The study of past climate is important because it increases our understanding of how the climate system works. Past climate is often reconstructed by using proxies (that is observations of things that tell something about past climate, for example tree rings, pollen in lake sediments and fossils). Model simulations of past climate further increases the knowledge since it has the possibility to gap the space and time between the sparse and scattered proxy observations, since a model simulation gives relatively continuous information about the whole simulated area. Model simulations can also give internally coherent information about parameters that is not easily reconstructed from proxies (for example heat fluxes).  In this thesis two periods in the past are simulated by climate models: the Marine Isotope Stage 3 (MIS 3), 44 000 years ago, and the Last Glacial Maximum (LGM), 21 000 years ago. Both periods are characterised by low temperature, low sea level and low level of carbon dioxide. The topography in northern Europe is dominated by ice sheets covering Iceland, Norway and parts of Sweden at MIS3; and more extensive ice sheets covering Iceland, Scandinavia, the British Isles and Northern Germany at LGM. These periods are firstly simulated by a global climate model. Those simulations are subsequently used in a regional climate model to increase the level of detail over Europe. To make the regional climate model simulation more realistic vegetation simulated by a dynamical vegetation model is used in the regional climate model.   The climate models simulate European climates much colder than today, especially at LGM. The temperature differences ranges from 5 to 45 °C colder than today; the largest differences being at the ice sheets where the perennial ice cover and the high altitude keep temperatures low. Precipitation is reduced with as much as almost 100 % in northern Europe due to reduced evaporation. Precipitation is increased with as much as 100 % in parts of southern Europe due to changes in atmospheric circulation. The simulations are in broad agreement with proxies, although there are differences.  The vegetation model simulates tundra like vegetation (herbs and shrubs) in the ice-free parts of central and southern Europe. The eastern parts of Europe are dominated by needle-leaved trees. The short and cool summers limit vegetation. The simulated vegetation is in broad agreement with reconstructions. Sensitivity studies of vegetation show that changed vegetation can change the monthly mean temperature with 1-3 °C in some seasons and regions. The response depends on regional surface characteristics. Sensitivity studies of ice sheets show that the simulated climate is consistent with the assumptions about the ice sheet extent made in the simulation. The simulated climate is cold enough in northern Europe to support the ice sheet, and warm enough in southern Europe to prevent the ice sheet from expanding in this direction. A removal of the ice sheet would only have an effect on the local scale in the vicinity of the ice sheet, but this experiment did not include changes in the large-scale global atmospheric circulation.  Although the regional climate model simulations are to a large degree depending on the global climate model simulations they provide new information. When comparing proxies with model data or studying local/regional climatic features (such as the interplay between climate and vegetation) high horizontal resolution, as in the regional climate model, is important. / Studiet av klimat i det förgångna är viktigt eftersom det ökar vår förståelse för hur klimatsystemet fungerar. Förgånget klimat rekonstrueras ofta med hjälp av proxies (det vill säga observationer av saker som säger något om klimatet förr i tiden, till exempel trädringar, pollen i sjösediment och fossiler). Modellsimuleringar av förgånget klimat ökar kunskapen ytterligare eftersom det ger en möjlighet att fylla i luckorna, i tid och rum, mellan de glesa och spridda proxy-observationerna, eftersom en modellsimulering ger information om hela det simulerade området. Modellsimuleringar kan också ge information om parametrar som inte så lätt rekonstrueras från proxies (till exempel värmeflöden).   I denna avhandling simuleras med klimatmodeller två perioder i det förgångna: MIS 3 (Marine Isotope Stage 3), för 44 000 år sedan och LGM (Last Glacial Maximum), för 21 000 år sedan. Båda perioderna kännetecknas av låg temperatur, låg havsnivå och låg halt av koldioxid. Topografin i norra Europa domineras av istäcken som täcker Island, Norge och Sverige vid MIS 3; och istäcken över Island, Skandinavien, Brittiska öarna och norra Tyskland vid LGM. Dessa perioder simuleras först av en global klimatmodell. Simuleringarna används senare i en regional klimatmodell för att öka detaljgraden över Europa. För att göra den regionala klimatmodell-simuleringen mer realistisk så används i den regionala klimatmodellen vegetation som är simulerad av en dynamisk vegetationsmodell. Klimatmodellerna simulerar europeiska klimat som är mycket kallare än dagens, särskilt vid LGM. Temperaturdifferensen spänner från 5 till 45 °C kallare än idag; de största skillnaderna är vid istäckena där det ständiga istäcket och den höga altituden håller temperaturen nere. Nederbörden minskar med så mycket som nästan 100 % i norra Europa på grund av minskad avdunstning. Nederbörden ökar med så mycket som 100 % i delar av södra Europa på grund av förändringar i atmosfärens cirkulation. Simuleringarna stämmer i stora drag överens med proxies, även om det finns skillnader.  Vegetationsmodellen simulerar tundralik vegetation (örter och snår) i de isfria delarna av centrala och södra Europa. De östra delarna av Europa domineras av barrträd. De korta och kalla somrarna begränsar vegetationen. Den simulerade vegetationen stämmer i stora drag överens med rekonstruktionerna. Känslighetsstudier av vegetationen visar att förändrad vegetation kan förändra månadsmedeltemperaturen med 1-3 °C i vissa regioner och under vissa säsonger. Responsen beror på regionala egenskaper vid markytan. Känslighetsstudier av istäckena visar att det simulerade klimatet är förenligt med de antaganden av istäckenas utbredning som görs i simuleringen. Det simulerade klimatet är tillräckligt kallt i norra Europa för att göra ett istäcke möjligt, och tillräckligt varmt i södra Europa för att hindra istäcket från att växa i den riktningen. Om istäcket skulle tas bort skulle det bara ha en effekt på lokal skala i närheten av istäcket, men detta experiment innefattade inte förändringar i atmosfärens cirkulation. Även om de regionala klimatmodell-simuleringarna till stor del beror på de globala klimatmodell-simuleringarna så ger de ny information. Vid jämförelser av proxies och modelldata eller studier av lokala/regionala egenskaper hos klimatet (som växelverkan mellan klimat och vegetation) så är hög horisontell upplösning, som i en regional klimatmodell, viktigt.

Les enregistrements climatiques globaux à l’échelle géologique entre le Crétacé et le début du Cénozoïque indiquent des variations de grande amplitude. Sur le long terme, celles-ci sont déterminées par l’équilibre entre la composition atmosphérique en gaz à effet de serre, principalement le CO2, issus du dégazage volcanique et l’altération continentale, modulée par les mouvements tectoniques des continents. Dans cette thèse, les liens entre paléogéographie et CO2 ont été étudiés dans le contexte des interactions entre climat et calottes de glace au cours d’un intervalle de temps dit de « greenhouse », entre 120 et 34 Ma. L’utilisation d’une suite de modèles impliquant un modèle couplé moyenne résolution, un modèle atmosphérique haute résolution et un modèle de calotte de glace, a permis de montrer que les changements paléogéographiques survenant au Crétacé ont régulé la présence de glace en Antarctique. Dans un second temps, une nouvelle méthode de couplage climat-calotte a été développée pour étudier la glaciation Eocène-Oligocène. Ces développements ont permis de reconstruire une évolution fidèle de celle-ci, en bon accord avec les données. Deux rétroactions liées à cette glaciation et à la chute concomitante du CO2 atmosphérique sont étudiées. En premier lieu, l’impact de la glaciation sur le Courant Circumpolaire Antarctique est abordé, montrant que celle-ci génère une intensification de ce courant. Ensuite, au sein d’une étude mêlant données et modèles pour documenter la présence de moussons en Asie dès l’Eocène moyen, il est montré que le changement climatique de la fin de l’Eocène induit une baisse d’intensité de la mousson asiatique. Enfin, dans la perspective d’analyser les conséquences des changements paléogéographiques du Cénozoïque sur la biogéochimie marine, des tests de sensibilité aux passages océaniques de Panama et de Drake ont été réalisés. / On geological timescales, global climate proxies indicate that variations of large magnitude occur between the Cretaceous and the Cenozoic. On the long term, these variations are mostly determined by the equilibrium between the greenhouse gases composition of the atmosphere, primarily the CO2, and continental weathering set up by the spatial location of Earth’s landmasses. Here, the links between paleogeography and CO2 are looked upon in a climate-ice sheet interactions framework during a greenhouse period of Earth history (120 – 34 Ma). A suite of models involving both coupled and ice sheet models have been used to demonstrate that paleogeographic reorganizations have regulated the presence of ice over Antarctica during the Cretaceous. In a second time and using a similar setup, a new method for climate-ice sheet coupling have been developed and applied to the Eocene-Oligocene (EO) glaciation to yield a new scenario of ice evolution, in good agreement with data. Two feedbacks related to this glaciation and the coeval atmospheric CO2 fall are investigated. First, it is shown that the EO glaciation generates an intensification of the Antarctic Circumpolar Current. Second, within a data-model study demonstrating active Asian monsoons as old as the mid-Eocene, it is shown that the climatic change at the end of the Eocene is responsible for a reduction in the intensity of the Asian monsoon. Finally, with the aim of analysing the effect of paleogeographic changes on marine biogeochemistry during the Cenozoic, sensitivity tests to Drake Passage and Panama Seaway have been carried out.

ROCKE-3D is a contemporary Global Circulation Model allowing research into the complex processes behind the climate of planets. Using ROCKE-3D one can construct a model coupling atmosphere, land, and ocean revealing how the climate of a planet evolves over time. When constructing a model using ROCKE-3D, 2 different types of oceans can be used, one shallow without horizontal heat transfer and one fully coupled dynamic ocean. Simulations created using the different ocean types give rise to different results. In this project, the fractional habitability of the model 'planets' will be calculated using various methods in order to evaluate the differences between ocean types in ROCKE-3D simulations. There is also a hope to better understand how parameters such as rotation period and insolation, are affected when using different ocean types. The results show a large difference in predicted habitability fraction using two approximations for the ocean heat transport indicating that the Qflux approximation produces unrealistic models and should be avoided. / ROCKE-3D är en modern Global Circulation Model som tillåter forskning in i de komplexa processer som bygger planeters klimat. Vid användning av ROCKE-3D kan modeller som kopplar atmosfärer, land och hav konstrueras, detta kan avslöja hur en planets klimat utvecklas över tid. När en model konstrueras med ROCKE-3D kan 2 olika typer av hav användas, ett utan horisontell värmeöverföring som kallas för ett "Qflux" hav och ett fullt kopplat dynamiskt hav. Simulationer skapade med de olika havstyperna ger skillnad i resultat. I det här projektet, beräknas modell-planeternas fractional habitability för att evaluera skillnaden mellan havstyp i ROCKE-3D simulationer. Det finns även ett hopp för en bättre förståelse av hur parametrar, rotationsperiod och solinstrålning, påverkar när det är att föredra användningen av en viss havstyp. Resultaten visar att skillnaden i ""fractional habitability" mellan simulationer skapta med de 2 havstyperna minskar när solinstrålningen ökar, vilket visar att användandet av ett "Qflux" hav i skapandet av simulationer vid låg solinstrålning borde avrådas.

With the acceleration of climate change, mitigating climate impacts in all aspects of society is key to ensuring a sustainable development. The building sector is responsible for a major share of global carbon emissions, and in Sweden about a fifth of national greenhouse gas emissions derive from the different stages of building operations. Currently, there are legal requirements concerning sustainability reports for organisations’ overall operations within the sector, and climate impact calculations for new productions and building materials are also common. However, for facility management services, which include for example service and administration connected to properties, there are no systematic methods for calculating the climate impacts in detail.  Riksbyggen is a Swedish cooperative company operating within the building sector and provides, amongst other things, facility management services to tenant-owned cooperatives and commercial customers. They conduct sustainability reports annually but have not yet evaluated the climate impacts from facility management services. The aim of this study is therefore to construct a model for calculating and allocating climate impacts to Riksbyggen’s facility management service supply. Employing a mixed-method approach, including a literature review, interviews and data collection, a model for allocating climate impacts is proposed. The model design consists of three steps: compilation of climate impact data, mapping of facility management services as well as an allocation procedure.  Applying the model to Riksbyggen’s climate impact figures in 2019, this study finds three facility management services (Regularly cleaning, Remedial maintenance and Bonum) with significantly large climate impacts. With the climate impact figures from 2020 published during the process of this study, the model is once again applied and provides a comparison between the two years, showcasing a slight difference in the distribution across the service supply. The findings further show that transports play a central part in how the climate impacts per service vary. Therefore, one sensitivity analysis and two scenarios relating to transport activities are conducted, corroborating the significant influence of transports on the climate impact figures per service.  Future applications of the model include incorporating the modelling results into maintenance planning, annual reports and product sheets, both for the case of Riksbyggen as well as other organisations. Furthermore, the climate impact figures can possibly work as a supporting element for tracking the progress of the SBTi within facility management organisations. Finally, potential uncertainties with the model design are addressed, as well as relevant future additions to improve the accuracy of the results. / Med klimatförändringarnas framfart är det allt viktigare att minska klimatpåverkan i alla delar av samhället för att möjliggöra en hållbar utveckling. Byggsektorn står idag för en markant del av de globala koldioxidutsläppen, och i Sverige härstammar en femtedel av de nationella växthusgasutsläppen från olika delar av byggskedet. I nuläget finns det lagkrav kring hur företag inom sektorn ska rapportera sin klimatpåverkan från dess övergripande verksamhet i hållbarhetsredovisningar, och det är även vanligt med beräkningar av klimatpåverkan från nyproduktioner och byggmaterial. För förvaltningstjänster, som inkluderar exempelvis service och administration kopplat till fastigheter, finns däremot inget systematiskt tillvägagångssätt att beräkna klimatpåverkan på detaljnivå.  Riksbyggen är ett svenskt kooperativt företag som arbetar inom byggsektorn och bland annat erbjuder förvaltningstjänster till bostadsrättsföreningar samt kommersiella kunder. De rapporterar sin klimatpåverkan i årliga hållbarhetsredovisningar, men har ännu inte en metod för att beräkna klimatpåverkan för varje förvaltningstjänst. Målet med denna studie är därför att bygga en modell för att beräkna och allokera klimatpåverkan från Riksbyggens förvaltningstjänster. Genom att tillämpa en kombination av kvalitativa och kvantitativa metoder, såsom litteraturstudie, intervjuer samt datainsamling, föreslås en modell för att allokera klimatpåverkan. Modellstrukturen innehåller tre steg; sammanställning av klimatdata, kartläggning av förvaltningstjänster samt ett allokeringssteg.  Genom att applicera modellen på Riksbyggen klimatdata från 2019 visar denna studie att tre tjänster från utbudet av förvaltningstjänster (Regelmässig städning, Avhjälpande underhåll och Bonum) har särskilt hög klimatpåverkan. Under projektets gång publicerade Riksbyggen sin klimatdata från 2020. Därmed appliceras modellen även på 2020 och tyder på skillnader i distributionen av klimatpåverkan mellan de två åren. Studien visar även att transporter har en betydande roll för hur klimatpåverkan varierar mellan de olika tjänsterna. Därför genomförs en känslighetsanalys samt två scenarion relaterade till transporter, som stärker slutsatsen att transporter spelar en stor roll för respektive tjänsts klimatpåverkan.  Framtida tillämpningsområden för modellen inkluderar att använda siffrorna för klimatpåverkan per förvaltningstjänst i underhållsplaner, årsredovisningar samt produktblad, både för fallstudien Riksbyggen men även för andra organisationer som arbetar med fastighetsförvaltning. Utöver detta kan modellen potentiellt fungera som ett stöd för att mäta framstegen inom The Science Based Targets initative (SBTi). Till sist adresseras möjliga osäkerheter i modellen, samt relevanta tillägg för att i framtiden kunna förbättra noggrannheten av resultaten.

In this study, theorem-based, generally applicable stochastic parameterisation schemes are developed and applied to a quasi-geostrophic model of extratropical atmospheric low-frequency variability (LFV). Hasselmann’s method is developed from limiting theorems for slow-fast systems of ordinary differential equations (ODEs) and applied to this high-dimensional model of intermediate complexity comprised of partial differential equations (PDEs) with complicated boundary conditions. Seamless, efficient algorithms for integrating the parameterised models are developed, which require only minimal changes to the full model algorithm. These algorithms may be readily adapted to a range of climate models of greater complexity in parameterising the effects of fast, sub-grid scale processes on the resolved scales. For comparison, the Majda-Timofeyev-Vanden-Eijnden (MTV) parameterisation method is applied to this model. The seamless algorithms are first adapted to probe the multiple regime behaviour that characterises the full model LFV. In contrast to the conclusions of a previous study, it is found that the multiple regime behaviour is not the result of a nonlinear interaction between the leading two planetary-scale modes, but rather is the result of interactions among these two modes and the leading synoptic-scale mode. The low-dimensional Hasselmann stochastic models perform well in simulating the statistics of the planetary-scale modes. In particular, a model with only one resolved (planetary-scale) mode captures the multiple regime behaviour of the full model. Although a fast-evolving synoptic-scale mode is of primary importance to the multiple regime behaviour, deterministic averaged forcing and not multiplicative noise is responsible for the regime behaviour in this model. The MTV models generate non-Gaussian statistics, but generally do not perform as well in capturing the climate statistics.

A statistical downscaling technique is employed to link atmospheric circulation produced by climate models at the large-scale to precipitation recorded at individual weather stations on Vancouver Island. Relationships between the different spatial scales are established with synoptic typing, coupled with non-homogeneous Markov models to simulate precipitation intensity and occurrence in historical and future periods. Types are generated through a clustering algorithm which processes daily precipitation observations recorded by Environment Canada weather stations spanning 1971 to 2000. Large-scale atmospheric circulation data is taken from an ensemble of climate model projections made under the IPCC AR4 SRES A2 scenario through the end of the 21st century. Atmospheric predictors used to influence the Markov model are derived from two versions of the data: Averages of model grid cells selected by correlation maps of circulation and precipitation data; a new approach involving Common Empirical Orthogonal Functions (EOFs) calculated from model output over the Northeast Pacific Ocean. Circulation-based predictors capture the role of sea level pressure (SLP), and winds in influencing coastal precipitation over Vancouver Island. The magnitude and spatial distribution of the projected differences are dependent on the predictors used. Projections for 2081 to 2100 made using common EOFs result in most stations reporting no statistically significant change compared to the baseline period (1971 to 2000) in both seasons. Projections using averaged grid cells find winter season (Nov-Feb) precipitation anomalies produce values that are modestly positive, with typical gains of 6.5% in average precipitation, typical increases of 7.5% rising up to 15% in extreme precipitation, and little spatial dependence. In contrast, average and extreme summer precipitation intensity (Jun-Sep) declines negligibly at most island weather stations with the exception of those on the southern and western sections, which experience reductions of up to 20% relative to the latter thirty years of the twentieth century. Precipitation occurrence decreases slightly in both seasons at all stations with declines in the total days with measurable precipitation ranging from 2% to 8% with reductions also seen in the length of extended periods of precipitation in both seasons.

Exoplanet discovery has grown more quickly in recent years. However, the nature of their discovery leaves many unanswered in questions regarding exoplanetary habitability. Proxima Centauri b, an exoplanet which orbits the Sun's closest stellar neighbour, Proxima Centauri, was recently discovered with a subzero equilibrium temperature. Although not considered habitable based on the classical definition of the liquid water range, there may be fractions of Proxima Centauri b which are habitable. A prior study simulated the climate conditions of Proxima Centauri b until equilibrium was reached, using a variety of initial conditions. In this project, various metrics for calculating the fractional habitability of Proxima Centauri b are presented and applied to the results of the prior study's simulations. Colormaps are used to show the ice and temperature distributions that produce the calculated values of fractional habitability. The fractional habitabilities calculated show that while the value is both case and metric dependent, for the vast majority of all cases and metrics the value is nonzero implying that Proxima Centauri b is likely to have habitable regions. / Upptäckandet av exoplaneter har ökat i takt över de senaste åren. Samtidigt, på grund av sättet som de upptäcks finns många obesvarade frågor angående planeternas beboelighet. Proxima Centauri b är en exoplanet som kretsar kring solens närmsta granne, Proxima Centauri. Exoplaneten upptäcktes nyligen med en jämviktstemperatur under $0\degree$C. Trots att exoplaneten inte anses beboelig enligt klassisk definition kan det finnas delar av Proxima Centauri b som är beboeliga. En tidigare studie simulerade klimatförhållandena av Proxima Centarui b till jämvikt nåddes, med varierade begynnelsetillstånd. I detta projekt beräknas andelen av Proxima Centauri b som är beboelig genom flera olika mått för "fractional habitability". Måtten jämförs med den tidigare studien och dess simuleringar. Grafiskt åsikdligörs resultaten via färgkartor över planeten för istjocklek och yttemperatur. De beräknade värdena på Proxima Centauri b's "fractional habitability" påvisar beroende på mått och begynnelsetillstånd. Däremot, för en majoritet av både fall och mått är värdet nollskilt vilket antyder att Proxima Centauri b är delvist beboelig.

Current climate models often predict fractional cloud cover on the basis of a diagnostic probability density function (PDF) describing the subgrid-scale variability of the total water specific humidity, qt, favouring schemes with limited complexity. Standard shapes are uniform or triangular PDFs the width of which is assumed to scale with the gridbox mean qt or the grid-box mean saturation specific humidity, qs. In this study, the qt variability is analysed from large-eddy simulations for two stratocumulus, two shallow cumulus, and one deep convective cases. We find that in most cases, triangles are a better approximation to the simulated PDFs than uniform distributions. In two of the 24 slices examined, the actual distributions were so strongly skewed that the simple symmetric shapes could not capture the PDF at all. The distribution width for either shape scales acceptably well with both the mean value of qt and qs, the former being a slightly better choice. The qt variance is underestimated by the fitted PDFs, but overestimated by the existing parameterisations. While the cloud fraction is in general relatively well diagnosed from fitted or parameterised uniform or triangular PDFs, it fails to capture cases with small partial cloudiness, and in 10 – 30% of the cases misdiagnoses clouds in clear skies or vice-versa. The results suggest choosing a parameterisation with a triangular shape, where the distribution width would scale with the grid-box mean qt using a scaling factor of 0.076. This, however, is subject to the caveat that the reference simulations examined here were partly for rather small domains and driven by idealised boundary conditions.

The Earth's climate system is driven by varying insolation from the Sun. The dominant variations in insolation are at 23 and 40 thousand year periods, yet for the past million years the Earth's climate has glacial cycles at approximately 100 kyr periodicity. These cycles are a coupled variation in temperature, ice volume, and atmospheric CO₂. Somehow the Earth system's collective response to 23 and 40 kyr insolation forcing produces 100 kyr glacial-interglacial cycles. Generally it has been assumed that the causative mechanisms are a combination of ice dynamics (high ice reflectivity controlling temperature) and ocean circulation (changing carbon partitioning between the deep ocean and the atmosphere, and heat transport to the poles). However, these proposed mechanisms have not yet resulted in a compelling theory for all three variations, particularly CO₂. This thesis explores the role of volcanic CO₂ emissions in glacial cycles. I calculate that glacial-driven sea level change alters the pressure on mid-ocean ridges (MORs), changing their CO₂ emissions by approximately 10%. This occurs because pressure affects the thermodynamics of melt generation. The delay between sea level change and the consequent change in MOR CO₂ emissions is several tens-of-thousands-of-years, conceptually consistent with a coupled non-linear oscillation that could disrupt glacial cycles from a 40 kyr mode to a multiple of that period. I develop an Earth system model to investigate this possibility, running for approximately one million years and explicitly calculating global temperatures, ice sheet configuration, and CO₂ concentration in the atmosphere. The model is driven by insolation, with all other components varying in response (and according to their own interactions). This model calculates that volcanism is capable of causing a transition to ̃100 kyr glacial cycles, however the required average volcanic CO₂ emissions are barely within the 95% confidence interval. Therefore it is possible for volcanic systems and glacial cycles to form a 100 kyr coupled oscillation.

Le Bilan de Masse de Surface (BMS, c'est-à-dire les précipitations de neige auxquelles est retranchée l'ablation par sublimation, ruissellement ou érosion) de la calotte polaire Antarctique représente une contribution majeure et encore mal connue à l'évolution actuelle du niveau des mers. Le stockage d'eau douce par accumulation de neige sur la calotte posée est supposé s'intensifier au cours du 21eme siècle, modérant l'élévation du niveau des mers et modifiant la dynamique glaciaire. Les trois-quarts du bilan de masse de surface Antarctique sont concentrés au dessous de 2000 m d'altitude alors que cette zone ne représente que 40% de la surface de la calotte posée. Les précipitations orographiques sont une contribution majeure à l'accumulation dans cette région, il est donc crucial d'estimer précisément ce terme. La modélisation de ce processus est fortement dépendant de la résolution des modèles, car les pentes de la calotte influencent l'intensité des précipitations orographiques. La sublimation et la fonte de la neige sont eux aussi fortement dépendant de l'élévation. Bien qu'ils contribuent actuellement peu au bilan de masse de surface de l'Antarctique, ils sont susceptibles de subir des changements importants au cours des prochains siècles. Les modèles atmosphériques de climat, globaux ou régionaux, ne peuvent pas atteindre une résolution allant au delà de 40 km sur l'Antarctique pour des simulations à l'échelle du siècle du fait de coûts de calcul importants. A ces résolutions, la topographie des zones côtières Antarctique n'est pas correctement représentée. C'est pourquoi nous avons développé le modèle de régionalisation SMHiL (Surface Mass balance High-resolution downscaLing) qui permet d'estimer les composantes du bilan de masse de surface Antarctique à haute résolution (~15 km) à partir de champs atmosphériques de plus grande échelle. Nous calculons l'effet de la topographie fine sur les précipitations orographiques et sur les processus de couche limite menant à la sublimation, la fonte et le regel. SMHiL est validé pour la période actuelle à partir d'un jeu de données inédit constitué de plus de 2700 observations de qualité contrôlée. Cependant, les observations représentatives du BMS de la zone côtière Antarctique y sont sous-représentées. Dans ce contexte, nous montrons que la ligne de balise mise en place par l'observatoire GLACIOCLIM-SAMBA en bordure de calotte constitue une référence pour estimer les performances des modèles. Enfin, nous utilisons SMHiL à l'aval du modèle de circulation générale LMDZ4 pour évaluer les variations de BMS au cours du 21eme et du 22eme siècles. Le BMS à haute résolution est significativement différent de celui de LMDZ4 et est plus proche du BMS observé pour la période actuelle. Les résultats suggèrent que les précédentes estimations d'augmentation du BMS au cours du prochain siècle étaient sous-estimées de près de 30% par LMDZ4. Les changements de BMS à faible élévation résulteront d'une compétition entre l'augmentation d'accumulation de neige et de ruissellement. SMHiL est un outil destiné à être appliqué à l'aval d'autres modèles de climat, globaux ou régionaux, pour une meilleure estimation des variations futures du niveau des mers. / The Antarctic Surface Mass Balance (SMB, i.e. the snow accumulation from which we subtract ablation by sublimation, run-off or erosion) is a major yet badly known contribution to changes in the present-day sea level. Water storage by snow accumulation on the Antarctic continent is expected to increase in the 21st century, which would moderate the rise in sea level and impact the ice dynamic response of the ice sheet. Three-quarters of the Antarctic SMB are concentrated below 2000 m above sea level whereas this area represents only 40% of the grounded ice sheet area. Orographic precipitation is a major contributor to snow accumulation in this region, which is why a better estimation of this term is important. The representation of this process by models depends to a great extent on the resolution of the model, since precipitation amounts depend on the ice sheet slopes. Sublimation and snowmelt also depend on elevation, and although they are presently minor contributors to the Antarctic SMB, their role is expected to become more important in the coming centuries. Global and regional atmospheric climate models are unable to achieve a 40-km resolution over Antarctica at a century time scale, due to their computing cost. At this resolution, the Antarctic coastal area is still badly represented. This is why we developed the downscaling model SMHiL (Surface mass balance high-resolution downscaling) to estimate the Antarctic SMB components at a high resolution (~15 km) from large-scale atmospheric forcings. We computed the impact of the high-resolution topography on orographic precipitation amounts and the boundary layer processes that lead to sublimation, melting and refreezing. SMHiL has been validated for the present period with a dataset composed of more than 2700 quality-controlled observations. However, very few of these observations are representative of the Antarctic coastal area. In this context, we show that the GLACIOCLIM-SAMBA stake lines located on the ice sheet coast-to-plateau area is an appropriate reference to evaluate model performance. Finally, we used SMHiL to estimate the SMB changes during the 21st and 22nd centuries, by downscaling the atmospheric global climate model LMDZ4. The high-resolution SMB is significantly different from the SMB given by LMDZ4 and is closer to the observed one for the present period. Our results suggest that previous studies using the LMDZ4 models underestimated the future increase in SMB in Antarctica by about 30%. Future changes in the Antarctic SMB at low elevations will result from the conflict between higher snow accumulation and runoff. The downscaling model is a powerful tool that can be applied to climate models for a better assessment of a future rise in sea level.