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See detailEuropean bioclimatic affinity groups: Data-model comparisons
Laurent, Jeanne-Marine; François, Louis ULg; Bar-Hen, Avner et al

in Global and Planetary Change (2008), 61(1-2), 28-40

Global vegetation models are remarkably effective when considering large areas such as Europe. However, their accuracy at finer scales remains to be tested. In this paper, we validate the simulation of ... [more ▼]

Global vegetation models are remarkably effective when considering large areas such as Europe. However, their accuracy at finer scales remains to be tested. In this paper, we validate the simulation of modem potential vegetation by the CARbon Assimilation In the Biosphere (CARAIB) model in Europe. Then, in order to evaluate the simulation of tree group distributions at a finer scale, in France, we present a comparison between observed distributions, distributions reconstructed from palynological data, and model simulated ranges. The results will help to validate past vegetation simulations. For this analysis, we use Bioclimatic Affinity Groups (BAGs), based on vegetation groups' climatic tolerances and requirements. The CARAIB model was adapted to simulate the net primary productivity (NPP), biomass and range of the arboreal BAGs. In Europe, at a 30' latitude/longitude grid scale, simulated NPP of BAGs are used to define classes of vegetation as being present or absent, with a classification rule, based on Kappa statistics. In France, at a 10' lat./long. scale, a second discriminant analysis, based on Classification And Regression Tree (CART), allows for a similar classification with BAG pollen percentages. At each palynological sampling site, we then compared the simulation to the reconstruction from pollen data. With 30' lat./long. resolution, most thresholds that discriminate NPP into absence or presence classes are low, ranging from 1 to 77 g/m(2). Agreement indices between observed and simulated distributions range from 0.4 to 0.83, with broad scale BAG potential patterns and boundaries being accurately simulated by CARAIB. In France, on the 10' lat./long. scale, pollen percentages correctly account for BAG presence/absence despite non-linear pollen-vegetation relationships. Agreement ratios between observed and reconstructed patterns range from 0.53 to 0.95. At the 10' lat./long. scale, the validation of simulated ranges with pollen data is reliable for 9 of 13 arboreal BAGs and acceptable for three more BAGs. The discrepancies highlight the gap between potential and actual distribution areas. The filling of simulated potential ranges, such as the Atlantic coast and near Mediterranean border, are uncompleted as actual ranges are limited by a number of climate and dispersal constraints related to competition as well as historical, geographical and anthropogenic factors. Our results suggest that the simulation of these constraints would be a major improvement for the CARAIB model. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailCarbon cycle and hydrology in the palaeo-terrestrial environments
François, Louis ULg; Probst, Jean-Luc

in Global and Planetary Change (2008), 61(1-2), 1-2

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See detailHigh-resolution diatom/clay record in Lake Baikal from grey scale, and magnetic susceptibility over Holocene and Termination I
Boes, Xavier; Piotrowska, Natalia; Fagel, Nathalie ULg

in Global and Planetary Change (2005), 46(1-4), 299-313

Tracing past climate signals from Lake Baikal sediments with a "multi-annual' resolution by conventional techniques is a difficult challenge since the sedimentation rates from Termination I up to the ... [more ▼]

Tracing past climate signals from Lake Baikal sediments with a "multi-annual' resolution by conventional techniques is a difficult challenge since the sedimentation rates from Termination I up to the present range from 0.004 to 0.17 mm/year. In this paper, climate signals are reconstructed from three continuous sediment records from Vydrino Shoulder and Posolsky Bank in the Southern Basin, and Continent Ridge in the Northern Basin. For each coring site, a calendar age model was constructed using calibrated radiocarbon ages. The magnetic susceptibility is used to better constrain the age models over OIS4 to OIS1 The cores have been hardened using polymerized technique in order to allow the easy cut of thin sections that contain evidence for narrow biogenic/clayey laminations. The grey scale taken from the thin sections is used here as a high-resolution proxy record of diatom/clay ratio. The grey density values are qualitatively interpreted against the sediment components by optical microscopy from the thin sections. In the Northern Basin, the Continent station provides the best age model and sediment resolution over the Termination I period. In particular, four optima (i.e. Bolling, Allerod, Atlantic, and Subboreal) are indicated by substantial increases of the grey scale, whereas cold periods like the Younger Dryas correspond to lower grey scale values. We emphasize that the short-term variations in the grey scale at 20 mu m resolution could correspond to short climate responses in Lake Baikal sediments. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailA qualitative assessment of the influence of bioturbation in Lake Baikal sediments
Martin, Patrick; Boes, Xavier; Goddeeris, Baudouin et al

in Global and Planetary Change (2005), 46(1-4), 87-99

The impact of bioturbation in Lake Baikal sediments, particularly on rhythmic layering and mixing, was assessed by studying the actual vertical distribution of benthic animals in continuous accumulation ... [more ▼]

The impact of bioturbation in Lake Baikal sediments, particularly on rhythmic layering and mixing, was assessed by studying the actual vertical distribution of benthic animals in continuous accumulation zones selected by seismic survey (Vydrino, Shoulder, Posolskoe Bank, Continent Ridge). To assess the influence of the bioturbation, animals were extracted from short cores and identified at the relevant taxonomic level. The faunal distribution is examined in parallel with the bioturbation tracks observed in thin section. Oligochaeta, Nematoda, Ostracoda, Copepoda, Gammaridae, Chironomidae and Hydrachnidia were found inhabiting the sediment. Among them, only oligochaete worms were assumed to have a significant impact on sediment mixing because of their "conveyor belt" feeding. The other two most abundantly sampled groups, nematods and copepods, belong to the interstitial fauna that has no significant impact on the vertical displacement of sediment particles and do not ingest the sediment. The presence of a benthic fauna as deep as 15 cm in the sediment indicates that the possibility of sediment disturbance by invertebrate activity cannot be dismissed in Lake Baikal. The effect of biological mixing is more limited in the deepest stations because the number of potential bioturbators is reduced, qualitatively as well as quantitatively. Located in the abyssal zone, Continent and Vydrino (but outside turbidites) deep stations appear to be most promising sediment records for tracking climate signal at high resolution. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailVivianite formation and distribution in Lake Baikal sediments
Fagel, Nathalie ULg; Alleman, L. Y.; Granina, L. et al

in Global and Planetary Change (2005), 46(1-4), 315-336

In an effort to better understand vivianite formation processes, four Lake Baikal sediment cores spanning two to four interglacial stages in the northern, central and southern basins and under various ... [more ▼]

In an effort to better understand vivianite formation processes, four Lake Baikal sediment cores spanning two to four interglacial stages in the northern, central and southern basins and under various biogeochemical environments are scrutinized. The vivianite-rich layers were detected by anomalous P-enrichments in bulk geochemistry and visually by observations on X-radiographs. The millimetric concretions of vivianite were isolated by sieving and analysed by X-ray diffraction, scanning electron microscope (SEM), microprobe, infrared spectroscopy, inductively coupled plasma atomic emission spectrometry and mass spectrometry (ICP-AES, ICP-MS). All the vivianites display similar morphological, mineralogical and geochemical signature, suggesting a common diagenetic origin. Their geochemical signature is sensitive to secondary alteration where vivianite concretions are gradually transformed from the rim to the center into an amorphous santabarbaraite phase with a decreasing Mn content. We analysed the spatial and temporal distribution of the concretions in order to determine the primary parameters controlling the vivianite formation, e.g., lithology, sedimentation rates, and porewater chemistry. We conclude that vivianite formation in Lake Baikal is mainly controlled by porewater chemistry and sedimentation rates, and it is not a proxy for lacustrine paleoproductivity. Vivianite accumulation is not restricted to areas of slow sedimentation rates (e.g., Academician and Continent ridges). At the site of relatively fast sedimentation rate, i.e., the Posolsky Bank near the Selenga Delta, vivianite production may be more or less related to the Selenga River inputs. It could be also indirectly related to the past intensive methane escapes from the sediments. While reflecting an early diagenetic signal, the source of P and Fe porewater for vivianites genesis is still unclear. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailSedimentary dynamics on isolated highs in Lake Baikal: evidence from detailed high-resolution geophysical data and sediment cores
Charlet, F.; Fagel, Nathalie ULg; De Batist, M. et al

in Global and Planetary Change (2005), 46(1-4), 125-144

High- and very-high-resolution seismic data, side-scan sonar mosaics and piston cores from three isolated highs in Lake Baikal (Vydrino Shoulder, Posolsky Bank, Continent Ridge) have allowed to document ... [more ▼]

High- and very-high-resolution seismic data, side-scan sonar mosaics and piston cores from three isolated highs in Lake Baikal (Vydrino Shoulder, Posolsky Bank, Continent Ridge) have allowed to document in unprecedented detail the depositional, re-depositional and tectonic processes and to characterise the overall sedimentary environment on such isolated highs. Our data show that Vydrino Shoulder actually represents a turbidity- or underflow-sourced slope fan, with a distinct channel-levee morphology, and affected by tectonics and stratigraphic unconformities. Sediment cores contain up to 90% of terrigenous material. Posolsky Bank is a major tilted fault block, clearly affected by tectonic activity, by stratigraphic unconformities and by mass wasting along its margins. Sedimentation on its crest is undisturbed, but average sedimentation rates are high due to the influence of the nearby Selenga River. Continent Ridge is also affected by active faulting, stratigraphic unconformities and by mass-wasting along its flanks. The area receives only 30% of terrigenous input. There are no signs of sediment reworking due to bottom-currents. Our study thus shows that in comparison with other environments in Lake Baikal, the isolated highs probably hold the best potential to contain a high-quality, continuous, undisturbed and undiluted sedimentary record suitable for paleoclimate research. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailBiospheric carbon stocks reconstructed at the Last Glacial Maximum: comparison between general circulation models using prescribed and computed sea surface temperatures
Otto, D.; Rasse, Daniel; Kaplan, J. et al

in Global and Planetary Change (2002), 33(1-2), 117-138

The terrestrial biosphere model Carbon Assimilation in the Biosphere (CARAIB) was improved by introducing two vegetation storeys and implementing a new module which simulates the equilibrium distribution ... [more ▼]

The terrestrial biosphere model Carbon Assimilation in the Biosphere (CARAIB) was improved by introducing two vegetation storeys and implementing a new module which simulates the equilibrium distribution of the vegetation inferred from physiological processes and climatic constraints. In this fourth version of CARAIB, we differentiate ground-level grasses from tree canopies, which allows us to determine the light available to grasses as a direct function of the leaf area index (LAI) of the forest canopy. Both of these storeys are potentially composed of several plant functional types (PFT). The cover fraction of each PFT within each storey is estimated according to its respective net primary productivity (NPP). A biome is assigned to each grid cell on the basis of three physiological criteria: (1) the cover fraction, (2) the NPP, and (3) the LAI; and two climatic constraints: (1) the growing degree-days (GDD) and (2) the lowest temperature reached during the cold season (T-min), which are well-known indices of vegetation expansion boundaries. Total biospheric carbon stocks (vegetation + soil) are reconstructed by forcing the model with eight climatic scenarios of the Last Glacial Maximum (LGM, 21 ka BP), which were obtained from the Palco-Modelling Intercomparison Project (PMIP) from four general circulation models (MRI2, UGAMP, LMD4, and GEN2) using prescribed and computed sea surface temperatures (SSTs). The model was also forced with a current climate together with a preindustrial atmospheric CO2 level of 280 ppm as reference simulation, To validate the model, current biome distribution is reconstructed and compared, for the modem climate, with two distributions of potential vegetation and, for the LGM, with pollen data. The model simulations are in good agreement with broad-scale patterns of vegetation distribution, The results indicate an increase in the total biospheric carbon stock of 827.8-1106.1 Gt C since the LGM. Sensitivity analyses were performed to discriminate the relative effects of the atmospheric CO, level ("fertilization effect"), the climate (present or LGM), and the sea level. Our results suggest that the CO, fertilization effect is mostly responsible for the total increase in vegetation and soil carbon stocks. The four GCMs diverged in their predicted responses of continental climate to calculated SSTs. Only one of them, i.e., MRI2, predicted a marked decline of the continental temperatures in response to lower calculated SSTs. For this GCM, the effect of reduced SSTs on continental biospheric carbon stocks was a decrease of 544.1 Gt for the soil carbon stock and of 283.7. [less ▲]

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See detailThe global carbon cycle and its changes over glacial-interglacial cycles - Preface
François, Louis ULg; Faure, H.; Probst, J. L.

in Global and Planetary Change (2002), 33(1-2), -

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See detailModelled glacial and non-glacial HCO3-, Si and Ge fluxes since the LGM: little potential for impact on atmospheric CO2 concentrations and a potential proxy of continental chemical erosion, the marine Ge/Si ratio
Jones, Ian W; Munhoven, Guy ULg; Tranter, Martyn et al

in Global and Planetary Change (2002), 33(1-2), 139-153

The runoff and riverine fluxes of HCO3-, Si and Ge that arise from chemical erosion in non-glaciated terrain, are modelled at six time steps from the Last Glacial Maximum (LGM) to the present day. The ... [more ▼]

The runoff and riverine fluxes of HCO3-, Si and Ge that arise from chemical erosion in non-glaciated terrain, are modelled at six time steps from the Last Glacial Maximum (LGM) to the present day. The fluxes that arise from the Great Ice Sheets are also modelled. Terrestrial HCO3- fluxes decrease during deglaciation, largely because of the reduction in the area of the continental shelves as sea level rises. The HCO3- fluxes. and the inferred consumption of atmospheric CO2 are used as inputs to a carbon cycle model that estimates their impact on atmospheric CO2 concentrations ((CO2)-C-atms). A maximum perturbation of (CO2)-C-atms by similar to 5.5 ppm is calculated, The impact of solutes from glaciated terrain is small in comparison to those from non-glaciated terrain. Little variation in terrestrial Si and Ge fluxes is calculated (< 10%). However, the global average riverine Ge/Si ratio may be significantly perturbed if the glacial Ge/Si ratio is high. At present. variations in terrestrial chemical erosion appear to have only a reduced impact on (CO2)-C-atms and only little influence on the global Si and Ge cycle and marine Ge/Si ratios during deglaciation. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailGlacial-interglacial changes of continental weathering: estimates of the related CO2 and HCO3- flux variations and their uncertainties
Munhoven, Guy ULg

in Global and Planetary Change (2002), 33(1-2), 155-176

A range of estimates for the glacial-interglacial variations in CO, consumption and HCO3- production rates by continental weathering processes were calculated with two models of continental weathering ... [more ▼]

A range of estimates for the glacial-interglacial variations in CO, consumption and HCO3- production rates by continental weathering processes were calculated with two models of continental weathering: the Gibbs and Kump Weathering Model (GKWM) [Paleoceanography 9(4) (1994) 529] and an adapted version of Amiotte Suchet and Probst's Global Erosion Model for CO2 Consumption (GEM-CO2) [C. R, Acad. Sci. Paris, Ser. 11317 (1993) 615; Tellus 47B (1995) 273]. Both models link CO2 consumption and HCO3- production rates to the global distributions of lithology and runoff. A spectrum of 16 estimates for the runoff distribution at the Last Glacial Maximum (LGM) was constructed on the basis of two different data sets for present-day runoff and climate results from eight GCM climate simulation experiments carried out in the framework of the Paleo Modelling Intercomparison Project (PMIP). With these forcings, GKWM produced 3.55-9.0 Tmol/year higher and GEM-CO2 4.7-13.25 Tmol/year higher global HCO3- (1 Tmol=10(12) mol) production rates at the LGM, Mean variations (plus/minus one standard error of the mean with 7 df) were 6.2+/-0.6 and 9.4+/-1.0 Tmol/year, respectively. The global CO2 consumption rates obtained with GKWM were 1.05-4.5 Tmol/year (mean: 2.8+/-0.4 Tmol/year) higher at the LGM than at present. With GEM-CO2 this increase was 1.95-7.15 Tmol/year (mean: 4.8+/-0.6 Tmol/year). The large variability in the changes obtained with each weathering model was primarily due to the variability in the GCM results. The increase in the CO2 consumption rate due to continental shelf exposure at the LGM was always more than 60% larger than its reduction due to ice cover. For HCOT production rates, the increase related to shelf exposure was always more than twice as large as the decrease due to ice cover. Flux variations in the areas exposed both now and at the LGM were, in absolute value, always more than 3.5 times lower than those in the shelf environment. The calculated CO2 consumption rates by carbonate weathering were consistently higher at the LGM, by 2.45-4.5 Tmol/year (mean: 3.4+/-0.2 Tmol/year) according to GKWM and by 2.75-6.25 Tmol/year (mean: 4.6+/-0.4 Tmol/year) according to GEM-CO, For silicate weathering, GKWM produced variations ranging between a 1.9 Tmol/year decrease and a 0.4 Tmol/year increase for the LGM (mean variation: -0.7+/-0.2 Tmol/year); GEM-CO, produced variations ranging between a 0.8 Tmol/year decrease and a 1.05 Tmol/year increase (mean variation: +0.2+/-0.2 Tmol/year). In the mean, the calculated variations of CO2 and HCO3- fluxes would contribute to reduce atmospheric p(CO2) by 5.7+/-1.3 ppmv (GKWM) or 3 12.1+/-1.7 ppmv (GEM-CO2), which might thus represent a non-negligible part of the observed glacial interglacial variation of similar to 75 ppmv. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailAtmospheric CO2 consumption by continental erosion: present-day controls and implications for the last glacial maximum
Ludwig, Wolfgang; Amiotte-Suchet, Philippe; Munhoven, Guy ULg et al

in Global and Planetary Change (1998), 16-17

The export of carbon from land to sea by rivers represents a major link in the global carbon cycle, For all principal carbon forms, the main factors that control the present-day fluxes at the global scale ... [more ▼]

The export of carbon from land to sea by rivers represents a major link in the global carbon cycle, For all principal carbon forms, the main factors that control the present-day fluxes at the global scale have been determined in order to establish global budgets and to predict regional fluxes. Dissolved organic carbon fluxes are mainly related to drainage intensity, basin slope, and the amount of carbon stored in soils. Particulate organic carbon fluxes are calculated as a function of sediment yields and of drainage intensity. The consumption of atmospheric/soil CO2 by chemical rock weathering depends mainly on the rock type and on the drainage intensity. Our empirical models yield a total of 0.721 Gt of carbon (Gt C) that is exported from the continents to the oceans each year. From this figure, 0.096 Gt C come from carbonate mineral dissolution and the remaining 0.625 Gt C stem from the atmosphere (F-CO2). Of this atmospheric carbon, 33% is discharged as dissolved organic carbon, 30% as particulate organic carbon, and 37% as bicarbonate ions. Predicted inorganic carbon fluxes were further compared with observed fluxes for a set of 35 major world rivers, and possible additional climatic effects on the consumption of atmospheric CO2 by rock weathering were investigated in these river basins. Finally, we discuss the implications of our results for the river carbon fluxes and the role of continental erosion in the global carbon cycle during the last glacial maximum. [less ▲]

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See detailModelling the glacial-interglacial changes in the continental biosphere
François, Louis ULg; Delire, Christine; Warnant, Pierre ULg et al

in Global and Planetary Change (1998), 17

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to ... [more ▼]

A new estimate of the glacial-interglacial variations of the terrestrial carbon storage was obtained with the CARAIB biosphere model. The climatic data for the Last Glacial Maximum (LGM) necessary to drive the biosphere model are derived from results of the ECHAM2 General Circulation Model (GCM). Six model simulations (four under typical interglacial and two under typical glacial climatic conditions) were performed to analyse the roles of different environmental changes influencing the biospheric net primary productivity (NPP) and carbon stocks. The main differences between these simulations come from the adopted CO, levels in the atmosphere, the presence or absence of crops and from changing continental boundaries. The variation of the terrestrial carbon stocks since the LGM are estimated by comparing the pre-agricultural (280 ppm of CO2, no crops, modern climate) and the full glacial simulations (200 ppm of CO2, LGM climate reconstruction). Our model predicts a global NPP increase from 38 Gt C year(-1) to 53 Gt C year(-1) during the deglaciation, a substantial part of that change being due to CO, fertilization. At the same time, the terrestrial biosphere would have fixed between 134 (neglecting CO2 fertilization effects) and 606 Gt C. The treatment of both the C-3 and C-4 photosynthetic pathways in the CARAIB model enabled us further to reconstruct the partitioning between C, and C, plants. Following our experiments, 29.7% of the total biospheric carbon stock at the LGM was C-4 material, compared to an interglacial fraction of only 19.8%. The average biospheric fractionation factor was similar to 1.5 parts per thousand less negative at LGM than it is today. Considering an atmospheric delta(13)C 0.5 +/- 0.2 parts per thousand lower at LGM than at pre-industrial times, the 606 Gt C transfer would lead to a global ocean delta(13)C shift of roughly -0.41 parts per thousand, fully consistent with currently available data. For the smaller change of 134 Gt C obtained without the CO2 fertilization effect, this shift would only be on the order of -0.10 parts per thousand. (C) 1998 Elsevier Science B,V. All rights reserved. [less ▲]

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See detailThe faint young sun climatic paradox: Influence of the continental configuration and of the seasonal cycle on the climatic stability
Longdoz, Bernard; François, Louis ULg

in Global and Planetary Change (1997), 14(3-4), 97-112

A quasi-three-dimensional climate model is used to study the early state of the Earth when the solar luminosity was 70% of the present value, Usually, climatic simulations going back to this period lead ... [more ▼]

A quasi-three-dimensional climate model is used to study the early state of the Earth when the solar luminosity was 70% of the present value, Usually, climatic simulations going back to this period lead to a completely frozen planet contrasting with the geologic evidences of sedimentary rock formation and thus of the presence of liquid water at the surface of the continents during the Archean (4.6-2.5 billion years before present). Here, several model simulations are performed for solar luminosities varying between 0.7 and 1 times the present value. Using the present-day continental configuration and taking the seasonal cycle into account, a steady state is found in which glaciation is complete but snow covers only some oceanic coasts, leaving the continents essentially snow-free. As a result, the albedo of the continental area is strongly reduced compared to that of the frozen ocean, Some continental temperatures can almost reach the freezing point of water in summer (-1 degrees C in the center of Eurasia). This result can be explained by the behavior of the detailed hydrologic cycle included in the model. During the decrease of the solar luminosity, the jump to a completely frozen Earth occurs when the solar luminosity reaches 0.86 times its present value. The behavior of the climatic system is substantially different with a global ocean configuration. In the absence of land surfaces, the meridional heat transport, explicitly calculated, is less effective and the glaciation of a model latitude zone does not lead to the glaciation of its equatorward neighbor. The climate instability is relatively local and the jump to the completely frozen state is much more progressive than in the case of the modem continental configuration. The role of the seasonal cycle in the paleoclimatic simulation is also studied. Due to the non-linearity of the model, removing the seasonal cycle drives the system to an increase of the annual mean planetary albedo and to a decrease of the relative value (0.82) of the critical solar luminosity at which the jump to the completely frozen solution occurs. [less ▲]

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See detailThe faint young sun climatic paradox: A simulation with an interactive seasonal climate-sea ice model
Gérard, Jean-Claude ULg; Hauglustaine, Didier A.; François, Louis ULg

in Global and Planetary Change (1992), 97(3), 133-150

A seasonal one-and-a-half-dimensional (1 1/2-D) energy-balance climate model including a detailed sea ice calculation and an interactive albedo formulation has been developed and is used to investigate ... [more ▼]

A seasonal one-and-a-half-dimensional (1 1/2-D) energy-balance climate model including a detailed sea ice calculation and an interactive albedo formulation has been developed and is used to investigate the faint young sun climatic paradox. This model is shown to reproduce the present climate and sea ice observations. In spite of its greater complexity, its behavior is globally similar to simple energy-balance models with highly parameterized ice-albedo feedback used in previous studies of this question. It is found that when the solar luminosity drops by more than about 5% below its present value, the ice albedo feedback causes a global irreversible glaciation. Several sensitivity experiments show that the value of the critical solar constant and associated global surface temperature are only little sensitive to the set of model parameters describing the ice and snow albedo and meridional heat transport. In contrast, the absence or polar location of the continental mass introduce a nearly 10% decrease of the critical luminosity. The minimum level of atmospheric CO2 needed to prevent a global glaciation through enhanced greenhouse warming is calculated as a function of the solar luminosity. A 30% drop in solar output requires a 2 x 10(4)-fold increase in atmospheric CO2, an unacceptably large value. However, in the absence of continents, a carbon dioxide partial pressure of 2000 times the present level is found to be sufficient to stabilize the climate. The effects of a reduced continental area, paleogeographic changes and higher CO2 greenhouse effect combine to ensure a larger stability of the non-frozen configuration. Their cumulated and interactive effects may be able to solve the young sun paradox. [less ▲]

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See detailA sensitivity study of the role of continental area and location on Paleozoic climate
Hauglustaine, Didier A.; Gérard, Jean-Claude ULg

in Global and Planetary Change (1992), 97

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