEDUSA. With this coupled model, a peak reduction of the rain ratio by 40% at the Last Glacial Maximum (LGM) was found to produce a net atmospheric pCO2 reduction of about 40 ppm. Changing shelf carbonate accumulation rates and continental weathering inputs produced a 55-60 ppm reduction. The combination of the two mechanisms generates a 90-95 ppm pCO2 change, which compares well with the observations. However, the resulting model sedimentary record is at odds with actual sedimentary records. Changing carbonate accumulation rates on the continental shelf and variable weathering fluxes depress the calcite saturation horizon (CSH) by about 1 km at the LGM; rain ratio variations depress it by another km. In addition to this large amplitude for the CSH, the changing rain ratio also leads to transition zone changes in the model sedimentary record that are opposite in phase with data-based reconstructions. [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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See detailImpacts of vegetation changes on LGM climate
Henrot, Alexandra ULiege; François, Louis ULiege; Munhoven, Guy ULiege

Conference (2007, March 12)

The impacts of vegetation change on the climate at the Last Glacial Maximum are investigated with the Earth System Model of Intermediate Complexity Planet Simulator and the dynamic vegetation model Caraib ... [more ▼]

The impacts of vegetation change on the climate at the Last Glacial Maximum are investigated with the Earth System Model of Intermediate Complexity Planet Simulator and the dynamic vegetation model Caraib (CARbon Assimilation in the Biosphere). [less ▲]

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See detailInteractive comment on “Application of sediment core modelling to understanding climates of the past: An example from glacial-interglacial changes in Southern Oceansilica cycling” by A. Ridgwell
Munhoven, Guy ULiege

in Climate of the Past Discussions (2007), 2

The paper “Application of sediment core modelling to understanding climates of the past: An example from glacial-interglacial changes in Southern Oceansilica cycling” by A. Ridgwell is reviewed and ... [more ▼]

The paper “Application of sediment core modelling to understanding climates of the past: An example from glacial-interglacial changes in Southern Oceansilica cycling” by A. Ridgwell is reviewed and comented. [less ▲]

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See detailGlacial–interglacial rain ratio changes: Implications for atmospheric CO2 and ocean–sediment interaction
Munhoven, Guy ULiege

in Deep-Sea Research. Part II, Topical Studies in Oceanography (2007), 54(5-7), 722-746

A reduction of the carbonate-carbon to organic-carbon export rain ratio during glacial times has been advanced to explain the glacial–interglacial atmospheric CO2 variations. This hypothesis is tested and ... [more ▼]

A reduction of the carbonate-carbon to organic-carbon export rain ratio during glacial times has been advanced to explain the glacial–interglacial atmospheric CO2 variations. This hypothesis is tested and implications for the dynamics of sedimentary carbonate preservation and dissolution are explored with a multi-box model (MBM) of the ocean carbon cycle, fully coupled to a new transient early diagenesis model (called MEDUSA). A peak reduction of the rain ratio by 40% at the Last Glacial Maximum (LGM) was found to produce a net atmospheric pCO2 reduction of about 40 ppm. Changing shelf carbonate accumulation rates and continental weathering inputs produced a 55–60 ppm reduction. The combination of the two mechanisms generates a pCO2 change of 90–95 ppm, which compares well with the observed data. However, the resulting model sedimentary record does not conform to actual sedimentary records. The changes related to continental shelf processes and variable weathering flux depress the calcite saturation horizon (CSH) by about 1 km at the LGM; if rain ratio variations are also considered, that depression increases by another km. In addition to this large amplitude for the CSH, possibly due to the adopted box-model approach, the changing rain ratio also leads to transition zone changes in the model sedimentary record that are opposite in phase with data-based reconstructions. Realistic changes in the aragonite fraction of the carbonate rain were found to have only a minimal impact on atmospheric pCO2. Finally, chemical erosion of deep-sea sediment was shown to reduce the amplitude of variation of the sedimentary CCD by about 10–20%. It may provide a mechanism to improve the model-data agreement. [less ▲]

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