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  • 1.
    Andersson, Lotta
    et al.
    SMHI, Research Department, Hydrology.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Assessment of climate change impact on water resources in the Pungwe river basin2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 138-157Article in journal (Refereed)
  • 2. Brandefelt, J.
    et al.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Naslund, J. -O
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Voelker, A. H. L.
    Wohlfarth, B.
    A coupled climate model simulation of Marine Isotope Stage 3 stadial climate2011In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 7, no 2, p. 649-670Article in journal (Refereed)
  • 3. Brandefelt, Jenny
    et al.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Näslund, Jens-Ove
    Strandberg, Gustav
    Voelker, Antje
    Wohlfarth, Barbara
    The importance of equilibration in glacial climate simulations2010In: Geophysical Research Abstracts, 2010, Vol. 12, article id EGU2010-10736Conference paper (Refereed)
  • 4.
    Bärring, Lars
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Persson, Gunn
    SMHI, Professional Services.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Evaluation of climate extremes in transient runs with the new Rossby Centre regional atmospheric model.2006In: Abstracts of the contributions of the EGU General Assembly 2006, EGU06-A-10110, 2006Conference paper (Other academic)
  • 5. Christensen, Jens Hesselbjerg
    et al.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Giorgi, Filippo
    Lenderink, Geert
    Rummukainen, Markku
    SMHI, Core Services.
    Weight assignment in regional climate models2010In: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 44, no 2-3, p. 179-194Article in journal (Refereed)
    Abstract [en]

    An important new development within the European ENSEMBLES project has been to explore performance-based weighting of regional climate models (RCMs). Until now, although no weighting has been applied in multi-RCM analyses, one could claim that an assumption of 'equal weight' was implicitly adopted. At the same time, different RCMs generate different results, e. g. for various types of extremes, and these results need to be combined when using the full RCM ensemble. The process of constructing, assigning and combining metrics of model performance is not straightforward. Rather, there is a considerable degree of subjectivity both in the choice of metrics and on how these may be combined into weights. We explore the applicability of combining a set of 6 specifically designed RCM performance metrics to produce one aggregated model weight with the purpose of combining climate change information from the range of RCMs used within ENSEMBLES. These metrics capture aspects of model performance in reproducing large-scale circulation patterns, meso-scale signals, daily temperature and precipitation distributions and extremes, trends and the annual cycle. We examine different aggregation procedures that generate different inter-model spreads of weights. The use of model weights is sensitive to the aggregation procedure and shows different sensitivities to the selected metrics. Generally, however, we do not find compelling evidence of an improved description of mean climate states using performance-based weights in comparison to the use of equal weights. We suggest that model weighting adds another level of uncertainty to the generation of ensemble-based climate projections, which should be suitably explored, although our results indicate that this uncertainty remains relatively small for the weighting procedures examined.

  • 6. Christensen, Ole Bossing
    et al.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Zorita, Eduardo
    Projected Change-Atmosphere2015Chapter in book (Other academic)
    Abstract [en]

    This chapter builds on the comprehensive summary of climate change scenarios in the first BACC assessment published in 2008. This chapter first addresses the dynamical downscaling of general circulation model (GCM) results to the regional scale, focussing on results from 13 regional climate model (RCM) simulations in the ENSEMBLES project as this European-scale ensemble simulation is also relevant for the Baltic Sea region and many studies on temperature, precipitation, wind speed and snow amounts have been performed. This chapter then reviews statistical downscaling studies that use large-scale atmospheric variables (predictors) to estimate possible future change in several smaller scale fields (predictands), with the greatest emphasis given to hydrological variables (such as precipitation and run-off). For the Baltic Sea basin, the findings of the statistical downscaling studies are generally in line with studies employing dynamical downscaling.

  • 7. Clausen, Niels-Erik
    et al.
    Pryor, Sara C.
    Larsén, Xiaoli Guo
    Hyvönen, Reijo
    Venäläinen, Ari
    Suvilampi4, Elina
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Barthelmie, Rebecca
    Are we facing increasing extreme winds in the future?2009Conference paper (Other academic)
  • 8. Deque, M
    et al.
    Jones, R G
    Wild, M
    Giorgi, F
    Christensen, J H
    Hassell, D C
    Vidale, P L
    Rockel, B
    Jacob, D
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    de Castro, M
    Kucharski, F
    van den Hurk, B
    Global high resolution versus Limited Area Model climate change projections over Europe: quantifying confidence level from PRUDENCE results2005In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 25, no 6, p. 653-670Article in journal (Refereed)
    Abstract [en]

    Four high resolution atmospheric general circulation models (GCMs) have been integrated with the standard forcings of the PRUDENCE experiment: IPCC-SRES A2 radiative forcing and Hadley Centre sea surface temperature and sea-ice extent. The response over Europe, calculated as the difference between the 2071-2100 and the 1961-1990 means is compared with the same diagnostic obtained with nine Regional Climate Models (RCM) all driven by the Hadley Centre atmospheric GCM. The seasonal mean response for 2m temperature and precipitation is investigated. For temperature, GCMs and RCMs behave similarly, except that GCMs exhibit a larger spread. However, during summer, the spread of the RCMs-in particular in terms of precipitation-is larger than that of the GCMs. This indicates that the European summer climate is strongly controlled by parameterized physics and/or high-resolution processes. The temperature response is larger than the systematic error. The situation is different for precipitation. The model bias is twice as large as the climate response. The confidence in PRUDENCE results comes from the fact that the models have a similar response to the IPCC-SRES A2 forcing, whereas their systematic errors are more spread. In addition, GCM precipitation response is slightly but significantly different from that of the RCMs.

  • 9. Deque, M.
    et al.
    Rowell, D. P.
    Luethi, D.
    Giorgi, F.
    Christensen, J. H.
    Rockel, B.
    Jacob, D.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    de Castro, M.
    van den Hurk, B.
    An intercomparison of regional climate simulations for Europe: assessing uncertainties in model projections2007In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 81, p. 53-70Article in journal (Refereed)
    Abstract [en]

    Ten regional climate models (RCM) have been integrated with the standard forcings of the PRUDENCE experiment: IPCC-SRES A2 radiative forcing and Hadley Centre boundary conditions. The response over Europe, calculated as the difference between the 2071 2100and the 1961-1990 means can be viewed as an expected value about which various uncertainties exist. Uncertainties are measured here by variance in eight sub-European boxes. Four sources of uncertainty can be evaluated with the material provided by the PRUDENCE project. Sampling uncertainty is due to the fact that the model climate is estimated as an average over a finite number of years (30). Model uncertainty is due to the fact that the models use different techniques to discretize the equations and to represent sub-grid effects. Radiative uncertainty is due to the fact that IPCC-SRES A2 is merely one hypothesis. Some RCMs have been run with another scenario of greenhouse gas concentration (IPCC-SRES B2). Boundary uncertainty is due to the fact that the regional models have been run under the constraint of the same global model. Some RCMs have been run with other boundary forcings. The contribution of the different sources varies according to the field, the region and the season, but the role of boundary forcing is generally greater than the role of the RCM, in particular for temperature. Maps of minimum expected 2m temperature and precipitation responses for the IPCC-A2 scenario show that, despite the above mentioned uncertainties, the signal from the PRUDENCE ensemble is significant.

  • 10. Eneroth, K
    et al.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Holmen, K
    A trajectory climatology for Svalbard; investigating how atmospheric flow patterns influence observed tracer concentrations2003In: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 28, no 28-32, p. 1191-1203Article in journal (Refereed)
    Abstract [en]

    A 10-year climatology of long-range atmospheric transport to Ny-(A) over circle lesund, Svalbard (78.9degreesN, 11.9degreesE) is developed using three-dimensional 5-day back-trajectories. We calculate trajectories arriving twice daily at 950, 850 and 750 hPa during 1992-2001, using European Centre for Medium-Range Weather Forecasts (ECMWF) analyzed wind, fields. Cluster analysis is used to classify the trajectories into distinct transport patterns. The clustering procedure is performed on the whole 10-year set of trajectories, to study both year-to-year and mouth-to-mouth variability in the synoptic-scale atmospheric circulation. We identify eight major transport patterns to Ny-(A) over circle lesund, which we find to be consistent with mean-pressure charts of the Arctic region. The distribution of trajectories between these flows is similar for all years during the 10-year period. However, there are seasonal differences in when different clusters are most prevalent. The calculated clusters provide an indication of source regions and transport pathways influencing Svalbard at different times of the year. Such information is valuable for interpreting measured time-series of trace gases and aerosols and could serve as guidance for formulating sampling strategies. We compare the trajectory clusters to CO2 measurements to study to what degree different atmospheric flow patterns influence the variability of the atmospheric CO2. Overall we see a linkage between CO2 concentration and the large-scale circulation. For instance, in connection with transport over Europe and Siberia during winter, high CO2 mixing ratios are observed, whereas trajectories originating from the Atlantic are associated with low CO2 concentrations. However, during some periods and for some individual trajectories we see no conclusive linkage between variability in atmospheric CO2 and transport. This can be due to a combination of the complex structure Of CO2 sources and sinks and its relatively long atmospheric turn-over time. CO2 and Rn-222 mixing ratios are calculated using the three-dimensional transport model MATCH to further illustrate these characteristics of CO2. (C) 2003 Elsevier Ltd. All rights reserved.

  • 11. Gaillard, M. -J
    et al.
    Sugita, S.
    Mazier, F.
    Trondman, A. -K
    Brostrom, A.
    Hickler, T.
    Kaplan, J. O.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Kokfelt, U.
    Kunes, P.
    Lemmen, C.
    Miller, P.
    Olofsson, J.
    Poska, A.
    Rundgren, M.
    Smith, B.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Fyfe, R.
    Nielsen, A. B.
    Alenius, T.
    Balakauskas, L.
    Barnekow, L.
    Birks, H. J. B.
    Bjune, A.
    Bjorkman, L.
    Giesecke, T.
    Hjelle, K.
    Kalnina, L.
    Kangur, M.
    van der Knaap, W. O.
    Koff, T.
    Lageras, P.
    Latalowa, M.
    Leydet, M.
    Lechterbeck, J.
    Lindbladh, M.
    Odgaard, B.
    Peglar, S.
    Segerstrom, U.
    von Stedingk, H.
    Seppa, H.
    Holocene land-cover reconstructions for studies on land cover-climate feedbacks2010In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 6, no 4, p. 483-499Article in journal (Refereed)
    Abstract [en]

    The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past land-cover from pollen data, (3) to present a new project (LANDCLIM: LAND cover - CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS model is demonstrated to provide better estimates of the regional vegetation/land-cover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional- to continental-spatial scale throughout the Holocene. We present maps of REVEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs 'grassland' and 'agricultural land' at five time-windows from 6000 BP to recent time. The LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.

  • 12. Gode, Jenny
    et al.
    Axelsson, Johan
    Eriksson,, Sara
    Holmgren, Kristina
    Hovsenius, Gunnar
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Larsson, Per
    Lundström, Love
    Persson, Gunn
    SMHI, Professional Services.
    Tänkbara konsekvenser för energisektorn av klimatförändringar- Effekter, sårbarhet och anpassning2007Report (Other academic)
  • 13.
    Graham, Phil
    et al.
    SMHI, Professional Services.
    Chen, Deliang
    Bøssing Christensen, Ole
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Krysanova, Valentina
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Radziejewski, Maciej
    Räisänen, Jouni
    Rockel, Burkhardt
    Ruosteenoja, Kimmo
    Projections of Future Anthropogenic Climate Change2008In: Assessment of Climate Change for the Baltic Sea Basin / [ed] The BACC Author Team, Springer, Berlin , 2008, p. 133-219Chapter in book (Other academic)
  • 14.
    Graham, Phil
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Olsson, Jonas
    SMHI, Research Department, Hydrology.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Rosberg, Jörgen
    SMHI, Research Department, Hydrology.
    Hellström, Sara-Sofia
    SMHI, Research Department, Hydrology.
    Berndtsson, Ronny
    Simulating river flow to the Baltic Sea from climate simulations over the past millennium2009In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 14, no 1, p. 173-182Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to reconstruct river flow to the Baltic Sea using data from different periods during the past thousand years. A hydrological model coupled to simulations from climate models was used to estimate river flow. A "millennium" simulation of past climate from the ECHO-G coupled atmosphere-ocean global climate model provided climatological inputs. Results from this global model were downscaled with the RCA3 regional climate model over northern Europe. Temperature and precipitation from the downscaled simulation results were then used in the HBV hydrological model to simulate river flows to the Baltic Sea for the periods 1000-1199 and 1551-1929. These were compared with observations for the period 1921-2002. A general conclusion from this work is that although climate has varied during the past millennium, variability in annual river flow to the Baltic Sea does not appear more pronounced in recent years than during the previous millennium, or vice versa.

  • 15. Hartung, Kerstin
    et al.
    Svensson, Gunilla
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Resolution, physics and atmosphere-ocean interaction - How do they influence climate model representation of Euro-Atlantic atmospheric blocking?2017In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 69, article id 1406252Article in journal (Refereed)
  • 16. Hovsenius, Gunnar
    et al.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Konsekvenser för vindkraften i Sverige av klimatförändringar2007Report (Other academic)
  • 17. Iqbal, W.
    et al.
    Syed, F. S.
    Sajjad, H.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Hannachi, A.
    Mean climate and representation of jet streams in the CORDEX South Asia simulations by the regional climate model RCA42017In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 129, no 1-2, p. 1-19Article in journal (Refereed)
  • 18. Jacob, Daniela
    et al.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Christensen, Ole Bossing
    Christensen, Jens Hesselbjerg
    de Castro, Manuel
    Deque, Michel
    Giorgi, Filippo
    Hagemann, Stefan
    Hirschi, Martin
    Jones, Richard
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Lenderink, Geert
    Rockel, Burkhardt
    Sanchez, Enrique
    Schaer, Christoph
    Seneviratne, Sonia I.
    Somot, Samuel
    van Ulden, Aad
    van den Hurk, Bart
    An inter-comparison of regional climate models for Europe: model performance in present-day climate2007In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 81, p. 31-52Article in journal (Refereed)
    Abstract [en]

    The analysis of possible regional climate changes over Europe as simulated by 10 regional climate models within the context of PRUDENCE requires a careful investigation of possible systematic biases in the models. The purpose of this paper is to identify how the main model systematic biases vary across the different models. Two fundamental aspects of model validation are addressed here: the ability to simulate (1) the long-term (30 or 40 years) mean climate and (2) the inter-annual variability. The analysis concentrates on near-surface air temperature and precipitation over land and focuses mainly on winter and summer. In general, there is a warm bias with respect to the CRU data set in these extreme seasons and a tendency to cold biases in the transition seasons. In winter the typical spread (standard deviation) between the models is 1 K. During summer there is generally a better agreement between observed and simulated values of inter-annual variability although there is a relatively clear signal that the modeled temperature variability is larger than suggested by observations, while precipitation variability is closer to observations. The areas with warm (cold) bias in winter generally exhibit wet (dry) biases, whereas the relationship is the reverse during summer (though much less clear, coupling warm (cold) biases with dry (wet) ones). When comparing the RCMs with their driving GCM, they generally reproduce the large-scale circulation of the GCM though in some cases there are substantial differences between regional biases in surface temperature and precipitation.

  • 19. Kendon, Elizabeth J.
    et al.
    Jones, Richard G.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Murphy, James M.
    Using and Designing GCM-RCM Ensemble Regional Climate Projections2010In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 23, no 24, p. 6485-6503Article in journal (Refereed)
    Abstract [en]

    Multimodel ensembles, whereby different global climate models (GCMs) and regional climate models (RCMs) are combined, have been widely used to explore uncertainties in regional climate projections. In this study, the extent to which information can be enhanced from sparsely filled GCM RCM ensemble matrices and the way in which simulations should be prioritized to sample uncertainties most effectively are examined. A simple scaling technique, whereby the local climate response in an RCM is predicted from the large-scale change in the GCM, is found to often show skill in estimating local changes for missing GCM RCM combinations. In particular, scaling shows skill for precipitation indices (including mean, variance, and extremes) across Europe in winter and mean and extreme temperature in summer and winter, except for hot extremes over central/northern Europe in summer. However, internal variability significantly impacts the ability to determine scaling skill for precipitation indices, with a three-member ensemble found to be insufficient for identifying robust local scaling relationships in many cases. This study suggests that, given limited computer resources, ensembles should be designed to prioritize the sampling of GCM uncertainty, using a reduced set of RCMs. Exceptions are found over the Alps and northeastern Europe in winter and central Europe in summer, where sampling multiple RCMs may be equally or more important for capturing uncertainty in local temperature or precipitation change. This reflects the significant role of local processes in these regions. Also, to determine the ensemble strategy in some cases, notably precipitation extremes in summer, better sampling of internal variability is needed.

  • 20.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Daily variability in temperature and precipitation: Recent and future changes over Europe2005In: EXTENDED ABSTRACTS of a WMO/WCRP-sponsored REGIONAL-SCALE CLIMATE MODELLING WORKSHOP: HIGH-RESOLUTION CLIMATE MODELLING: ASSESSMENT, ADDED VALUE AND APPLICATIONS / [ed] Lars Bärring & René Laprise, Department of Physical Geography & Ecosystems Analysis Lund University, Sweden , 2005, Vol. 5, p. 72-73Conference paper (Other academic)
  • 21.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Evaluating regional climate model simulations of daily maximum and minimum temperatures in the ENSEMBLES project2008In: Abstracts of the contributions of the EGU General Assembly 2008, 2008, Vol. 10, article id EGU2008-A-02262Conference paper (Other academic)
  • 22.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Present-Day and Future Precipitation in the Baltic Region as Simulated in Regional Climate Models2004In: Fourth Study Conference on BALTEX: Conference Proceedings / [ed] Hans-Jörg Isemer, Risø National Laboratory Technical University of Denmark GKSS Forschungszentrum Geesthacht GmbH , 2004, p. 170-171Conference paper (Other academic)
  • 23.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Recent and future signatures of climate change in Europe2004In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 33, no 4-5, p. 193-198Article in journal (Refereed)
    Abstract [en]

    A set of six regional climate model experiments is investigated for future changes in daily temperature and precipitation in Europe. Changes in the probability distributions for these variables are studied. It is found that the asymmetry of these distributions change differently depending on location and season. Large summertime changes in extremely high temperatures in central, eastern and southern Europe are followed by higher than average temperature increases on warm days in general. Likewise, temperatures on cold days increase much more than the average temperature increase during winter in eastern and northern Europe. A comparison with historical data on wintertime temperature shows that the model simulated and observed daily variability are similar. In particular, the much stronger increase in temperatures on cold days, compared to the average temperature increase as observed in warm compared to cold historical periods, is simulated also by the model. The contribution from heavy precipitation events is simulated to increase over most parts of Europe in all seasons.

  • 24.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Abrahamsson, Reino
    Naturvårdsverket.
    Boberg, Pelle
    Naturvårdsverket.
    Jernbäcker, Eva
    Naturvårdsverket.
    Karlberg, Marie
    Energimyndigheten.
    Morel, Julien
    Energimyndigheten.
    Uppdatering av det klimatvetenskapliga kunskapsläget2014Report (Other academic)
    Abstract [sv]

    Det klimatvetenskapliga kunskapsläget har förstärkts ytterligare under senare år. IPCC:s utvärderingsrapporter utgör de mest omfattande synteserna som finns på området. Huvudbudskapen i den senaste utvärderingsrapporten (AR5) är i allt väsentligt i linje med föregående rapport, även om ny kunskap har tillkommit och tidigare kunskap fördjupats.Uppvärmningen av klimatsystemet har fortsatt och människans påverkan är tydligSäkerheten i slutsatsen att människan påverkar klimatet har successivt stärkts i varje ny utvärderingsrapport från IPCC. Till de observerade förändringarna i klimatet hör att den lägre atmosfären och haven blivit varmare, nederbördsmönster ändrats, snötäckets utbredning på norra halvklotet liksom utbredningen av Arktis havsis har minskat. Som följd av uppvärmningen minskar också istäcket på Grönland och Antarktis samtidigt som många glaciärer smälter vilket bidrar till den stigande havsnivån. De ökade halterna av växthusgaser i atmosfären, främst koldioxid till följd av människans utsläpp, påverkar jordens strålningsbalans och är den främsta orsaken till den snabba uppvärmningen.Vi står inför fortsatt kraftig klimatförändring med allvarliga konsekvenserHur stor den framtida klimatförändringen blir beror på graden av ändrad strålningsbalans samt på klimatsystemets respons. Av de klimatscenarier som presenteras i AR5 är det bara i scenariot med minst klimatpåverkan som ökningen av den globala medel-temperaturen sannolikt inte kommer att överstiga 2°C jämfört med förindustriella nivåer. I ett scenario med nuvarande politik kan temperaturöverskridandet bli över 4°C och havsytans medelnivå höjas med uppemot en meter, eller möjligen mer, till år 2100. Generellt förväntas nederbörden öka där det redan regnar mycket och minska där det är torrt. Förekomsten av extrema väderhändelser förväntas också öka. Följdeffekterna inkluderar mer översvämningar och torka, och därigenom större risk för spridning av sjukdomar, brist på rent vatten och skördebortfall.Klimatförändringar drabbar redan utsatta värst, men Sverige påverkas också negativtFramtida klimatförändringar väntas innebära en rad negativa effekter för människor, samhällen och ekosystem. Dessa effekter blir mer kännbara vid högre grad av klimatpåverkan. IPCC slår fast att ytterligare uppvärmning ger en ökad sannolikhet för allvarliga, genomträngande och bestående effekter. Detta rör t.ex. hotade ekosystem i stora delar av världen där många arter kan komma att utrotas, kustnära samhällen som hotas av havsnivåhöjning och negativ påverkan på livsmedelsförsörjning. Även sekundära effekter som försvårande av fattigdomsbekämpning och ökad risk för skärpta konflikter i redan utsatta delar av världen pekas på som risker för samhället.Sveriges klimat har blivit varmare och mer nederbördsrikt. Fortsatta förändringar är att vänta och även om den globala medeltemperaturökningen begränsas till under 2 °C väntas kraftiga förändringar som kan komma att påverka samhället och naturmiljön. Skyfall och kraftiga regn förväntas öka i intensitet vilket kan ge ökade problem med översvämningar. Översvämningar kan också komma att drabba låglänta kusttrakter i södra Sverige p.g.a. stigande havsnivåer. Uppvärmningen väntas få konsekvenser för jord- och skogsbruk och även för naturliga ekosystem, inte minst i fjällkedjan där trädgränsen förväntas flytta högre upp i terrängen.Om vi agerar kraftfullt kan den globala temperaturökningen fortfarande begränsas till under 2 °CVärldens utsläpp fortsätter öka snabbt. Utsläppen av koldioxid mellan 1970 och 2010 överskred den sammanlagda mängden som släpptes ut före 1970. Den kraftiga ökningen av utsläppen mellan 2000 och 2010 har främst skett i tillväxtekonomier. Utsläppen bedöms fortsätta öka även i framtiden med dagens beslutade politik och styrmedel.För att "sannolikt" (med mer än 66 procents sannolikhet) begränsa temperaturökningen till under 2 °C år 2100 behöver de globala utsläppen nå sin kulmen inom en snar framtid, minska med 40 till 70 procent till år 2050 och till nära noll eller bli negativa år 2100. En så stor utsläppsreduktion kräver omfattande omställningar världen över i såväl industrialiserade som i snabbt växande ekonomier. Internationellt samarbete och verktyg för att främja utsläppsminskning är därför nödvändiga. För att begränsa effekterna och sårbarheten för de klimatförändringar som uppstår måste åtgärderna för utsläpps-minskningar kompletteras med klimatanpassningsåtgärder.Åtgärder för utsläppsminskning måste sättas in snart och kommer att krävas under mycket lång tidPå kort sikt behöver inlåsningar i koldioxidintensiv och energikrävande teknik och samhällsbyggnad undvikas genom att bygga hållbart från början. En sådan inriktning gör det också enklare att utveckla mer hållbara beteendemönster. Inriktningen är särskilt viktigt i de delar av världen där en stor mängd städer och energianläggningar nu håller på att byggas och expandera men också när tidigt industrialiserade länder nu genomför åter-investeringar i den befintliga bebyggelsen och infrastrukturen.Eftersom energieffektivisering minskar behovet av att tillföra ytterligare energi i systemet visar IPCC:s scenariomodelleringar att omfattande investeringar behöver göras i energi-effektiviserande åtgärder i perioden innan 2030.På lång sikt behöver energi- och resursanvändningen bli mycket mer effektiv än i dag, energitillförseln behöver nå nollutsläpp eller till och med negativa utsläpp och upptaget av koldioxid i skog och mark behöver öka. Ökad tillgång på bioenergi som producerats på ett hållbart sätt är viktigt för att få ner kostnaderna för omställningen. Försenas utsläpps-minskningarna ökar risken för allvarliga klimatförändringar och kostnaderna för klimat-politiken betydligt. IPCC-rapporten visar att ju längre världens länder väntar, desto mer behöver världen förlita sig på en omfattande användning av osäkra tekniker såsom bio-baserade energianläggningar med koldioxidfångning och lagring (bio-CCS) för att kunna åstadkomma negativa utsläpp (upptag av koldioxid från atmosfären) till år 2100.Klimatåtgärder som en del av hållbar utvecklingKlimatåtgärderna kan i många fall leda till positiva synergier med andra samhällsmål t.ex. när åtgärderna även innebär att vi hushåller med energi och vatten, att utsläppen av luft-föroreningar minskar, att det utvecklas ett hållbart jord- och skogsbruk, att energi-fattigdom minskar samt genom att ekosystemtjänster upprätthålls. Samtidigt kan klimat-åtgärder även medföra risker för negativa sidoeffekter, t.ex. om användningen av bioenergi utvecklas i konflikt med livsmedelsproduktion och biodiversitet. IPCC-rapporten betonar därför vikten av att främja de åtgärder som skapar synergier med andra samhällsmål, inklusive anpassning till klimatförändringarna.

  • 25.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Boberg, Fredrik
    Castro, Manuel
    Christensen, Jens Hesselbjerg
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Sanchez, Enrique
    Daily and monthly temperature and precipitation statistics as performance indicators for regional climate models2010In: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 44, no 2-3, p. 135-150Article in journal (Refereed)
    Abstract [en]

    We evaluated daily and monthly statistics of maximum and minimum temperatures and precipitation in an ensemble of 16 regional climate models (RCMs) forced by boundary conditions from reanalysis data for 1961-1990. A high-resolution gridded observational data set for land areas in Europe was used. Skill scores were calculated based on the match of simulated and observed empirical probability density functions. The evaluation for different variables, seasons and regions showed that some models were better/worse than others in an overall sense. It also showed that no model that was best/worst in all variables, seasons or regions. Biases in daily precipitation were most pronounced in the wettest part of the probability distribution where the RCMs tended to overestimate precipitation compared to observations. We also applied the skill scores as weights used to calculate weighted ensemble means of the variables. We found that weighted ensemble means were slightly better in comparison to observations than corresponding unweighted ensemble means for most seasons, regions and variables. A number of sensitivity tests showed that the weights were highly sensitive to the choice of skill score metric and data sets involved in the comparison.

  • 26.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Brandefelt, J.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Smith, B
    Wohlfart, B
    Näslund, J-O
    Extreme climate conditions in Sweden in a 100,000 year perspective as simulated by global and regional climate models2009Conference paper (Other academic)
  • 27.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Brandefelt, J
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Smith, B
    Wohlfart, B
    Näslund, J-O
    Global and regional climate model simulations of extreme climate conditions in Sweden in a 100,000 year perspective2008In: Abstracts of the contributions of the EGU General Assembly 2008., 2008, Vol. 10, article id EGU2008-A-02249Conference paper (Other academic)
  • 28.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Brandefelt, Jenny
    Naslund, Jens-Ove
    Smith, Ben
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Voelker, Antje H. L.
    Wohlfarth, Barbara
    Simulated climate conditions in Europe during the Marine Isotope Stage 3 stadial2010In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 39, no 2, p. 436-456Article in journal (Refereed)
    Abstract [en]

    State-of-the-art climate models were used to simulate climate conditions in Europe during Greenland Stadial (GS) 12 at 44 ka BP. The models employed for these simulations were: (i) a fully coupled atmosphere-ocean global climate model (AOGCM), and (ii) a regional atmospheric climate model (RCM) to dynamically downscale results from the global model for a more detailed investigation of European climate conditions. The vegetation was simulated off-line by a dynamic vegetation model forced by the climate from the RCM. The resulting vegetation was then compared with the a priori vegetation used in the first simulation. In a subsequent step, the RCM was rerun to yield a new climate more consistent with the simulated vegetation. Forcing conditions included orbital forcing, land-sea distribution, ice-sheet configuration, and atmospheric greenhouse gas concentrations representative for 44 ka BP. The results show a cold climate on the global scale, with global annual mean surface temperatures 5 degrees C colder than the modern climate. This is still significantly warmer than temperatures derived from the same model system for the Last Glacial Maximum (LGM). Regional, northern European climate is much colder than today, but still significantly warmer than during the LGM. Comparisons between the simulated climate and proxy-based sea-surface temperature reconstructions show that the results are in broad agreement, albeit with a possible cold bias in parts of the North Atlantic in summer. Given a prescribed restricted Marine Isotope Stage 3 ice-sheet configuration, with large ice-free regions in Sweden and Finland, the AOGCM and RCM model simulations produce a cold and dry climate in line with the restricted ice-sheet configuration during GS 12. The simulated temperature climate, with prescribed ice-free conditions in south-central Fennoscandia, is favourable for the development of permafrost, but does not allow local ice-sheet formation as all snow melts during summer.

  • 29.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Evaluating the method of pattern-scaling in time2006Conference paper (Other academic)
  • 30.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Gollvik, Stefan
    Meterologi.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    A 140-year simulation of European climate with the new version of the Rossby Centre regional atmospheric climate model (RCA3)2005Report (Other academic)
    Abstract [en]

    This report presents the latest version of the Rossby Centre regional atmospheric model, RCA3, with focus on model improvements since the earlier version, RCA2. The main changes in RCA3 relate to the treatment of land surface processes. Apart from the changes in land surface parameterizations several changes in the calculation of radiation, clouds, condensate and precipitation have been made. The new parameterizations hold a more realistic description of the climate system.Simulated present day climate is evaluated compared to observations. The new model version show equally good, or better, correspondence to observational climatologies as RCA2, when forced by perfect boundary conditions. Seasonal mean temperature errors are generally within ±1oC except during winter in north-western Russia where a larger positive bias is identified. Both the diurnal temperature range and the annual temperature range are found to be underestimated in the model. Precipitation biases are generally smaller than in the corresponding reanalysis data used as boundary conditions, showing the benefit of a higher horizontal resolution.The model is used for the regionalization of two transient global climate change projections for the time period 1961- 2100. The radiative forcing of the climate system is based on observed concentrations of greenhouse gases until 1990 and on the IPCC SRES B2 and A2 emissions scenarios for the remaining time period. Long-term averages as well as measures of the variability around these averages are presented for a number of variables including precipitation and near-surface temperature. It is shown that the changes in variability sometimes differ from the changes in averages. For instance, in north-eastern Europe, the mean increase in wintertime temperatures is followed by an even stronger reduction in the number of very cold days in winter. This kind of performance of the climate system implies that methods of inferring data from climate change projections to other periods than those actually simulated have to be used with care, at least when it comes to variables that are expected to change in a non-linear way. Further, these new regional climate change projections address the whole 21st century.

  • 31.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Jacob, Daniela
    Jones, Richard
    Lenderink, Geert
    Schaer, Christoph
    Modelling daily temperature extremes: recent climate and future changes over Europe2007In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 81, p. 249-265Article in journal (Refereed)
    Abstract [en]

    Probability distributions of daily maximum and minimum temperatures in a suite of ten RCMs are investigated for (1) biases compared to observations in the present day climate and (2) climate change signals compared to the simulated present day climate. The simulated inter-model differences and climate changes are also compared to the observed natural variability as reflected in some very long instrumental records. All models have been forced with driving conditions from the same global model and run for both a control period and a future scenario period following the A2 emission scenario from IPCC. We find that the bias in the fifth percentile of daily minimum temperatures in winter and at the 95th percentile of daily maximum temperature during summer is smaller than 3 (+/- 5 degrees C) when averaged over most (all) European sub-regions. The simulated changes in extreme temperatures both in summer and winter are larger than changes in the median for large areas. Differences between models are larger for the extremes than for mean temperatures. A comparison with historical data shows that the spread in model predicted changes in extreme temperatures is larger than the natural variability during the last centuries.

  • 32.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Atmospheric response to different sea surface temperatures in the Baltic Sea: coupled versus uncoupled regional climate model experiments2005In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 36, no 4-5, p. 397-409Article in journal (Refereed)
    Abstract [en]

    A climate change experiment with a fully coupled high resolution regional atmosphere-ocean model for the Baltic Sea is compared to an experiment with a stand-alone regional atmospheric model. Both experiments simulate 30-yr periods with boundary data from the same global climate model system. This particular global model system simulates very high sea surface temperatures during summer for the Baltic Sea at the end of this century under the investigated emission scenario. We show that the sea surface temperatures are less warm in the coupled regional model compared to the global model system and that this difference is dependent on the atmospheric circulation. In summers with a high NAO index and thereby relatively strong westerly flow over the North Atlantic the differences between the two models are small, while in summers with a weaker, more northerly flow over the Baltic Sea the differences are very large. The higher sea surface temperatures in the uncoupled experiment lead to an intensified hydrological cycle over the Baltic Sea, with more than 30% additional precipitation in summer taken as an average over the full 30-yr period and over the entire Baltic Sea. The differences are mostly local, over the sea, but there are differences in surrounding land areas.

  • 33.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Drews, M.
    Christensen, J. H.
    Haugen, J.E.
    Haakenstad, H.
    Shkolnik, I.
    An ensemble of regional climate change scenarios for the nordic countries.2010Conference paper (Other academic)
  • 34.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Giorgi, Filippo
    Regional Climate Model evaluation and weighting Introduction2010In: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 44, no 2-3, p. 117-119Article in journal (Other academic)
    Abstract [en]

    An ensemble of regional climate models downscaling reanalysis data has been evaluated against observations for the time period 1961-2000. Various aspects of model performance including both their representation of large-scale features and their ability to add value on smaller spatial scales have been considered. A set of metrics has been derived and combined into a performance-based weigthing system that is used in the production of probabilistic climate change projections. Strengths and weaknesses of weighting techniques for RCM ensembles are discussed.

  • 35.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Holmen, K
    Eneroth, K
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    Summertime Siberian CO2 simulations with the regional transport model MATCH: a feasibility study of carbon uptake calculations from EUROSIB data2002In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 54, no 5, p. 834-849Article in journal (Refereed)
    Abstract [en]

    Biogenic surface fluxes Of CO2 over Europe and Siberia are implemented in the regional tracer transport model MATCH. A systematic comparison between simulated and observed CO2 fluxes and mixing ratios is performed for two observational sites in Russia taking into account both surface observations and vertical profiles of meteorological parameters and CO2 in the lowest 3 km from the summer months in 1998. We find that the model is able to represent meteorological parameters as temperature, humidity and planetary boundary layer height consistent with measurements. Further, it is found that the simulated surface CO2 fluxes capture a large part of the observed variability on a diurnal time scale. On a synoptic time scale the agreement between observations and simulation is poorer which leads to a disagreement between time series of observed and simulated CO2 mixing ratios. However, the model is able to realistically simulate the vertical gradient in CO2 in the lowest few kilometres. The vertical variability is studied by means of trajectory analysis together with results from the MATCH model. This analysis clearly illustrates some problems in deducing CO2 fluxes from CO2 mixing ratios measured in single vertical profiles. Studies of the regional variability Of CO2 in the model domain show that there exists no ideal vertical level for detecting the terrestrial signal Of CO2 in the free troposphere. The strongest terrestrial signal is found in the boundary layer above the lowest few hundred metres. Nevertheless, this terrestrial signal is small, and during the simulated period it is not possible to detect relative variations in the surface fluxes smaller than 20%. We conclude that a regional flux cannot be determined from single ground stations or a few vertical profiles, mainly due to synoptic scale variability in transport and in CO2 surface fluxes.

  • 36.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Lind, Petter
    Changes in the Water and Energy Budgets in the BALTEX Area in Future Warmer Climates as Simulated in a Regional Climate Model2007Conference paper (Other academic)
  • 37.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Lind, Petter
    SMHI, Research Department, Climate research - Rossby Centre.
    Changes in the water budget in the Baltic Sea drainage basin in future warmer climates as simulated by the regional climate model RCA32009In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 14, no 1, p. 114-124Article in journal (Refereed)
    Abstract [en]

    In this study we investigate three different regional climate change scenarios with respect to changes in the water budget over the Baltic Sea drainage basin. The scenarios are transient climate change scenarios in which the regional climate model RCA3 has been used to downscale results from two general circulation models, with three different emissions scenarios, for the years 1961-2100. First we show that the control climate in the late 20th century is too wet as compared with observations. This wet bias in the simulations is partly attributable to biases in the forcing global models but is also amplified in the regional climate model. The future climate change signal shows a gradually warmer and wetter climate during the 21st century with increased moisture transport into the region via the atmosphere. This leads to an intensification of the hydrological cycle with more precipitation and evaporation. The net precipitation increases in all scenarios in the entire region. The changes are of the order 15%-20% for annual and areal mean fluxes.

  • 38.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Changes in seasonal mean European temperature and precipitation climate from an ensemble of transient RCM simulations driven by several AOGCMs2009Conference paper (Other academic)
  • 39.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Climate change in the Baltic Sea area in an ensemble of regional climate model simulations2010Conference paper (Other academic)
  • 40.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    An ensemble of regional climate change simulations2009In: / [ed] Rockel, B., Bärring, L and Reckermann, M., 2009, p. 134-135Conference paper (Other academic)
  • 41.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    21st century changes in the European climate: uncertainties derived from an ensemble of regional climate model simulations2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 24-40Article in journal (Refereed)
  • 42.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    21st century changes in the Nordic climate: 8ncertainties derived from an ensemble of regional climate model simulations2010Conference paper (Other academic)
  • 43.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Seasonal mean temperature, precipitation and wind speed in Europe from an ensemble of 16 transient RCM simulations for 1961-21002010In: Geophysical Research Abstracts, 2010, Vol. 12, article id EGU2010-10229Conference paper (Refereed)
  • 44.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Christensen, Ole Bossing
    Jacob, Daniela
    Keuler, Klaus
    Lenderink, Geert
    van Meijgaard, Erik
    Schar, Christoph
    Somot, Samuel
    Sorland, Silje Lund
    Teichmann, Claas
    Vautard, Robert
    European climate change at global mean temperature increases of 1.5 and 2 degrees C above pre-industrial conditions as simulated by the EURO-CORDEX regional climate models2018In: Earth System Dynamics, ISSN 2190-4979, E-ISSN 2190-4987, Vol. 9, no 2, p. 459-478Article in journal (Refereed)
  • 45.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Ruosteenoja, Kimmo
    Present-day and future precipitation in the Baltic Sea region as simulated in a suite of regional climate models2007In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 81, p. 281-291Article in journal (Refereed)
    Abstract [en]

    Here we investigate simulated changes in the precipitation climate over the Baltic Sea and surrounding land areas for the period 2071-2100 as compared to 1961-1990. We analyze precipitation in 10 regional climate models taking part in the European PRUDENCE project. Forced by the same global driving climate model, the mean of the regional climate model simulations captures the observed climatological precipitation over the Baltic Sea runoff land area to within 15% in each month, while single regional models have errors up to 25%. In the future climate, the precipitation is projected to increase in the Baltic Sea area, especially during winter. During summer increased precipitation in the north is contrasted with a decrease in the south of this region. Over the Baltic Sea itself the future change in the seasonal cycle of precipitation is markedly different in the regional climate model simulations. We show that the sea surface temperatures have a profound impact on the simulated hydrological cycle over the Baltic Sea. The driving global climate model used in the common experiment projects a very strong regional increase in summertime sea surface temperature, leading to a significant increase in precipitation. In addition to the common experiment some regional models have been forced by either a different set of Baltic Sea surface temperatures, lateral boundary conditions from another global climate model, a different emission scenario, or different initial conditions. We make use of the large number of experiments in the PRUDENCE project, providing an ensemble consisting of more than 25 realizations of climate change, to illustrate sources of uncertainties in climate change projections.

  • 46.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Thejll, Peter
    Rummukainen, Markku
    SMHI, Core Services.
    Christensen, Jens H.
    Boberg, Fredrik
    Christensen, Ole B.
    Maule, Cathrine Fox
    Emerging regional climate change signals for Europe under varying large-scale circulation conditions2013In: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 56, no 2, p. 103-119Article in journal (Refereed)
    Abstract [en]

    A large ensemble of regional climate model projections was investigated regarding if and when they show an emergence of significant climate change signals in seasonal temperature and precipitation within Europe. The influence of the North Atlantic Oscillation (NAO), as simulated in the projections, was investigated. In most parts of Europe, the projections indicate robust emergence of temperature change in the first 2 decades of the 21st century, typically earlier for summer than for winter. For precipitation changes, signals generally emerge much later than for temperature. For Europe as a whole, the precipitation signals tend to emerge some 40 to 60 yr later than the temperature signals. In some sub-regions, robust signals for precipitation are not found within the studied period, i.e. until 2100. Some sub-regions, notably the Mediterranean area and Scandinavia, show different behaviour in some aspects compared to the ensemble-based results as a whole. NAO has some influence on the temperature change signals, which emerge earlier in winter for some models and regions if NAO is accounted for. For summer temperatures, the influence of NAO is less evident. Similarly, for precipitation, accounting for NAO leads to an earlier emergence in some regions and models. Here, we find an impact for both summer and winter.

  • 47. Lind, Petter
    et al.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Investigation of the Water and Energy Budgets in the BALTEX Area, as Simulated in a Regional Climate Model2007Conference paper (Other academic)
  • 48.
    Lind, Petter
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Temperature and precipitation changes in Sweden; a wide range of model-based projections for the 21st century2008Report (Other academic)
    Abstract [en]

    In this report we analyze the climate change signal for Sweden in scenarios for the 21st century in a large number of coupled atmosphere-ocean general circulation models (AOGCMs), used in the fourth assessment report by the Intergovernmental Panel on Climate Change (IPCC). We focus on near-surface temperature and precipitation. The analysis includes six emission scenarios as well as multi-member runs with the AOGCMs. At the Rossby Centre, SMHI, regional climate models have been run under different emission scenarios and driven by a few AOGCMs. The results of those runs have been used as a basis in climate change, impact and adaptation assessments. Here, we evaluate results from these regional climate model runs in relation to the climate change signal of the IPCC AOGCMs. First, simulated conditions for the recent past (1961-1990) are evaluated. Generally, most AOGCMs tend to have a cold bias for Sweden, especially in winter that can be as large as 10°C. Also, the coarse resolution of the AOGCMs leads to biases in simulated precipitation, both in averages, extremes and often also in the phase of the seasonal cycle. Generally, AOGCMs overestimate precipitation in winter; biases reach 30-40% or even more. In summer, some AOGCMs overestimate precipitation while others underestimate it. Projected responses depend on season and geographical region. Largest signals are seen in winter and in northern Sweden, where the mean simulated temperature increase among the AOGCMs (and across the emissions scenarios B1, A1B and A2) is nearly 6°C by the end of the century, and precipitation increases by around 25%. In southern Sweden, corresponding values are around +4°C and +11%. In summer, the temperature increase is more moderate, which is also the case for precipitation. The regional climate signals are usually within the ranges given by the AOGCM runs, however, the regional models tends to show larger increases in winter, and smaller increases in summertime precipitation.

  • 49.
    Lind, Petter
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Water budget in the Baltic Sea drainage basin: Evaluation of simulated fluxes in a regional climate model2009In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 14, no 1, p. 56-67Article in journal (Refereed)
    Abstract [en]

    We investigated the Rossby Centre regional climate model, RCA3, and its ability to reproduce the water budget of the Baltic Sea drainage basin during the period from 1979 to 2002. The model was forced on its lateral boundaries with European Centre for Medium-Range Weather Forecasts Re-Analysis data, ERA40. Simulated long-term means and inter-annual variability were compared with observational records and model-derived data. The basin-wide water fluxes were broadly captured by the model, and annual mean net precipitation over land agreed well (i.e., within 5%) with observed total discharge to the Baltic Sea. Long-term annual means of precipitation were around 20% higher in RCA3 compared with reference data, the differences being in most months statistically significant at the 5% level. On the other hand, differences between the reference datasets were evident and in most months also statistically significant. The inclusion of a high-resolution dataset showed a close agreement compared with RCA3; differences were less than 5% in the long-term annual mean. Therefore, more high-resolution observational datasets, especially for evaporation and runoff, are required to refine the water budget and compare water fluxes on sub-regional and local scales.

  • 50.
    Lind, Petter
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Lindstedt, David
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Spatial and Temporal Characteristics of Summer Precipitation over Central Europe in a Suite of High-Resolution Climate Models2016In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 29, no 10, p. 3501-3518Article in journal (Refereed)
12 1 - 50 of 99
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