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  • 1. Abbott, Peter M.
    et al.
    Davies, Siwan M.
    Steffensen, Jorgen Peder
    Pearce, Nicholas J. G.
    Bigler, Matthias
    Johnsen, Sigfus J.
    Seierstad, Inger K.
    Svensson, Anders
    Wastegård, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    A detailed framework of Marine Isotope Stages 4 and 5 volcanic events recorded in two Greenland ice-cores2012Ingår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 36, s. 59-77Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval: the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grimsvotn, Grimsvotn-Kverkfjoll and either Reykjanes or Veidivotn-Bardarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICCO5 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences.

  • 2.
    Acosta Navarro, Juan Camilo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Anthropogenic influence on climate through changes in aerosol emissions from air pollution and land use change2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Particulate matter suspended in air (i.e. aerosol particles) exerts a substantial influence on the climate of our planet and is responsible for causing severe public health problems in many regions across the globe. Human activities have altered the natural and anthropogenic emissions of aerosol particles through direct emissions or indirectly by modifying natural sources. The climate effects of the latter have been largely overlooked. Humans have dramatically altered the land surface of the planet causing changes in natural aerosol emissions from vegetated areas. Regulation on anthropogenic and natural aerosol emissions have the potential to affect the climate on regional to global scales. Furthermore, the regional climate effects of aerosol particles could potentially be very different than the ones caused by other climate forcers (e.g. well mixed greenhouse gases). The main objective of this work was to investigate the climatic effects of land use and air pollution via aerosol changes.

    Using numerical model simulations it was found that land use changes in the past millennium have likely caused a positive radiative forcing via aerosol climate interactions. The forcing is an order of magnitude smaller and has an opposite sign than the radiative forcing caused by direct aerosol emissions changes from other human activities. The results also indicate that future reductions of fossil fuel aerosols via air quality regulations may lead to an additional warming of the planet by mid-21st century and could also cause an important Arctic amplification of the warming. In addition, the mean position of the intertropical convergence zone and the Asian monsoon appear to be sensitive to aerosol emission reductions from air quality regulations. For these reasons, climate mitigation policies should take into consideration aerosol air pollution, which has not received sufficient attention in the past.

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    Anthropogenic influence on climate through changes in aerosol emissions from air pollution and land use change
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  • 3.
    Acosta Navarro, Juan Camilo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Historical anthropogenic radiative forcing of changes in biogenic secondary organic aerosol2015Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Human activities have lead to changes in the energy balance of the Earth and the global climate. Changes in atmospheric aerosols are the second largest contributor to climate change after greenhouse gases since 1750 A.D. Land-use practices and other environmental drivers have caused changes in the emission of biogenic volatile organic compounds (BVOCs) and secondary organic aerosol (SOA) well before 1750 A.D, possibly causing climate effects through aerosol-radiation and aerosol-cloud interactions. Two numerical emission models LPJ-GUESS and MEGAN were used to quantify the changes in aerosol forming BVOC emissions in the past millennium. A chemical transport model of the atmosphere (GEOS-Chem-TOMAS) was driven with those BVOC emissions to quantify the effects on radiation caused by millennial changes in SOA.

    The specific objectives of this licentiate thesis are: 1) to understand what drove the changes in aerosol-forming BVOC emissions (i.e. isoprene, monoterpenes and sesquiterpenes) and to quantify these changes; 2) to calculate for the first time the combined historical aerosol direct and aerosol-cloud albedo effects on radiation from changing BVOC emissions through SOA formation; 3) to investigate how important the biological climate feedback associated to BVOC emissions and SOA formation is from a global climate perspective.

    We find that global isoprene emissions decreased after 1800 A.D. by about 12% - 15%. This decrease was dominated by losses of natural vegetation, whereas monoterpene and sesquiterpene emissions increased by about 2% - 10%, driven mostly by rising surface air temperatures. From 1000 A.D. to 1800 A.D, isoprene, monoterpene and sesquiterpene emissions decline by 3% - 8% driven by both, natural vegetation losses, and the moderate global cooling between the medieval climate anomaly and the little ice age. The millennial reduction in BVOC emissions lead to a 0.5% to 2% reduction in climatically relevant aerosol particles (> 80 nm) and cause a direct radiative forcing between +0.02 W/m² and +0.07 W/m², and an indirect radiative forcing between -0.02 W/m² and +0.02 W/m². The suggested biological climate feedback seems to be too small to have observable consequences on the global climate in the recent past.

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  • 4. Adachi, Kouji
    et al.
    Tobo, Yutaka
    Oshima, Naga
    Yoshida, Atsushi
    Ohata, Sho
    Krejci, Radovan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap. Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Massling, Andreas
    Skov, Henrik
    Koike, Makoto
    Composition and mixing state of individual aerosol particles from northeast Greenland and Svalbard in the Arctic during spring 20182023Ingår i: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 314, artikel-id 120083Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arctic region is warming about four times faster than the rest of the globe, and thus it is important to understand the processes driving climate change in this region. Aerosols are a significant component of the Arctic climate system as they form ice crystals and liquid droplets that control the dynamics of clouds and also directly interact with solar radiation, depending on the compositions and mixing states of individual particles. Here, we report on the characteristics of submicron-sized aerosol particles using transmission electron microscopy obtained at two high Arctic sites, northeast Greenland (Villum Research Station) and Svalbard (Zeppelin Observatory), during spring 2018. The results showed that a dominant compound in the submicron-sized spring aerosols was sulfate, followed by sea salt particles. Both model simulations and observations at the Zeppelin Observatory showed that sea salt particles became more prevalent when low-pressure systems passed by the station. Model simulations indicate that both sampling sites were affected by diffused and diluted long-range transport of anthropogenic aerosols from lower latitudes with negligible influences of biomass burning emissions during the observation period. Overall, the composition of measured aerosol particles from the two Arctic sites was generally similar and showed no apparent variation except for the sea salt fractions. This study shows a general picture of high Arctic aerosol particles influenced by marine sources and diffused long-range transport of anthropogenic sources during the Arctic spring period. These results will contribute to a better knowledge of the aerosol composition and mixing state during the Arctic spring, which helps to understand the contributions of aerosols to the Arctic climate.

  • 5.
    Ahmed, Moinuddin
    et al.
    Fed Urdu Univ Arts Sci & Technol, Dept Bot, Karachi 75300, Pakistan.
    Krusic, Paul J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Charpentier Ljungqvist, Fredrik
    Stockholms universitet, Humanistiska fakulteten, Historiska institutionen.
    Zorita, Eduardo
    PAGES 2k Consortium,
    Continental-scale temperature variability during the past two millennia2013Ingår i: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 6, nr 5, s. 339-346Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.

  • 6. Akperov, Mirseid
    et al.
    Eliseev, Alexey V.
    Rinke, Annette
    Mokhov, Igor I.
    Semenov, Vladimir A.
    Dembitskaya, Mariya
    Matthes, Heidrun
    Adakudlu, Muralidhar
    Boberg, Fredrik
    Christensen, Jens H.
    Dethloff, Klaus
    Fettweis, Xavier
    Gutjahr, Oliver
    Heinemann, Günther
    Koenigk, Torben
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Sein, Dmitry
    Laprise, René
    Mottram, Ruth
    Nikiéma, Oumarou
    Sobolowski, Stefan
    Winger, Katja
    Zhang, Wenxin
    Future projections of wind energy potentials in the arctic for the 21st century under the RCP8.5 scenario from regional climate models (Arctic-CORDEX)2023Ingår i: Anthropocene, E-ISSN 2213-3054, Vol. 44, artikel-id 100402Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arctic has warmed more than twice the rate of the entire globe. To quantify possible climate change effects, we calculate wind energy potentials from a multi-model ensemble of Arctic-CORDEX. For this, we analyze future changes of wind power density (WPD) using an eleven-member multi-model ensemble. Impacts are estimated for two periods (2020-2049 and 2070-2099) of the 21st century under a high emission scenario (RCP8.5). The multi-model mean reveals an increase of seasonal WPD over the Arctic in the future decades. WPD variability across a range of temporal scales is projected to increase over the Arctic. The signal amplifies by the end of 21st century. Future changes in the frequency of wind speeds at 100 m not useable for wind energy production (wind speeds below 4 m/s or above 25 m/s) has been analyzed. The RCM ensemble simulates a more frequent occurrence of 100 m non-usable wind speeds for the wind-turbines over Scandinavia and selected land areas in Alaska, northern Russia and Canada. In contrast, non-usable wind speeds decrease over large parts of Eastern Siberia and in northern Alaska. Thus, our results indicate increased potential of the Arctic for the development and production of wind energy. Bias corrected and not corrected near-surface wind speed and WPD changes have been compared with each other. It has been found that both show the same sign of future change, but differ in magnitude of these changes. The role of sea-ice retreat and vegetation expansion in the Arctic in future on near-surface wind speed variability has been also assessed. Surface roughness through sea-ice and vegetation changes may significantly impact on WPD variability in the Arctic.

  • 7.
    Aldama Campino, Aitor
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Atmospheric and oceanic circulation from a thermodynamic perspective2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The climate system is continuously transporting and exchanging heat, freshwater, carbon and other tracers in different spatio-temporal scales. Therefore, analysing the system from a thermodynamic or biogeochemical framework is highly convenient. In this thesis the interaction between the ocean and the atmospheric circulation is analysed using thermodynamical and biogeochemical coordinates. Due to the dimensionality of the climate system stream functions are used to reduce this complexity and facilitate the understanding of the different processes that take place. The first half of this thesis, focuses on the interaction between the atmospheric and the ocean circulation from a thermodynamic perspective. We introduce the hydrothermohaline stream function which combines the atmospheric circulation in humidity-potential temperature (hydrothermal) space and the ocean circulation in salinity-temperature coordinates (thermohaline). A scale factor of 7.1 is proposed to link humidity and salinity coordinates. Future scenarios are showing an increase of humidity in the atmosphere due to the increase of temperatures which results in a widening of the hydrothermal stream function along the humidity coordinate. In a similar way, the ocean circulation in the thermohaline space expands along the salinity coordinate. The link between salinity and humidity changes is strongest at net evaporation regions where the gain of water vapour in the atmosphere results in a salinification in the ocean. In addition, the ocean circulation in latitude-carbon space is investigated. By doing so, we are able to distinguish the roles of different water masses and circulation pathways for ocean carbon. We find that the surface waters in the subtropical gyres are the main drivers of the meridional carbon transport in the ocean. By separating the carbon in its different constituents we show that the carbon transported by the majority of the water masses is a result of the solubility pump. The contribution of the biological pump is predominant in the deep Pacific Ocean. The effects of the Mediterranean Overflow Waters on the North Atlantic are discussed in the final part of the thesis.

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  • 8. Alexandridis, Nikolaos
    et al.
    Feit, Benjamin
    Kihara, Job
    Luttermoser, Tim
    May, Wilhelm
    Midega, Charles
    Öborn, Ingrid
    Poveda, Katja
    Sileshi, Gudeta W.
    Zewdie, Beyene
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Clough, Yann
    Jonsson, Mattias
    Climate change and ecological intensification of agriculture in sub-Saharan Africa – A systems approach to predict maize yield under push-pull technology2023Ingår i: Agriculture, Ecosystems & Environment, ISSN 0167-8809, E-ISSN 1873-2305, Vol. 352, artikel-id 108511Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Assessing effects of climate change on agricultural systems and the potential for ecological intensification to increase food security in developing countries is essential to guide management, policy-making and future research. ‘Push-pull’ technology (PPT) is a poly-cropping design developed in eastern Africa that utilizes plant chemicals to mediate plant–insect interactions. PPT application yields significant increases in crop productivity, by reducing pest load and damage caused by arthropods and parasitic weeds, while also bolstering soil fertility. As climate change effects may be species- and/or context-specific, there is need to elucidate how, in interaction with biotic factors, projected climate conditions are likely to influence future functioning of PPT. Here, we first reviewed how changes in temperature, precipitation and atmospheric CO2 concentration can influence PPT components (i.e., land use, soils, crops, weeds, diseases, pests and their natural enemies) across sub-Saharan Africa (SSA). We then imposed these anticipated responses on a landscape-scale qualitative mathematical model of maize production under PPT in eastern Africa, to predict cumulative, structure-mediated impacts of climate change on maize yield. Our review suggests variable impacts of climate change on PPT components in SSA by the end of the 21st century, including reduced soil fertility, increased weed and arthropod pest pressure and increased prevalence of crop diseases, but also increased biological control by pests’ natural enemies. Extrapolating empirical evidence of climate effects to predict responses to projected climate conditions is mainly limited by a lack of mechanistic understanding regarding single and interactive effects of climate variables on PPT components. Model predictions of maize yield responses to anticipated impacts of climate change in eastern Africa suggest predominantly negative future trends. Nevertheless, maize yields can be sustained or increased by favourable changes in system components with less certain future behaviour, including higher PPT adoption, preservation of field edge density and agricultural diversification beyond cereal crops.

  • 9.
    Aminjafari, Saeid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Brown, Ian A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Frappart, F.
    Papa, F.
    Blarel, F.
    Vahidi Mayamey, Farzad
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Jaramillo, Fernando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Distinctive Patterns of Water Level Change in Swedish Lakes Driven by Climate and Human Regulation2024Ingår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 60, nr 3, artikel-id e2023WR036160Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite having approximately 100,000 lakes, Sweden has limited continuous gauged lake water level data. Although satellite radar altimetry (RA) has emerged as a popular alternative to measure water levels in inland water bodies, it has not yet been used to understand the large-scale changes in Swedish lakes. Here, we quantify the changes in water levels in 144 lakes using RA data and in situ gauged measurements to examine the effects of flow regulation and hydroclimatic variability. We use data from several RA missions, including ERS-2, ENVISAT, JASON-1,2,3, SARAL, and Sentinel-3A/B. We found that during 1995–2022, around 52% of the lakes exhibited an increasing trend and 43% a decreasing trend. Most lakes exhibiting an increasing trend were in the north of Sweden, while most lakes showing a decreasing trend were in the south. Regarding the potential effects of regulation, we found that unregulated lakes had smaller trends in water level and dynamic storage than regulated ones. While the seasonal patterns of water levels in the lakes in the north are similar in regulated and unregulated lakes, in the south, they differ substantially. This study highlights the need to continuously monitor lake water levels for adaptation strategies in the face of climate change and understand the downstream effects of water regulatory schemes.

  • 10.
    Ampel, Linda
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Risberg, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Veres, Daniel
    Leng, Melanie
    Kaislahti Tillman, Päivi
    Diatom assemblage dynamics during abrupt climate change: The response oflacustrine diatoms to Dansgaard-Oeschger cycles during the last glacialperiod2010Ingår i: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, nr 2, s. 397-404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The sedimentary record from the paleolake at Les Echets in eastern France allowed a reconstruction of the lacustrine response to several abrupt climate shifts during the last glacial period referred to as Dansgaard-Oeschger (DO) cycles. The high-resolution diatom stratigraphy has revealed distinct species turnover events and large fluctuations in stable oxygen isotope values in diatom frustules, as a response to DO climate variability. More or less identical species compositions became re-established during each DO stadial and interstadial phases, respectively. However, the relative abundance of the most dominant species within these assemblages varies and might indicate differences in climatic conditions. Interstadial phases are characterized by identical species successions. Transitions from stadial to interstadial conditions show a distinct Fragilaria-Cyclotella succession, which resembles the diatom regime shifts that have been recognized in some lakes in the Northern Hemisphere since the mid-nineteenth century.

  • 11.
    Arra, Venni
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Storm Frequency in the Northern Baltic Sea Region and its Association to the North Atlantic Oscillation2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Storms can be both destructive and valuable at the same time. They expose coastal areas to various risks but can also enhance the supply of wind energy and provide marine ecosystems with oxygen rich water. As the North Atlantic Oscillation (NAO) is known to have a significant impact on the wind climate in Europe, investigating its interconnection to storm frequency and intensity under global warming circumstances in the Northern Baltic Sea region was of interest in this study. Wind speed data series of annual storm counts were obtained from five meteorological stations along with PC-based NAO values over the period 1960-2017. The data series were analysed in Microsoft Excel and modelled using a Poisson regression or negative binomial regression model in SPSS Statistics. The results display an unsystematic spatial pattern both in the association to the NAO as well as in the overall storm frequency. However, storm (≥ 21 m s-1) frequency has generally been decreasing, whereas the proportion of severe storms (≥ 24 m s-1) has slightly been increasing, suggesting a tendency toward stronger but fewer storms. Even though only certain data series display statistically significant findings (p ≤ .05), a majority of the winter storms and severe winter storms display a positive association, indicating that a higher NAOI is related to a greater number of winter storms. The spatial and temporal variability in the obtained results can partially be explained by storm tracks and prevalent wind directions. Nevertheless, inhomogeneities do presumably affect the wind speed observations through internal and external influences and changes related to the meteorological stations. Future research should, therefore, also consider integrating other storm related parameters, such as direct air pressure measurements, wave heights and storm surges, as well as implement different data homogenization methods and techniques.

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  • 12.
    Askjær, Thomas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Centennial Climate Variability2022Självständigt arbete på avancerad nivå (masterexamen), 30 poäng / 45 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Throughout earths history, the climate have always naturally varied due to both external forcings and internal mechanisms. With the outlook on future climate change, it is important to understand the climate system and this includes its natural variability. Depending on the driving mechanisms, the variability happens over different timescales. Among these is centennial variability, which still have unanswered questions. Studying centennial variability requires climate timeseries that are both long enough to encompass several cycles and detailed enough to resolve the variability signals. New data from long transient Holocene model simulations and recent efforts to compile large proxy databases now presents an opportunity to study centennial variability with better data foundation than earlier. To do so, this master thesis studies centennial variability in transient Holocene simulations from 9 models and 122 proxy records with a spectral analysis with the aim of finding the general signals related to cycle length, geographic dependencies and discuss the implications for the ongoing scientific discussion on the potential driver(s). The spectral analysis of the proxy records finds centennial variability significant from red noise in the majority of the records, with the highest concentration of cycle lengths around 120- 130 years, an average at 240-300 years, depending on the number of cycles included in the calculation, and no clear indication of it being dependent on which climate variable, although air temperature is the biggest group and influence the results the most. The analysis of the model global mean temperature (GMT) also finds centennial variability in all simulations with the highest concentration of cycle lengths around 120-150 years and an average just slightly above that. A good agreement between model and proxy data is thereby indicated, although the spread is slightly larger for the proxy data, but this is also a more diverse collection of data than the models. There is also a good agreement in the lack of latitudinal dependencies, where centennial variability is found at all latitudes of the model data (6 bands with a combined global coverage is analysed) and no clear differentiation is found between the proxy records at different latitudes. However, all the model data have most spectral density distributed over the 90N to 60N latitude band, which indicates either a particular variability sensitivity or potential driving mechanisms in this region. Four of the models also have differentiated/single forcings simulations and the spectral analysis of the GMT in all of these also reveals significant centennial variability with cycle lengths between 100-200 years. The simulations where only orbital forcing also show this and so the different forcings seem to induce some variability to the system, but none can be said to be the main driver based on the spectral analysis. This also includes solar irradiance, which long have been hypothesised to drive centennial variability, as all the simulations without this forcing, which includes some of the full forcing simulations as well, all have significant centennial variability. The results instead indicate that centennial variability is internally driven and that the Arctic is a region of interest for this aspect. The conclusions is not without uncertainties, as both proxies and model simulations have uncertainties, but when analysing with a largely uniform approach on a large data collection, there is good evidence of centennial variability with cycle lengths around 100-200 years across the entire range of available Holocene paleoclimate data

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  • 13.
    Asokan, Shilpa M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Appendix to Paper V: Climate model performance versus basin-scalehydro-climatic dataManuskript (preprint) (Övrigt vetenskapligt)
  • 14.
    Asokan, Shilpa M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Irrigation effects on hydro-climatic change: Basin-wise water balance-constrained quantification and cross-regional comparison2014Ingår i: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 35, nr 3, s. 879-895Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Hydro-climatic changes driven by human land and water use, including water use for irrigation, may be difficult to distinguish fromthe effects of global, natural and anthropogenic climate change. This paper quantifies and compares the hydro-climatic change effects ofirrigation using a data-driven, basin-wise quantification approach in two different irrigated world regions: the Aral Sea drainage basinin Central Asia, and the Indian Mahanadi River Basin draining into the Bay of Bengal. Results show that irrigation-driven changesin evapotranspiration and latent heat fluxes and associated temperature changes at the land surface may be greater in regions withsmall relative irrigation impacts on water availability in the landscape (here represented by the MRB) than in regions with severe suchimpacts (here represented by the Aral region). Different perspectives on the continental part of Earth’s hydrological cycle may thus implydifferent importance assessment of various drivers and impacts of hydro-climatic change. Regardless of perspective, however, actualbasin-wise water balance constraints should be accounted to realistically understand and accurately quantify continental water change.

  • 15.
    Asokan, Shilpa M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Dutta, Dushmanta
    Analysis of water resources in the Mahanadi River Basin, India under projected climate conditions2008Ingår i: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 22, nr 18, s. 3589-3603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper presents the outcomes of a study conducted to analyse water resources availability and demand in the Mahanadi River Basin in India under climate change conditions. Climate change impact analysis was carried out for the years 2000, 2025, 2050, 2075 and 2100, for the months of September and April (representing wet and dry months), at a sub-catchment level. A physically based distributed hydrologic model (DHM) was used for estimation of the present water availability. For future scenarios under climate change conditions, precipitation output of Canadian Centre for Climate Modelling and Analysis General Circulation Model (CGCM2) was used as the input data for the DHM. The model results show that the highest increase in peak runoff (38%) in the Mahanadi River outlet will occur during September, for the period 2075-2100 and the maximum decrease in average runoff (32·5%) will be in April, for the period 2050-2075. The outcomes indicate that the Mahanadi River Basin is expected to experience progressively increasing intensities of flood in September and drought in April over the considered years. The sectors of domestic, irrigation and industry were considered for water demand estimation. The outcomes of the analysis on present water use indicated a high water abstraction by the irrigation sector. Future water demand shows an increasing trend until 2050, beyond which the demand will decrease owing to the assumed regulation of population explosion. From the simulated future water availability and projected water demand, water stress was computed. Among the six sub-catchments, the sub-catchment six shows the peak water demand. This study hence emphasizes on the need for re-defining water management policies, by incorporating hydrological response of the basin to the long-term climate change, which will help in developing appropriate flood and drought mitigation measures at the basin level.

  • 16.
    Asokan, Shilpa M.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Jarsjö, Jerker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Vapor flux by evapotranspiration: effects of changes in climate, land-use and water-use2010Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, nr D24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Enhanced evapotranspiration (ET) over irrigated land and associated latent heat flux change can modify the climate. Model studies of such climate change effects of irrigation are commonly based on land use parameterizations, in terms of irrigated land area, or land area equipped for irrigation. Actual ET change, however, may also be driven by water use change in addition to land use change. This study quantifies and compares ET changes due to changes in climate, land use, and water use from the preirrigation period 1901–1955 to the recent period 1990–2000 (with irrigation) for the example case of Mahanadi River Basin (MRB) in India. The results show that actual water use per unit area of irrigated land may vary greatly over a hydrological drainage basin. In MRB, much higher water use per irrigated land unit in the downstream humid basin parts leads to higher vapor flux by ET, and irrigation‐induced ET flux change, than in the upstream, water‐stressed basin parts. This is consistent with water supply limitations in water‐stressed basins. In contrast, the assumption in land use−based models that irrigation maintains high soil moisture contents can imply higher modeled water use and therefore also higher modeled ET fluxes under dry conditions than under humid conditions. The present results indicate water use as an important driver of regional climate change, in addition to land use and greenhouse gas‐driven changes.

  • 17.
    Axelsson, Josefine
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Interglacial climates in proxies and models: Utilizing sampled oxygen isotopes and model simulations to understand past Indian summer monsoon variability2024Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Studier av jordens klimatsystem, inklusive de komplexa mekanismerna som driver de globala monsunsystemen, utgör en grundläggande del av forskningen inom klimatvetenskaperna. Monsuner, som är livsviktiga för miljarder människor världen över, representerar komplexa atmosfäriska fenomen som påverkas av ett brett spektrum av globala faktorer. Dessa inkluderar orbitala förändringar som påverkar jordens exponering för solstrålning samt den naturliga variabiliteten i vårt klimatsystem. Specifikt är den Indiska sommarmonsunen (ISM) av särskilt vetenskapligt intresse på grund av dess inverkan på klimatet, jordbruket och tillgängligheten till vatten i Sydasien. Att förstå ISM:s variabilitet genom historien och dess potentiella förändringar i framtiden är avgörande för att kunna förutsäga och anpassa sig till kommande klimatförändringar i denna region.

    I ett försök att bidra till denna vetenskapliga utmaning har denna avhandling använt sig av en kombination av naturliga arkiv och klimatmodellering. Genom att analysera stabila vattenisotoper från nederbörd och stalagmiter, tillsammans med avancerade simuleringar från klimatmodeller, har vi strävat efter att förstå ISM:s respons på naturliga drivkrafter under nyckelperioder såsom den senaste interglaciala perioden (127 000 år sedan), holocen (11 700 år sedan till nutid) och det senaste årtusendet. Vår forskning visar att ISM är känslig för en rad både lokala och globala faktorer, såsom lokala geografiska egenskaper och avlägsna atmosfäriska förhållanden på ISM:s årliga variabilitet. Monsunens respons på orbitala förändringar, såsom varierande avstånd och vinkel till solen, är särskilt framträdande, vilket understryker den direkta kopplingen mellan rymd- och klimatdynamik.

    En viktig upptäckt i vår forskning har varit skillnaderna mellan isotopsignaler från klimatmodeller och de i stalagmiter. Dessa skillnader ifrågasätter nuvarande förståelse för hur väl både proxy och modeller återspeglar de naturliga drivkrafternas inverkan på klimatsystemet. Särskilt framgår att nuvarande klimatmodeller kanske inte fullständigt återspeglar de regionala och globala signalerna eller den temporala variabiliteten av δ18O, vilket pekar på ett behov av att finjustera dessa modeller. Det är avgörande att modellerna förfinas för att noggrant återspegla de komplexa fenomen som observeras i de naturliga arkiven. Dessutom belyser vår forskning behovet av att förbättra förståelsen och karaktäriseringen av osäkerheter i proxydata, särskilt när det gäller stalagmiters åldersosäkerheter.

    Denna avhandling framhäver vikten av att överbrygga klyftan mellan insikter som erhålls från proxydata och resultaten från klimatmodellsimuleringar. Genom att sammanföra dessa två forskningsgrenar kan vi inte bara utöka vår kunskap om det historiska klimatet utan också förbättra vår förmåga att göra mer precisa klimatprognoser och projektioner för framtiden. Detta understryker den oumbärliga roll som tvärvetenskaplig forskning spelar för att skapa förståelse kring komplexa utmaningar jorden står inför.

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    Interglacial climates in proxies and models: Utilizing sampled oxygen isotopes and model simulations to understand past Indian summer monsoon variability
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  • 18.
    Axelsson, Josefine
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Gao, Jing
    Eckhardt, Sabine
    Cassiani, Massimo
    Chen, Deliang
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    A Precipitation Isotopic Response in 2014-2015 to Moisture Transport Changes in the Central Himalayas2023Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 128, nr 13, artikel-id e2023JD038568Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of moisture transport and sources on precipitation stable isotopes (d(18)O and d-excess) in the central Himalayas are crucial to understanding the climatic archives. However, this is still unclear due to the lack of in-situ observations. Here we present measurements of stable isotopes in precipitation at two stations (Yadong and Pali) in the central Himalayas during 2014-2015. Combined with simulations from the dispersion model FLEXPART, we investigate effects on precipitation stable isotopes related to changes in moisture sources and convections in the region, and possible influence by El Nino. Our results suggest that the moisture supplies related to evaporation over northeastern India and moisture losses related to convective activities over the Bay of Bengal (BoB) and Bangladesh region play important roles in changes in d(18)O and d-excess in precipitation in the Yadong Valley. Outgoing longwave radiation and moisture flux divergence analysis further confirm that the contribution from continental evaporation dominates the moisture supply in the central Himalayas with a lesser contribution from convection over the BoB during the 2015 monsoon season compared with 2014. A change in the altitude effect is observed in 2015, which is more significant than the temperature and precipitation amount effect during the observation period. These findings provide valuable insights into climatic interpretations of paleo-isotopic archives with an isotopic response to changes in moisture transport to the central Himalayas.

  • 19.
    Axelsson, Pia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Minskad trädtillväxt under Lilla sitiden?: En dendroklimatologisk jämförelse mellan nutid och 1600-talet invid trädgränsen i norra Skandinavien2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    During the period called Little Ice Age (1400 ~ 1900) the climate of northern Europe was in an annual year-basis overall colder than it was before and after that period. The numbers of short, cold and rainy summers and long, bitter-cold winters where often repetitive under the approximately 500-years the period lasted. In Scandinavia, the coldest time during this period is estimated to have started around the end of the 16th century and lasted to the beginning of the 18th century. Trees growing at the tree-line are limited by temperature for their annual growth and hence showing differences of growth during changes in the climate,  a method called dendroclimatology. The variations of growth can be read in the tree-rings either by analyze the width of the ring or by look into the density of the wood and is used to reconstruct past climates. The aim of this study is to investigate how the tree-growth responded to the colder temperatures compared to today. Trees (Scots pine) close to the tree-line in northern Scandinavia where used to enhance the temperature signal in the data.  The proxy used is the growth density (MXD – maximum latewood density). The result reveals that during the coldest century, the trees show a larger number of negative growth-years with comparison with the 20th century and the negative and positive growth follows a more united trend. The result also shows a great number of negative growth-years at the end of the Little Ice Age, with a lot of extreme low growth - indexes (lower than -1.5). The conclusion then leans towards a cooler climate with overall lower temperatures under the 17th century compared to 1900-2004. 

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  • 20.
    Axelsson, Sophia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    How climate change impacts the habitat building vegetation in the Baltic Sea: How are the species bladderwrack & common eelgrass impacted by climate change in the Baltic Sea?2022Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Världens hav förändras utan tvekan av den globala uppvärmningen, vilket påverkar alla arter och leder till ekosystem förändringar. Den övergripande låga biologiska mångfalden i Östersjön leder till känsliga unika förhållanden. Att förstå hur klimatförändringarna i Östersjön kommer att påverka nyckelarter är viktigt för att förstå hur Östersjöns kustmiljö kommer att se ut i framtiden. Fucus vesiculosus och Zostera marina, är viktiga habitatsbildande växter i Östersjön, som bygger upp majoriteten av ekosystemen vid kusterna på steniga och sandiga bottnar. Hur påverkas dessa arter av klimatförändringar i Östersjön? Resultatet visade att tillväxten av både Fucus och Zostera stimuleras under större delen av året med stigande temperaturer, men under sommaren hämmar värmeböljor växterna, vilket ökar dödligheten. Huvudslutsatserna är att Fucus kommer att vandra mer söderut, eftersom Östersjön med största sannolikhet kommer att bli sötare från norr, och Zostera kommer fortsätta trivas om näringsmängden minskar. Båda arterna kommer drabbas av dödsfall under värmeböljor på sommaren. 

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    HowClimateChangeImpactsTheHabitatBuildingVegetationInTheBalticSea
  • 21.
    Azam, Monirul
    Stockholms universitet, Juridiska fakulteten, Juridiska institutionen.
    Are the UNFCCC Paris Agreement and the TRIPS Agreement Facilitating Access to and Transfer of Climate Technologies for the LDCs?2021Ingår i: Manchester Journal of International Economic Law, E-ISSN 1742-3945, Vol. 18, nr 3, s. 327-369Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article evaluates the effectiveness of the technology transfer provisions under the United Nations Framework Convention on Climate Change (UNFCCC), Kyoto Protocol, and Paris Agreement and under the Trade-Related Aspects of Intellectual Property Rights (TRIPS) Agreement, to facilitate access to and transfer of climate technologies for the least developed countries (LDCs) through a case study on Bangladesh (which has been selected considering its serious vulnerability to climate change and as one of the most active LDC in technology transfer during climate negotiations and TRIPS Council meetings). This article concludes that the LDCs should indicate their technology needs in their Nationally Determined Contributions (NDC) using an integrated, collaborative approach, including financing for climate technologies and capacity-building indicating their specific technology transfer needs. The TRIPS Council under the TRIPS Agreement could introduce a comprehensive review mechanism for evaluating the technology transfer support provided by the developed countries to the LDCs. The author proposes to develop a database of urgently needed climate technologies and establish a neglected climate technology initiatives network to facilitate access and transfer of urgently needed climate technologies for the LDCs.

  • 22. Azcárate, Juan
    et al.
    Balfors, Berit
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Bring, Arvid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Transboundary approach proposal for sustainable and climate change adaptation strategies in the Arctic2012Konferensbidrag (Övrigt vetenskapligt)
  • 23. Balathandayuthabani, Sivakiruthika
    et al.
    Wallin, Marcus B.
    Klemedtsson, Leif
    Crill, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Bastviken, David
    Aquatic carbon fluxes in a hemiboreal catchment are predictable from landscape morphology, temperature, and runoff2023Ingår i: Limnology and Oceanography Letters, E-ISSN 2378-2242, Vol. 8, nr 2, s. 313-322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aquatic networks contribute greenhouse gases and lateral carbon (C) export from catchments. The magnitudes of these fluxes exceed the global land C sink but are uncertain. Resolving this uncertainty is important for understanding climate feedbacks. We quantified vertical methane (CH4) and carbon dioxide (CO2) emissions from lakes and streams, and lateral export of dissolved inorganic and organic carbon from a hemiboreal catchment for 3 yr. Lateral C fluxes dominated the total aquatic C flux. All aquatic C fluxes were disproportionately contributed from spatially restricted areas and/or short-term events. Hence, consideration of local and episodic variability is vital. Temperature and runoff were the main temporal drivers for lake and stream C emissions, respectively. Whole-catchment aquatic C emissions scaled linearly with these drivers within timeframes of stable land-cover. Hence, temperature and runoff increase across Northern Hemisphere humid areas from climate change may yield proportional increases in aquatic C fluxes. 

  • 24.
    Barrientos, Natalia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Arctic Ocean benthic foraminifera preservation and Mg/Ca ratios: Implications for bottom water palaeothermometry2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Reconstructions of Arctic Ocean palaeotemperatures are needed to disentangle natural variability from anthropogenic changes and understand the role of ocean heat transport in forcing or providing feedbacks on Arctic climate change. Despite known complications with calcareous microfossil preservation in Arctic Ocean sediments, calcareous benthic foraminifera can be common in interglacial sequences. However, thus far they have been underutilized in palaeoceanographic studies. This thesis explores the application of the Mg/Ca palaeothermometry proxy for reconstructing bottom water temperatures (BWT) in the Arctic Ocean during the late Quaternary. This method, which is supported by previous empirical studies demonstrating a strong temperature control on trace Mg inclusion into foraminiferal shell calcite, has been applied in many ocean regions and time intervals. Until now its application in the Arctic Ocean has been sparingly explored.

    The results of this doctoral thesis are based on benthic foraminifera retrieved from marine sediment cores covering a wide geographical Arctic Ocean area including both the shallow and vast continental shelves and slopes to the intermediate-to-deep waters of the Lomonosov Ridge and Morris Jesup Rise. These provide the first benthic foraminifera Mg/Ca ratios from the central Arctic Ocean region. In the first study, mechanisms that could affect Mg incorporation in Arctic benthic foraminifera are investigated using oceanographic field data and six 'live' modern Arctic species (Elphidium clavatum, Nonionella labradorica, Cassidulina neoteretis, Oridorsalis tener, Cibicidoides wuellerstorfi and Quinqueloculina arctica). The result is new species-specific Mg/Ca–BWT field calibrations that provide important constraints at the cold end of the BWT spectrum (-2 to 1°C) (Paper I). Using the new Mg/Ca–BWT equation for E. clavatum, a palaeotemperature record was generated for the late Holocene (past ca. 4100 yr) from the western Chukchi Sea. The data showed BWT fluctuations from -2 to 1°C that are interpreted as showing pulses of warmer Pacific water inflow at 500–1000 yr periods, thus revealing multi-centennial variability in heat transport into the Arctic Ocean driven by low latitude forcings (Paper II). Complications with foraminiferal calcite preservation that limit Mg/Ca palaeothermometry in the Arctic were discovered and these are tackled in two additional papers. Anomalously high Mg content in benthic foraminifera from the central Arctic Ocean is linked to diagenetic contamination as a result of the unique oceanographic, sedimentary and geochemical environment (Paper III). Lastly, the dramatic post-recovery dissolution of foraminifera from a Chukchi Shelf sediment core during core storage is investigated and attributed to acidification driven by sulphide oxidation in this organic rich and calcite poor shelf setting (Paper IV).

    The findings of this thesis demonstrate that benthic foraminiferal Mg/Ca-palaeothermometry can be applied in the Arctic Ocean and capture small BWT change (on the order of -2 to 2°C) even at low temperatures. In practice, preservational complexities can be limiting and require special sample handling or analysis due to the high potential for diagenetic contamination in the central Arctic Ocean and rapid post coring calcite dissolution in the seasonally productive shelf seas. This Ph.D. project is a component of the multidisciplinary SWERUS-C3 (Swedish-Russian-US Arctic Ocean Climate-Cryosphere- Carbon Interactions) project that included an expedition with Swedish icebreaker Oden to the East Siberian Arctic Ocean.

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    Arctic Ocean benthic foraminifera preservation and Mg/Ca ratios: Implications for bottom water palaeothermometry
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  • 25.
    Barrientos, Natalia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Coxall, Helen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Lear, Caroline
    Pearce, Christof
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Muschitiello, Francesco
    O'Regan, Matt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Stranne, Christian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    de Boer, Agatha
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Cronin, Thomas
    Semiletov, Igor
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Late Holocene variability in Arctic Ocean Pacific Water inflow through the Bering StraitManuskript (preprint) (Övrigt vetenskapligt)
  • 26.
    Barrientos, Natalia
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Lear, Caroline H.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Stranne, Christian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    O'Regan, Matt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Cronin, Thomas M.
    Gukov, Aleksandr Y.
    Coxall, Helen K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Arctic Ocean benthic foraminifera Mg/Ca ratios and global Mg/Ca-temperature calibrations: New constraints at low temperatures2018Ingår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 236, s. 240-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We explore the use of Mg/Ca ratios in six Arctic Ocean benthic foraminifera species as bottom water palaeothermometers and expand published Mg/Ca-temperature calibrations to the coldest bottom temperatures (<1 °C). Foraminifera were analyzed in surface sediments at 27 sites in the Chukchi Sea, East Siberian Sea, Laptev Sea, Lomonosov Ridge and Petermann Fjord. The sites span water depths of 52–1157 m and bottom water temperatures (BWT) of −1.8 to +0.9 °C. Benthic foraminifera were alive at time of collection, determined from Rose Bengal (RB) staining. Three infaunal and three epifaunal species were abundant enough for Mg/Ca analysis. As predicted by theory and empirical evidence, cold water Arctic Ocean benthic species produce low Mg/Ca ratios, the exception being the porcelaneous species Quinqueloculina arctica. Our new data provide important constraints at the cold end (<1 °C) when added to existing global datasets. The refined calibrations based on the new and published global data appear best supported for the infaunal species Nonionella labradorica (Mg/Ca = 1.325 ± 0.01 × e^(0.065 ± 0.01 × BWT), r2 = 0.9), Cassidulina neoteretis (Mg/Ca = 1.009 ± 0.02 × e^(0.042 ± 0.01 × BWT), r2 = 0.6) and Elphidium clavatum (Mg/Ca = 0.816 ± 0.06 + 0.125 ± 0.05 × BWT, r2 = 0.4). The latter is based on the new Arctic data only. This suggests that Arctic Ocean infaunal taxa are suitable for capturing at least relative and probably semi-quantitative past changes in BWT. Arctic Oridorsalis tener Mg/Ca data are combined with existing O. umbonatus Mg/Ca data from well saturated core-tops from other regions to produce a temperature calibration with minimal influence of bottom water carbonate saturation state (Mg/Ca = 1.317 ± 0.03 × e^(0.102 ± 0.01 BWT), r2 = 0.7). The same approach for Cibicidoides wuellerstorfi yields Mg/Ca = 1.043 ± 0.03 × e^(0.118 ± 0.1 BWT), r2 = 0.4. Mg/Ca ratios of the porcelaneous epifaunal species Q. arctica show a clear positive relationship between Mg/Ca and Δ[CO32−] indicating that this species is not suitable for Mg/Ca-palaeothermometry at low temperatures, but may be useful in reconstructing carbonate system parameters through time.

  • 27.
    Bennich, Therese
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Belyazid, Salim
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Stjernquist, Ingrid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Diemer, Arnaud
    Seifollahi-Aghmiuni, Samaneh
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Kalantari, Zahra
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. KTH Royal Institute of Technology, Sweden.
    The bio-based economy, 2030 Agenda, and strong sustainability – A regional-scale assessment of sustainability goal interactions2021Ingår i: Journal of Cleaner Production, ISSN 0959-6526, E-ISSN 1879-1786, Vol. 283, artikel-id 125174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Policy-makers face the challenge of assessing and implementing sustainability measures, while also dealing with parallel and sometimes conflicting policy agendas, long-term policy impacts, and contested interpretations of sustainability. To support evidence-based decision-making in this context, this paper presents the results from an integrated assessment of sustainability goal interactions. Links between the bio-based economy, the 2030 Agenda, and the so-called strong sustainability paradigm were explored in a regional-scale case. The analysis focused primarily on developments in the forestry and energy sectors. Direct trade-offs and synergies as well as broader systemic impacts were identified. The results show how goals from the bio-based economy, 2030 Agenda and strong sustainability paradigm are mutually interacting. Positive interactions were found within two clusters of goals, offering coherent and synergetic transition pathways within these. The first cluster encompasses developments toward intensified forestry, renewable energy, and closed-loop production systems. The second pathway supports diversified forestry and protection of critical natural capital. However, while internally coherent, trade-offs were identified between these goal clusters, demonstrating the difficulty in simultaneously making progress on goals belonging to different sustainability agendas. The results also stress the need for disaggregation and long-term assessments to identify trade-offs and synergies. Finally, the analysis highlights the theoretical potential but practical challenges of implementing the bio-based economy and 2030 Agenda in a way that adheres to strong sustainability. The analytical framework used in the present study may be adapted and applied to other decision-making contexts. It is particularly useful in settings characterized by uncertainty and unstructured problem spaces.

  • 28. Benze, Susanne
    et al.
    Randall, Cora E.
    Karlsson, Bodil
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Harvey, V. Lynn
    DeLand, Matthew T.
    Thomas, Gary E.
    Shettle, Eric P.
    On the onset of polar mesospheric cloud seasons as observed by SBUV2012Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, s. D07104-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes an investigation using data from the Solar Backscatter Ultraviolet (SBUV) satellite instruments to explore and understand variations in the timing of the onset of Polar Mesospheric Cloud (PMC) seasons. Previous work has shown that for several recent southern hemisphere (SH) seasons, the PMC season onset was controlled by the timing of the shift from winter to summer zonal wind flow in the SH stratosphere. We extend the analysis of PMC season onset to 28 years of SBUV observations, including both hemispheres. A multiple linear regression analysis of SBUV data from 1984 to 2011 suggests that the SH PMC season onset is delayed by one day for every day that the zonal wind at 65 degrees S and 50 hPa (similar to 20 km) remains in a winter-like state. In addition, we find that the solar cycle plays a role: The SH season onset is delayed by about ten days at solar maximum compared to solar minimum. In the NH, the PMC season onset is delayed by similar to 7 days at solar maximum compared to solar minimum; variations in the NH stratospheric wind, however, are not correlated with the NH onset date. On the other hand, inter-hemispheric teleconnections are important in the NH; a one-day shift in the NH season onset corresponds to a shift of similar to 1.4 m/s in the SH stratospheric wind at 60.0 degrees S and 20 hPa (similar to 26 km). Neither the NH nor the SH season onset date is correlated with the Quasi-Biennial Oscillation, North Atlantic Oscillation, Arctic Oscillation, or El Nino Southern Oscillation.

  • 29. Berghuijs, Wouter R.
    et al.
    Collenteur, Raoul A.
    Jasechko, Scott
    Jaramillo, Fernando
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Luijendijk, Elco
    Moeck, Christian
    van der Velde, Ype
    Allen, Scott T.
    Groundwater recharge is sensitive to changing long-term aridity2024Ingår i: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 14, s. 357-363Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sustainable groundwater use relies on adequate rates of groundwater recharge, which are expected to change with climate change. However, climate impacts on recharge remain uncertain due to a paucity of measurements of recharge trends globally. Here we leverage the relationship between climatic aridity and long-term recharge measurements at 5,237 locations globally to identify regions where recharge is most sensitive to changes in climatic aridity. Recharge is most sensitive to climate changes in regions where potential evapotranspiration slightly exceeds precipitation, meaning even modest aridification can substantially decrease groundwater recharge. Future climate-induced recharge changes are expected to be dominated by precipitation changes, whereby changes in groundwater recharge will be amplified relative to precipitation changes. Recharge is more sensitive to changes in aridity than global hydrological models suggest. Consequently, the effects of climatic changes on groundwater replenishment and their impacts on the sustainability of groundwater use by humans and ecosystems probably exceed previous predictions.

  • 30.
    Berglund, Sara
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tracing pathways in the ocean circulation: A temperature and salinity perspective2021Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The ocean circulation plays an essential role in our climate system. It redistributes heat, salt, carbon and other tracers across the globe, making the climate of Earth more moderate. This thesis targets density differences that are driving the ocean circulation. These differences are caused by changes in temperature and salinity. The analysis is based on the usage of Lagrangian trajectories simulated with velocity fields from an Earth System Model. The Lagrangian approach opens up for the possibility to follow specific water paths and water masses. The results herein provide a new insight to specific circulation patterns in the ocean, and which regions that play an important role in controlling temperature and salinity changes.

    In the first two articles, the Lagrangian divergence is introduced. It shows the geographical distribution of heat and salt changes of a simulated water mass. Using this, we are able to show that the northward flowing water in the Atlantic Ocean cools and freshens in the North Atlantic Subtropical Gyre, the Gulf Stream and the North Atlantic Current. Similarly, we show that the water flowing from the Drake Passage, following the Antarctic Circumpolar Current (ACC) and moving northwards into the Atlantic, Pacific and Indian oceans, transforms from cold and fresh to warm and saline. This warming and salinification are a result of, not only air-sea fluxes, but also interior mixing.

    In the third study, we show that 70% of the water flowing northwards as part of the Atlantic Meridional Overturning Circulation circuits the North Atlantic Subtropical Gyre at least once before it continues northwards. In the gyre, the water spirals downwards as it gets denser, due to a combination of air-sea fluxes and interior mixing. These results bring a new perspective on the Subtropical Gyre's role to the circulation patterns of the Atlantic Meridional Overturning Circulation.

    In the last part of this thesis, the circulation in the North Atlantic Ocean is traced into four different pathways. The pathways are visualised geographically together with their change in temperature, salinity and density. With this, we are able to show that the northward flowing water in the Atlantic Ocean exchanges heat and salt with the colder and fresher waters circulating the Subpolar Gyre.

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  • 31.
    Berglund, Sara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Döös, Kristofer
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Groeskamp, Sjoerd
    NIOZ Royal Netherlands Institute for Sea Research, Den Burg, Texel, The Netherlands.
    McDougall, Trevor J.
    School of Mathematics and Statistics, University of New South Wales, Australia.
    The Downward Spiralling Nature of the North Atlantic Subtropical GyreManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The Atlantic Meridional Overturning Circulation (AMOC) regulates the heat distribution and climate of Earth. Here we identify a new feature of the circulation within the North Atlantic Subtropical Gyre that is associated with the northward flowing component of the AMOC.We find that 70% of the water that flows northwards as part of the AMOC circulates the Gyre at least once before it can continue northwards.These circuits are needed to achieve an increase of density and depth through a combination of air-sea interaction and interior mixing processes, before water can escape the latitudes of the Gyre and join the northern upper branch of the AMOC.This points towards an important role of the Gyre circulations in determining the strength and variability of the AMOC and the northward heat transport.Understanding this newly identified role of the North Atlantic Subtropical Gyre is needed to properly represent future changes of the AMOC. 

  • 32.
    Berntell, Ellen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Understanding West African Monsoon Variability: Insights from Paleoclimate Modelling of Past Warm Climates2023Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The Sahel, a water-vulnerable region in West Africa, relies heavily on rainfed agriculture. The region experienced pronounced droughts during the 20th Century, emphasising the socio-economic importance of understanding the drivers of the rainfall variability. However, future rainfall projections remain uncertain due to the complex nature of the West African Monsoon (WAM), which is influenced by internal climate variability, external forcing, and feedback processes. Limited observational records in West Africa and the need for longer time series further complicate the understanding of these drivers.

     This thesis uses paleoclimate modelling to investigate internal and external drivers of monsoon variability in West Africa across four distinct periods. Our study confirms that atmosphere-only model simulations can capture the observed multidecadal rainfall variability in the 20th Century, even though reanalyses struggle to reproduce the correct timing. Analysis of a last millennium simulation using the Earth System Model EC-Earth3 identified two drivers of multidecadal rainfall variability, accounting for 90% of the total co-variability between the West African rainfall and Atlantic sea surface temperatures (SSTs). This finding strengthens our understanding of SST-WAM relationships observed during the 20th Century. An ensemble of climate model simulations (PlioMIP2) shows that high CO2 levels and a different paleogeography during the mid-Pliocene Warm Period led to increased rainfall and a strengthened WAM. Our study emphasised vegetation's crucial role in enhancing the monsoon in past climates.

     However, simulations forced with prescribed vegetation only capture a one-directional forcing. A mid-Holocene simulation using an Earth System Model with dynamic vegetation revealed that vegetation feedbacks strengthen the WAM response to external orbital forcing but are insufficient to shift the monsoon northward or increase vegetation cover over the Sahara. These results reveal a dry bias and under-representation of simulated vegetation compared to proxy records, highlighting the importance of model development and the need for additional feedback processes in driving an enhanced, northward WAM and extending vegetation to the Sahara.

     Overall, this thesis advances our understanding of the drivers of West African monsoon variability and provides valuable insights for improving future rainfall projections in this vulnerable region.

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  • 33.
    Berntell, Ellen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI). Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Mid-Holocene West African monsoon rainfall enhanced in EC-Earth simulation with dynamic vegetation feedback2024Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Proxy records have shown that the Mid-Holocene was a period of humid conditions across West Africa, with an enhanced West African Monsoon (WAM) and vegetated conditions in areas currently characterized by desert, often referred to as the Green Sahara. However, General Circulation Models regularly struggle with recreating this strengthened Mid-Holocene monsoon in West Africa. Vegetation feedbacks has long been viewed as an essential process modulating the monsoon variability in West Africa, and simulations using prescribed vegetation to recreate a Green Sahara have shown a strengthened WAM and increased rainfall. However, simulations with prescribed vegetation in Sahara represent an idealized vegetation cover and do not take any environmental heterogeneity into account. Furthermore, this only represents a one-directional forcing by the vegetation on the climate rather than the full vegetation feedback. To address this, we have simulated the Mid-Holocene (similar to 6 ka) climate using the Earth System Model EC-Earth3-Veg. The results show that coupled dynamic vegetation reproduces an apparent enhancement of the WAM, with the summer rainfall in the Sahel region increasing by 15% compared to simulations with a prescribed modern vegetation cover. Vegetation feedbacks enhance the warming of the Sahara region, deepens the Sahara Heat Low, results in increased rainfall and strengthens monsoonal flow across West Africa. However, the enhancement is still below what can be viewed in proxy reconstructions, highlighting the role of model limitation and biases and the importance of investigating other processes, such as the interactive aerosol-albedo feedback.

  • 34.
    Berntell, Ellen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Mid-Holocene West African Monsoon Rainfall enhanced in high-resolution EC-Earth simulation with dynamic vegetation feedbackManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Proxy records have shown that the Mid-Holocene was a period of humid conditions across West Africa, with an enhanced West African Monsoon (WAM) and vegetated conditions in areas currently characterized by desert, often referred to as the Green Sahara. However, General Circulation Models regularly struggle with recreating this strengthened Mid-Holocene monsoon in West Africa. The vegetation-albedo feedback has long been viewed as an essential process modulating the monsoon variability in West Africa, and simulations using prescribed vegetation to recreate a Green Sahara have shown a strengthened WAM and increased rainfall. However, these simulations represent an idealized vegetation cover and do not take any environmental heterogeneity into account. Furthermore, this only represents a one-directional forcing by the vegetation on the climate rather than the vegetation-albedo feedback. Using idealized vegetation cover might therefore over-/underestimate the changes of the WAM, as well as over-/understate the importance of the vegetation feedback. To address this, we have simulated the Mid-Holocene (~6 ka) climate using the high-resolution Earth System Model EC-Earth3-Veg. The results show that coupled dynamic vegetation reproduces an apparent enhancement of the WAM, with the summer rainfall in the Sahel region increasing by 15% compared to simulations with a prescribed modern vegetation cover. Vegetation feedbacks enhance the warming of the Sahara region, deepens the Sahara Heat Low, results in increased rainfall and strengthens monsoonal flow across West Africa. However, the enhancement is still below what can be viewed in proxy reconstructions, highlighting the importance of investigating other processes, such as the interactive aerosol-albedo feedback.

  • 35. Bian, Jianpu
    et al.
    Räisänen, Jouni
    Zhang, Qiong
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Mechanisms for African easterly wave changes in simulations of the mid-Holocene2023Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 61, nr 7-8, s. 3165-3178Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mid-Holocene was a warm period with significantly amplified precipitation in North Africa, and a northward shifted Western African Monsoon during boreal summer. We conduct simulations for the pre-industrial and mid-Holocene periods to investigate the connection between summer rainfall variability and changes of African easterly waves (AEWs) during the mid-Holocene. Summer rainfall increases and migrates northward during the mid-Holocene, but the magnitude of change fails to reconcile the discrepancy with mid-Holocene proxy evidence, possibly due to no prescribed vegetation change in our simulations. The spectrum of summer rainfall over the Sahel and West Africa reveals enhanced synoptic time scale (3-to-6 days) variability during the mid-Holocene, which is consistent with the enhanced AEW activity influence. Specifically, the southern AEW track strengthens and migrates poleward during the mid-Holocene period, which modulates summer rainfall over the Sahel and West Africa. By comparison, the northern AEW track changes less and produces a minor contribution to rainfall changes in those regions. We find enhanced baroclinic and barotropic instabilities to promote the AEW activity during the mid-Holocene, with a doubling of the eddy kinetic energy of the meridional wind from that in PI, and baroclinic energy conversion plays a more important role. Stronger low-level meridional thermal gradients increase moisture flux from the Atlantic Ocean to inland.The amplified AEW activity, together with promoted moist convection and increased precipitation, results in a northern shift of the summer rainfall band during the mid-Holocene.

  • 36.
    Björck, Svante
    et al.
    Inst. för geo- och ekosystemvetenskaper Enheten för geologi, Lunds universitet.
    Moberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Historiska varningssignaler2010Ingår i: Sverige i nytt klimat - våtvarm utmaning / [ed] Birgitta Johansson, Stockholm: Forskningsrådet Formas , 2010, s. 71-86Kapitel i bok, del av antologi (Övrig (populärvetenskap, debatt, mm))
    Abstract [sv]

    De senaste tjugo årens klimat i Stockholmstrakten är troligen det varmaste under den senaste femhudraårsperioden. Människans utsläpp av växthusgaser har bidragit, men även naturliga faktorer. Av historien kan vi lära oss att klimatet plötsligt kan slå om till att fungera på ett helt nytt sätt - en förändring som kan bli en obehaglig överraskning för människans samhälle och dess känsliga infrastruktur. Därför bör vi vara lyhörda för varningssignaler från jordens klimatsystem. Varningssignaler är den geologiska historien full av, skriver Svante Björck och Anders Moberg.

  • 37. Björklund, Jesper
    et al.
    Seftigen, Kristina
    Stoffel, Markus
    Fonti, Marina V.
    Kottlow, Sven
    Frank, David C.
    Esper, Jan
    Fonti, Patrick
    Goosse, Hugues
    Grudd, Håkan
    Gunnarson, Björn E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Stockholms universitet, Naturvetenskapliga fakulteten, Bolincentret för klimatforskning (tills m KTH & SMHI).
    Nievergelt, Daniel
    Pellizzari, Elena
    Carrer, Marco
    von Arx, Georg
    Fennoscandian tree-ring anatomy shows a warmer modern than medieval climate2023Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 620, nr 7972, s. 97-103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Earth system models and various climate proxy sources indicate global warming is unprecedented during at least the Common Era. However, tree-ring proxies often estimate temperatures during the Medieval Climate Anomaly (950–1250 CE) that are similar to, or exceed, those recorded for the past century, in contrast to simulation experiments at regional scales. This not only calls into question the reliability of models and proxies but also contributes to uncertainty in future climate projections. Here we show that the current climate of the Fennoscandian Peninsula is substantially warmer than that of the medieval period. This highlights the dominant role of anthropogenic forcing in climate warming even at the regional scale, thereby reconciling inconsistencies between reconstructions and model simulations. We used an annually resolved 1,170-year-long tree-ring record that relies exclusively on tracheid anatomical measurements from Pinus sylvestris trees, providing high-fidelity measurements of instrumental temperature variability during the warm season. We therefore call for the construction of more such millennia-long records to further improve our understanding and reduce uncertainties around historical and future climate change at inter-regional and eventually global scales. 

  • 38.
    Blomqvist, Oskar
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statsvetenskapliga institutionen.
    Sambandet demokrati och klimatpåverkan:En fråga om ålder?2023Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Följande uppsats syftar tillatt undersöka huruvida det finns en villkorlig relation mellan demokrati och klimatpåverkan, där ålder spelar en avgörande roll för sambandetsexistens samtutfall. Frågeställningarna kring demokratis effekt på klimatpåverkanmed ålder i beaktning utgör en lucka i aktuellaforskningenoch är anledningen till attjust detta uppsatsämne valdes. Genom att undersöka dessa frågorså kan en bredare förståelseerhållasförpotentiellaorsak-och verkan sambandetmellan demokrati och klimatpåverkan, samtidigt som ålderns roll i detta fenomenstuderas. För att kunna undersöka dettaså genomförs dels en regressionsanalys, dels en interaktionsanalys, av 149 länders värden för olika variabler. Dessa variabler utgörs av index och data framtagna av erkända organisationer för det utvalda året 2021. I analysernaär Demokrati oberoendevariabeln, Koldioxidutsläpp per capita beroende variabeln och Demokrati interagerande med Andel Ungaär interaktionsvariabeln. Utöver dessa huvudvariabler så inkluderas ett antal kontrollvariablerockså,vars syftenär att stärka den interna validiteten, undvika urvalsfel samt tillgodose andra potentiella relationer.Tidigare forskning består av inkonsekventa ställningstagandetill sambandet mellan demokrati och klimatpåverkan. Uppsatsens finner ett positivt sambandmellan demokrati och koldioxidutsläpp per capitasom sedan övergår till ett negativt samband vid introduktionen av vissa kontrollvariabler. Utöver detta samband så finner uppsatsen ingetresultat som insinuerar existensen av en villkorlig relation mellan demokrati och klimatpåverkandärålder har någon inverkan påsambandets utfall. Således blir uppsatsen istället ett incitament för vidare forskning av dennavillkorliga relation.

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  • 39.
    Bogren, Fredrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Evidence for birch forests and a highly productive environment near the margin of the Fennoscandian ice sheet in the Värriötunturit area, northeastern Finland2019Självständigt arbete på avancerad nivå (masterexamen), 40 poäng / 60 hpStudentuppsats (Examensarbete)
    Abstract [en]

    High-resolution records of early Holocene deposits are rare, and as a consequence reconstruction of terrestrial environments very soon after the deglaciation has often been difficult. In this study the palaeoenvironmental conditions of early Holocene (c. 10600-7500 cal. yr BP) are reconstructed in the Värriötunturit area of northeastern Finland, using evidence from plant macrofossils and pollen preserved in a lake sediment sequence retrieved from the small lake Kuutsjärvi. Special emphasis is put on the environment immediately following the deglaciation as the base of the sediment sequence is rich in minerogenic material interpreted to have been deposited by meltwater pulses from the retreating ice sheet. The abundance and variety of fossil remains in these early meltwater deposits provide evidence for a very productive ice-marginal environment in the area between the lake and the ice sheet, and the presence of tree-type Betula macro remains as well as high percentage values of tree-type Betula pollen suggests that a subarctic birch forest established just a few years after the deglaciation. In the following centuries the birch forest around the lake became rich in an under growth of ferns, and at c. 9400 cal. yr BP a transition into a mixed pine and birch forest took place. Due to absence of indicator plant taxa in the sediment it was not possible to reconstruct temperature conditions for any parts of the sequence in this study. However, the rapid colonisation of birch forests suggests that the climate was warm already during deglaciation, which is also in accordance with climatic conditions reconstructed for the early Holocene in the nearby Sokli area just 10 km away, as well as in other parts of Fennoscandia and Russia.

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  • 40.
    Bourgeois, Quentin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Krejci, Radovan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment2015Ingår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, nr 16, s. 8411-8425Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Six years (200702012) of data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instrument were used to investigate the vertical distribution and transport of aerosols over the tropical South American continent and the southeast Pacific Ocean. The multiyear aerosol extinction assessment indicates that aerosols, mainly biomass burning particles emitted during the dry season in the Amazon Basin, are lifted in significant amounts over the Andes. The aerosols are mainly transported in the planetary boundary layer between the surface and 2 km altitude with an aerosol extinction maximum near the surface. During the transport toward the Andes, the aerosol extinction decreases at a rate of 0.02 km(-1) per kilometer of altitude likely due to dilution and deposition processes. Aerosols reaching the top of the Andes, at altitudes typically between 4 and 5 km, are entrained into the free troposphere (FT) over the southeast Pacific Ocean. A comparison between CALIOP observations and ERA-Interim reanalysis data indicates that during their long-range transport over the tropical Pacific Ocean, these aerosols are slowly transported toward the marine boundary layer by the large-scale subsidence at a rate of 0.4 cm s(-1). The observed vertical/horizontal transport ratio is 0.700.8 m km(-1) Continental aerosols linked to transport over the Andes can be traced on average over 4000 km away from the continent indicating an aerosol residence time of 809 days in the FT over the Pacific Ocean. The FT aerosol optical depth (AOD) above the Pacific Ocean near South American coast accounts on average for 6% and 25% of the total AOD during the season of low and high biomass burning, respectively. This result shows that, during the biomass burning season, continental aerosols largely influence the AOD over the remote southeast Pacific Ocean. Overall, FT AOD decrease exponentially with the distance to continental sources at a rate of about 10% per degree of longitude over the Pacific Ocean.

  • 41. Brandefelt, Jenny
    et al.
    Körnich, Heiner
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Northern Hemisphere stationary waves in future climate projections.2008Ingår i: Journal of Climate, Vol. 21, nr 23, s. 6341–6353-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The response of the atmospheric large-scale circulation to an enhanced greenhouse gas (GHG) forcing varies among coupled global climate model (CGCM) simulations. In this study, sixteen CGCM simulations of the response of the climate system to a 1% per year increase in the atmospheric CO2 concentration to quadrupling are analysed with focus on Northern Hemisphere winter. A common signal in fourteen out of sixteen simulations is an increased or unchanged stationary wave amplitude. A majority of the simulations may be categorised into one of three groups based on the GHG induced changes in the atmospheric stationary waves. The response of the zonal mean barotropic wind is similar within each group. 50% of the simulations belong to the first group which is categorised by a stationary wave with five waves encompassing the whole NH and a strengthening of the zonal mean barotropic wind. The second and third group, consisting of three and two simulations respectively, are characterised by a broadening and a northward shift of the zonal mean barotropic wind respectively. A linear model of barotropic vorticity is employed to study the importance of these mean flow changes to the stationary wave response. The linear calculations indicate that the GHG induced mean wind changes explain 50%, 4% and 37% of the stationary wave changes in each group respectively. Thus, for the majority of simulations the zonal mean wind changes do significantly explain the stationary wave response.

  • 42.
    Bring, Arvid
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Arctic Climate and Water Change: Information Relevance for Assessment and Adaptation2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The Arctic is subject to growing economic and political interest. Meanwhile, its water and climate systems are in rapid transformation. Relevant and accessible information about water and climate is therefore vital to detect, understand and adapt to the changes. This thesis investigates hydrological monitoring systems, climate model data, and our understanding of hydro-climatic change, for adaptation to water system changes in the Arctic. Results indicate a lack of harmonized water chemistry data, which may impede efforts to understand transport and origin of key waterborne constituents. Further development of monitoring cannot rely only on a reconciliation of observations and projections on where climate change will be the most severe, as they diverge in this regard. Climate model simulations of drainage basin temperature and precipitation have improved between two recent model generations, but large inaccuracies remain for precipitation projections. Late 20th-century discharge changes in major Arctic rivers generally show excess of water relative to precipitation changes. This indicates a possible contribution of stored water from permafrost or groundwater to sea level rise. The river contribution to the increasing Arctic Ocean freshwater inflow matches that of glaciers, which underlines the importance of considering all sources when assessing change. To provide adequate information for research and policy, Arctic hydrological and hydrochemical monitoring needs to be extended, better integrated and made more accessible. This especially applies to hydrochemistry monitoring, where a more complete set of monitored basins is motivated, including a general extension for the large unmonitored areas close to the Arctic Ocean. Improvements in climate model parameterizations are needed, in particular for precipitation projections. Finally, further water-focused data and modeling efforts are required to resolve the source of excess discharge in Arctic rivers.

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  • 43.
    Bring, Arvid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Divergent prioritization relevance of Arctic hydrological monitoring under climate change2012Konferensbidrag (Övrigt vetenskapligt)
  • 44.
    Bring, Arvid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Divergent relevance and prioritization basis for hydro-climatic change monitoring in the Arctic2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Climate change affects society and the Earth System largely through water cycle changes, such as altered precipitation patterns and increased drought and flood pressures. In the Arctic, which undergoes a particularly large and rapid environmental transformation, information on water cycle changes is crucial to plan for societal adaptation. A prioritization strategy is then needed for how (where and when) monitoring should be focused to get the most relevant information and data on Arctic hydro-climatic change with limited available resources. We investigate different possible strategies for a geographic prioritization of hydro-climatic change monitoring in the Arctic. Results show conflicting prioritization basis across 14 major Arctic hydrological basins. The current monitoring density distribution is relevant for the so far observed but not for the projected future changes in Arctic climate. The present and the projected future hot-spots of greatest climate change differ, so that major spatial shifts must be anticipated in the future with regard to climate change severity across the Arctic. Important temporal shifts must further be anticipated in several major Arctic basins with currently decreasing but expected future increasing precipitation.

  • 45.
    Bring, Arvid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Evaluation of IPCC AR4 climate model performance over 14 major Arctic watershedsManuskript (preprint) (Övrigt vetenskapligt)
  • 46.
    Bring, Arvid
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Destouni, Georgia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Hydro-climatic change indications of Arctic permafrost thawing2012Konferensbidrag (Refereegranskat)
  • 47.
    Brodeau, Laurent
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Koenigk, Torben
    Extinction of the northern oceanic deep convection in an ensemble of climate model simulations of the 20th and 21st centuries2016Ingår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 46, nr 9, s. 2863-2882Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the variability and the evolution of oceanic deep convection in the northern North Atlantic and the Nordic Seas from 1850 to 2100 using an ensemble of 12 climate model simulations with EC-Earth. During the historical period, the model shows a realistic localization of the main sites of deep convection, with the Labrador Sea accounting for most of the deep convective mixing in the northern hemisphere. Labrador convection is partly driven by the NAO (correlation of 0.6) and controls part of the variability of the AMOC at the decadal time scale (correlation of 0.6 when convection leads by 3-4 years). Deep convective activity in the Labrador Sea starts to decline and to become shallower in the beginning of the twentieth century.  The decline is primarily caused by a decrease of the sensible heat loss to the atmosphere in winter resulting from increasingly warm atmospheric conditions. It occurs stepwise and is mainly the consequence of two severe drops in deep convective activity during the 1920s and the 1990s.  These two events can both be linked to the low-frequency variability of the NAO. A warming of the sub-surface, resulting from reduced convective mixing, combines with an increasing influx of freshwater from the Nordic Seas to rapidly strengthen the surface stratification and prevent any possible resurgence of deep convection in the Labrador Sea after the 2020s. Deep convection in the Greenland Sea starts to decline in the 2020s, until complete extinction in 2100. As a response to the extinction of deep convection in the Labrador and Greenland Seas, the AMOC undergoes a linear decline at a rate of about -0.3 Sv per decade during the twenty-first century.

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  • 48.
    Broomé, Sara
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Stockholm University.
    Atlantic Water in the Nordic Seas: A satellite altimetry perspective on ocean circulation2020Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The Atlantic Water in the Nordic Seas contributes to the mild climate of Northern Europe and is the main oceanic source of heat for the Arctic. The northward bound transport of the warm and saline Atlantic Water is mediated by a topographically constrained cyclonic boundary current along the Norwegian continental slope. The analysis within this thesis is based on satellite observations of dynamic Sea Surface Heights (SSH) from 1993 to the recent present, combined with both hydrographic observations and modelling. It provides some new perspectives and results, as well as corroborates the essential role of bottom topography for the circulation in the Nordic Seas.

    In the first part of the thesis, the topographic constraint is used in the analysis by examining the satellite-derived SSH along topographic contours. We find stationary along-contour anomalies that indicate deviations from strict topographic steering. However, we show that these deviations are dynamically consistent with, and can be explained by, potential vorticity conservation in an adiabatic steady-state model for flow over a topographic slope. The analysis along topographic contours is further developed to study northward-propagating, low-frequency ocean temperature signals. These signals have an expression in the SSH and their propagation speed is remarkably slow compared to the current speed. We propose a conceptual model of shear dispersion effects, in which the effective advection speed of a tracer is determined not only by the rapid current core, but by a mean velocity taken over the cross-flow extent of Atlantic Water. The model predicts a reduced effective tracer advection velocity, comparable to the one observed.

    The close connection between anomalies in SSH and heat content is further used to study decadal variability in the Nordic Seas. There is a shift in decadal trends in the mid-2000s, from a period of strong increase in SSH and heat content to a more stagnant period. We find this variability to be forced remotely, rather than by local air-sea heat fluxes. By developing a conceptual model of ocean heat convergence, we are able to explain the broad features of the decadal changes with the temperature variability of the inflowing Atlantic Water from the subpolar North Atlantic.

    In the final part of the thesis, satellite-derived surface geostrophic velocity fields are used as input to a Lagrangian trajectory model. Based on this, we study the fractionation of the Atlantic Water in the Nordic Seas between the two straits towards the Arctic Ocean: the Barents Sea Opening and the Fram Strait. This Lagrangian approach also provides insights on the origin of the water that reach the straits. We find that it is the frontal current branch, rather than the slope current, that contributes to the variability of the Barents Sea Opening inflow of warm Atlantic Water, and thus potentially to the climate of the Barents Sea and its sea ice cover.

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    Atlantic Water in the Nordic Seas: A satellite altimetry perspective on ocean circulation
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  • 49.
    Broomé, Sara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Chafik, Léon
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Nilsson, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Mechanisms of decadal changes in sea surface height and heat content in the eastern Nordic Seas2020Ingår i: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 16, nr 3, s. 715-728Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Nordic Seas constitute the main ocean conveyor of heat between the North Atlantic Ocean and the Arctic Ocean. Although the decadal variability in the subpolar North Atlantic has been given significant attention lately, especially regarding the cooling trend since the mid-2000s, less is known about the potential connection downstream in the northern basins. Using sea surface heights from satellite altimetry over the past 25 years (1993–2017), we find significant variability on multiyear to decadal timescales in the Nordic Seas. In particular, the regional trends in sea surface height show signs of a weakening since the mid-2000s, as compared to the rapid increase in the preceding decade since the early 1990s. This change is most prominent in the Atlantic origin waters in the eastern Nordic Seas and is closely linked, as estimated from hydrography, to heat content. Furthermore, we formulate a simple heat budget for the eastern Nordic Seas to discuss the relative importance of local and remote sources of variability; advection of temperature anomalies in the Atlantic inflow is found to be the main mechanism. A conceptual model of ocean heat convergence, with only upstream temperature measurements at the inflow to the Nordic Seas as input, is able to reproduce key aspects of the decadal variability in the heat content of the Nordic Seas. Based on these results, we argue that there is a strong connection with the upstream subpolar North Atlantic. However, although the shift in trends in the mid-2000s is coincident in the Nordic Seas and the subpolar North Atlantic, the eastern Nordic Seas have not seen a reversal of trends but instead maintain elevated sea surface heights and heat content in the recent decade considered here.

  • 50. Brugnara, Y.
    et al.
    Auchmann, R.
    Brönnimann, S.
    Allan, R. J.
    Auer, I.
    Barriendos, M.
    Bergström, H.
    Bhend, J.
    Brázdil, R.
    Compo, G. P.
    Cornes, R. C.
    Dominguez-Castro, F.
    van Engelen, A. F. V.
    Filipiak, J.
    Holopainen, J.
    Jourdain, S.
    Kunz, M.
    Luterbacher, J.
    Maugeri, M.
    Mercalli, L.
    Moberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Mock, C. J.
    Pichard, G.
    Řezníčková, L.
    van der Schrier, G.
    Slonosky, V.
    Ustrnul, Z.
    Valente, M. A.
    Wypych, A.
    Yin, X.
    A collection of sub-daily pressure and temperature observations for the early instrumental period with a focus on the "year without a summer" 18162015Ingår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 11, nr 8, s. 1027-1047Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It is associated with a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years of and immediately following the eruption (1815–1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than 50 sub-daily series from land observatories in Europe and North America and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level. Moreover, an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected data set, the variance in the pressure observations is compared with modern climatologies, and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank.

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