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  • 1.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Anthropogenic influence on climate through changes in aerosol emissions from air pollution and land use change2017Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 2.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Historical anthropogenic radiative forcing of changes in biogenic secondary organic aerosol2015Licentiate thesis, comprehensive summary (Other academic)
    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.

  • 3.
    Ahmed, Moinuddin
    et al.
    Fed Urdu Univ Arts Sci & Technol, Dept Bot, Karachi 75300, Pakistan.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Zorita, Eduardo
    PAGES 2k Consortium,
    Continental-scale temperature variability during the past two millennia2013In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 6, no 5, p. 339-346Article in journal (Refereed)
    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.

  • 4.
    Ampel, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (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 glacialperiod2010In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 44, no 2, p. 397-404Article in journal (Refereed)
    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.

  • 5.
    Asokan, Shilpa M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Appendix to Paper V: Climate model performance versus basin-scalehydro-climatic dataManuscript (preprint) (Other academic)
  • 6.
    Asokan, Shilpa M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Irrigation effects on hydro-climatic change: Basin-wise water balance-constrained quantification and cross-regional comparison2014In: Surveys in geophysics, ISSN 0169-3298, E-ISSN 1573-0956, Vol. 35, no 3, p. 879-895Article in journal (Refereed)
    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.

  • 7.
    Asokan, Shilpa M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Dutta, Dushmanta
    Analysis of water resources in the Mahanadi River Basin, India under projected climate conditions2008In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 22, no 18, p. 3589-3603Article in journal (Refereed)
    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.

  • 8.
    Asokan, Shilpa M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jarsjö, Jerker
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Vapor flux by evapotranspiration: effects of changes in climate, land-use and water-use2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no D24Article in journal (Refereed)
    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.

  • 9. Asselt, Harro van
    et al.
    Mehling, Michael E.
    Siebert, Clarisse Kehler
    Stockholm University, Stockholm Environment Institute.
    The Changing Architecture of International Climate Change Law2015In: Research Handbook on Climate Change Mitigation Law / [ed] G. van Calster et al., Cheltenham: Edward Elgar Publishing, 2015, p. Ch. 2-Chapter in book (Refereed)
  • 10.
    Asselt, Harro van
    et al.
    Stockholm University, Stockholm Environment Institute.
    Zelli, Fariborz
    Lund University.
    Connect the dots: Managing the fragmentation of global climate governance2014In: Environmental Economics and Policy Studies, ISSN 1432-847X, E-ISSN 1867-383X, Vol. 16, no 2, p. 137-155Article in journal (Refereed)
    Abstract [en]

    The debate about post-2012 global climate governance has been framed largely by proponents and opponents of the policymaking process established by the United Nations Framework Convention on Climate Change (UNFCCC). In light of the proliferation of institutions governing some aspects of climate change, analysts have asked whether a centralized or a polycentric climate governance architecture will be more effective, efficient, equitable, or viable. While these are valid questions, they obscure the fact that global climate governance is already polycentric, or rather: fragmented. This article argues that the more pertinent questions are how to sensibly link the different elements of global climate governance, and what the role of the UNFCCC could be in this regard. We examine these two questions for three aspects of global climate governance: international climate technology initiatives, emerging emissions trading systems, and unilateral trade measures. The article shows that there are strong arguments for coordination in all of these cases, and illustrates the possible role of the UNFCCC. It concludes, however, that possibilities for coordination will eventually be limited by underlying tensions that will plague any future climate governance architecture.

  • 11.
    Axelsson, Pia
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Minskad trädtillväxt under Lilla sitiden?: En dendroklimatologisk jämförelse mellan nutid och 1600-talet invid trädgränsen i norra Skandinavien2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    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. 

  • 12. Azcárate, Juan
    et al.
    Balfors, Berit
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bring, Arvid
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Transboundary approach proposal for sustainable and climate change adaptation strategies in the Arctic2012Conference paper (Other academic)
  • 13.
    Barrientos, Natalia
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Arctic Ocean benthic foraminifera preservation and Mg/Ca ratios: Implications for bottom water palaeothermometry2018Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 14.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Coxall, Helen
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lear, Caroline
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Muschitiello, Francesco
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas
    Semiletov, Igor
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Late Holocene variability in Arctic Ocean Pacific Water inflow through the Bering StraitManuscript (preprint) (Other academic)
  • 15.
    Barrientos, Natalia
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Lear, Caroline H.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Stranne, Christian
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Cronin, Thomas M.
    Gukov, Aleksandr Y.
    Coxall, Helen K.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Arctic Ocean benthic foraminifera Mg/Ca ratios and global Mg/Ca-temperature calibrations: New constraints at low temperaturesIn: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533Article in journal (Refereed)
    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.

  • 16. Benze, Susanne
    et al.
    Randall, Cora E.
    Karlsson, Bodil
    Stockholm University, Faculty of Science, Department of Meteorology .
    Harvey, V. Lynn
    DeLand, Matthew T.
    Thomas, Gary E.
    Shettle, Eric P.
    On the onset of polar mesospheric cloud seasons as observed by SBUV2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. D07104-Article in journal (Refereed)
    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.

  • 17.
    Benzie, Magnus
    et al.
    Stockholm University, Stockholm Environment Institute.
    Wallgren, Oskar
    Stockholm University, Stockholm Environment Institute.
    Initiating and sustaining adaptation in the private sector2014In: Climate change adaptation manual: lessons learned from European and other industrialized countries / [ed] Andrea Prutsch, Torsten Grothmann, Sabine McCallum, Inke Schauser, Rob Swart, London: Routledge, 2014, p. 78-84Chapter in book (Refereed)
  • 18. Bisaro, Alexander
    et al.
    Hinkel, Jochen
    Davis, Marion
    Stockholm University, Stockholm Environment Institute.
    Klein, Richard J.T.
    Stockholm University, Stockholm Environment Institute.
    Supporting NAP development with the PROVIA Guidance: A user companion2014Report (Other academic)
    Abstract [en]

    This brochure explains how the PROVIA Guidance on Assessing Vulnerability, Impacts and Adaptation to Climate Change can be used to better understand key concepts and available methods and tools throughout the National Adaptation Plan process.

  • 19.
    Björck, Svante
    et al.
    Inst. för geo- och ekosystemvetenskaper Enheten för geologi, Lunds universitet.
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Historiska varningssignaler2010In: Sverige i nytt klimat - våtvarm utmaning / [ed] Birgitta Johansson, Stockholm: Forskningsrådet Formas , 2010, p. 71-86Chapter in book (Other (popular science, discussion, etc.))
    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.

  • 20.
    Bourgeois, Quentin
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 16, p. 8411-8425Article in journal (Refereed)
    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.

  • 21. Brandefelt, Jenny
    et al.
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology.
    Northern Hemisphere stationary waves in future climate projections.2008In: Journal of Climate, Vol. 21, no 23, p. 6341–6353-Article in journal (Refereed)
    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.

  • 22.
    Bring, Arvid
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Arctic Climate and Water Change: Information Relevance for Assessment and Adaptation2013Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 23.
    Bring, Arvid
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Divergent prioritization relevance of Arctic hydrological monitoring under climate change2012Conference paper (Other academic)
  • 24.
    Bring, Arvid
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Divergent relevance and prioritization basis for hydro-climatic change monitoring in the Arctic2012Conference paper (Refereed)
    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.

  • 25.
    Bring, Arvid
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Evaluation of IPCC AR4 climate model performance over 14 major Arctic watershedsManuscript (preprint) (Other academic)
  • 26.
    Bring, Arvid
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hydro-climatic change indications of Arctic permafrost thawing2012Conference paper (Refereed)
  • 27.
    Brodeau, Laurent
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Koenigk, Torben
    Extinction of the northern oceanic deep convection in an ensemble of climate model simulations of the 20th and 21st centuries2016In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 46, no 9, p. 2863-2882Article in journal (Refereed)
    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.

  • 28. Brown, S.
    et al.
    Nicholls, R.J.
    Hanson, S.
    Brundrit, G.
    Klein, Richard J.T.
    Stockholm University, Stockholm Environment Institute. Centre for Climate Science and Policy Research, Linköping University.
    Shifting perspectives on coastal impacts and adaptation2014In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 4, no 9, p. 752-755Article in journal (Refereed)
  • 29. 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
    Stockholm University, Faculty of Science, Department of Physical Geography.
    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" 18162015In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 11, no 8, p. 1027-1047Article in journal (Refereed)
    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.

  • 30. Brunet, Manola
    et al.
    Jones, Philip D.
    Sigró, Javier
    Saladié, Oscar
    Aguilar, Enric
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Della-Marta, Paul M.
    Lister, David
    Walther, Alexander
    López, Diego
    Temporal and spatial temperature variability and change over Spain during 1850-20052007In: Journal of Gephysical Research: Atmospheres, Vol. 112, no D12117Article in journal (Refereed)
    Abstract [en]

    We analyze temporal and spatial patterns of temperature change over Spain during the period 1850–2005, using daily maximum (T max), minimum (T min), and mean (T mean) temperatures from the 22 longest and most reliable Spanish records. Over mainland Spain, a significant (at 0.01 level) warming of 0.10°C/decade is found for the annual average of T mean. Autumn and winter contributed slightly more than spring and summer to the annual warming over the 1850–2005 period. The overall warming is also associated with higher rates of change for T max than T min (0.11° versus 0.08°C/decade for 1850–2005). This asymmetric diurnal warming increased in the twentieth century (0.17° versus 0.09°C/decade during 1901–2005). Nevertheless, at many (few) individual stations, the difference between T max and T min is not statistically significant over 1850–2005 (1901–2005). Principal Component Analysis has been carried out to identify spatial modes of Spanish long-term temperature variability (1901–2005). Three principal spatial patterns are found, Northern Spain, Southeastern and Eastern Spain, and Southwestern Spain. All three patterns show similar significant warming trends. The overall warming has been more associated with reductions in cold extremes, as opposed to increases in warm extremes. Estimated trends in the number of moderately extreme cold days (T max < 10th percentile) and moderately extreme cold nights (T min < 10th percentile) show significant reductions of 0.74 and 0.54 days/decade, respectively, over 1850–2005. Moderately extreme warm days and nights (T max and T min > 90th percentile) increased significantly but at lower rates of 0.53 and 0.49 days/decade.

  • 31. Brunet, Manola
    et al.
    Saladié, Oscar
    Jones, Phil
    Sigró, Javier
    Aguilar, Enric
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lister, David
    Walther, Alexander
    Almarza, Carlos
    A case-study/guidance on the development of long-term daily adjusted temperature datasets: Climate Data and Monitoring WCDMP-No. 662008Report (Other academic)
  • 32. Brunet, Manola
    et al.
    Sigró, Javier
    Jones, Philip D.
    Saladié, Oscar
    Aguilar, Enric
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lister, David
    Walther, Alexander
    Long-term changes in extreme temperatures and precipitation in Spain2007In: Contributions to Science: The International Journal of the Institute for Catalan Studies (IEC), ISSN 1575-6343, Vol. 3, no 3, p. 331-342Article in journal (Other academic)
    Abstract [en]

    The development of the Spanish daily adjusted temperature

    series (SDATS) and the Spanish daily adjusted precipitation series

    (SDAPS) datasets in the framework of the European Community

    (EC)-funded project EMULATE (European and North Atlantic

    daily to MULtidecadal climATE variability) enabled the

    assessment of long-term annual changes of extreme temperature

    and precipitation indices over peninsular Spain for the period

    1901–2005. Within this framework, a set of procedures

    was developed to generate long-term (1850–2005) daily adjusted

    temperature and precipitation series and to use them to

    assess changes in climatic extremes. The present report describes

    details of the data employed to analyze the behavior of

    Spanish climate extremes and discusses the results of investigations

    into the annual changes in selected indices that occurred

    during the 20th century: exceedances of upper and lower

    percentiles of daily maximum (Tmax) and minimum (Tmin)

    temperatures, cold-spell duration index (CSDI), warm-spell duration

    index (WSDI), daily rainfall (R) exceeding the 95th and 99th

    percentiles, simple daily intensity index (SDII), and greatest 1–

    and 5-day total precipitation. Upper and lower temperature

    percentiles increased during the 20th century over mainland

    Spain, but changes in daytime extreme temperatures were

    larger than the changes in night-time extreme temperatures.

    This pattern, however, shifted slightly in the recent period of

    strong warming, with more similar rates of change among daytime

    and night-time extreme temperatures. Changes in extreme

    precipitation indices were not as evident as those in extreme-

    temperature indices, but there was a tendency towards

    heavier precipitation.

  • 33. Brázdil, Rudolf
    et al.
    Dobrovolný, Petr
    Luterbacher, Jürg
    Moberg, Anders
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Pfister, Christian
    Wheeler, Dennis
    Zorita, Eduardo
    European climate of the past 500 years: new challenges for historical climatology2010In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 101, no 1-2, p. 7-40Article in journal (Refereed)
    Abstract [en]

    Temperature reconstructions from Europe for the past 500 years basedon documentary and instrumental data are analysed. First, the basic documentarydata sources, including information about climate and weather-related extremes, aredescribed. Then, the standard palaeoclimatological reconstruction method adoptedhere is discussed with a particular application to temperature reconstructions fromdocumentary-based proxy data. The focus is on two new reconstructions; January–April mean temperatures for Stockholm (1502–2008), based on a combination ofdata for the sailing season in the Stockholm harbour and instrumental temperaturemeasurements, and monthly Central European temperature (CEuT) series (1500–2007) based on documentary-derived temperature indices of the Czech Republic,Germany and Switzerland combined with instrumental records from the samecountries. The two series, both of which are individually discussed in greater detail in subsequent papers in this special edition, are here compared and analysed usingrunning correlations and wavelet analysis. While the Stockholm series shows apronounced low-frequency component, the CEuT series indicates much weaker lowfrequencyvariations. Both series are analysed with respect to three different longperiodreconstructions of the North Atlantic Oscillation (NAO) and are comparedwith other European temperature reconstructions based on tree-rings, wine-harvestdata and various climate multiproxies. Correlation coefficients between individualproxy-based series show weaker correlations compared to the instrumental data.There are also indications of temporally varying temperature cross-correlationsbetween different areas of Europe. The two temperature reconstructions have alsobeen compared to geographically corresponding temperature output from simulationswith global and regional climate models for the past few centuries. The findingsare twofold: on the one hand, the analysis reinforces the hypothesis that the indexdatabased CEuT reconstruction may not appropriately reflect the centennial scalevariations. On the other hand, it is possible that climate models may underestimateregional decadal variability. By way of a conclusion, the results are discussed froma broader point of view and attention is drawn to some new challenges for futureinvestigations in the historical climatology in Europe.

  • 34.
    Bröder, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Tesi, Tommaso
    Semiletov, Igor P.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    The integrated flux of terrigenous organic carbon degradation in surface sediments on the Laptev and East Siberian Sea ShelvesManuscript (preprint) (Other academic)
  • 35.
    Bröder, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Tesi, Tommaso
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor P.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Bounding cross-shelf transport time and degradation in land-ocean carbon transferArticle in journal (Refereed)
  • 36. Burton, Ian
    et al.
    Dube, O. Pauline
    Campbell-Lendrum, Diarmid
    Klein, Richard J.T.
    Stockholm University, Stockholm Resilience Centre, Stockholm Environment Institute.
    Kehler Siebert, Clarisse
    Stockholm University, Stockholm Resilience Centre, Stockholm Environment Institute.
    Managing the risks: international level and integration across scales2012In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation: Special Report of the Intergovernmental Panel on Climate Change / [ed] Christopher B. Field et al., Cambridge University Press, 2012, p. 393-435Chapter in book (Other academic)
  • 37. Büntgen, Ulf
    et al.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Esper, Jan
    Luterbacher, Jürg
    Wagner, Sebastian
    Werner, Johannes P.
    Consolidation, finalization and publication of the Euro-Med2k database2016In: Past Global Changes Magazine, ISSN 2411-9180, Vol. 24, no 1, p. 43-43Article in journal (Other academic)
  • 38. Büntgen, Ulf
    et al.
    Luterbacher, Jürg
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Esper, Jan
    Fleitmann, Dominik
    Gagen, Mary
    González-Rouco, Fidel
    Wagner, Sebastian
    Werner, Johannes
    Zorita, Eduardo
    Martínez Peña, Fernando
    Towards a spatiotemporal expansion of temperature and hydroclimatic proxy archives2015In: Past Global Changes Magazine, ISSN 2411-605X, Vol. 23, no 1, p. 34-34Article in journal (Other academic)
  • 39. Büntgen, Ulf
    et al.
    Trnka, Miroslav
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kyncl, Tomáš
    Kyncl, Josef
    Luterbacher, Jürg
    Zorita, Eduardo
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Auer, Ingeborg
    Konter, Oliver
    Schneider, Lea
    Tegel, Willy
    Štěpánek, Petr
    Brönnimann, Stefan
    Hellmann, Lena
    Nievergelt, Daniel
    Esper, Jan
    Tree-Ring Amplification of the Early Nineteenth-Century Summer Cooling in Central Europe2015In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 28, no 13, p. 5272-5288Article in journal (Refereed)
    Abstract [en]

    Annually resolved and absolutely dated tree-ring chronologies are the most important proxy archives to reconstruct climate variability over centuries to millennia. However, the suitability of tree-ring chronologies to reflect the “true” spectral properties of past changes in temperature and hydroclimate has recently been debated. At issue is the accurate quantification of temperature differences between early nineteenth-century cooling and recent warming. In this regard, central Europe (CEU) offers the unique opportunity to compare evidence from instrumental measurements, paleomodel simulations, and proxy reconstructions covering both the exceptionally hot summer of 2003 and the year without summer in 1816. This study uses 565 Swiss stone pine (Pinus cembra) ring width samples from high-elevation sites in the Slovakian Tatra Mountains and Austrian Alps to reconstruct CEU summer temperatures over the past three centuries. This new temperature history is compared to different sets of instrumental measurements and state-of-the-art climate model simulations. All records independently reveal the coolest conditions in the 1810s and warmest after 1996, but the ring width–based reconstruction overestimates the intensity and duration of the early nineteenth-century summer cooling by approximately 1.5°C at decadal scales. This proxy-specific deviation is most likely triggered by inflated biological memory in response to reduced warm season temperature, together with changes in radiation and precipitation following the Tambora eruption in April 1815. While suggesting there exists a specific limitation in ring width chronologies to capture abrupt climate perturbations with increased climate system inertia, the results underline the importance of alternative dendrochronological and wood anatomical parameters, including stable isotopes and maximum density, to assess the frequency and severity of climatic extremes.

  • 40.
    Caballero, Rodrigo
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Lynch, Peter
    University College Dublin.
    Climate modelling and deep-time climate change.2011In: Climate Change, Ecology and Systematics., Cambridge University Press, 2011Chapter in book (Refereed)
  • 41. Campell, R
    et al.
    Robertson, I
    McCarrol, D
    Loader, NJ
    Grudd, H
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Gunnarson, B
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Calibration proxy-climate relationshis in central Sweden using stable isotopes in tree rings.2008Conference paper (Other academic)
  • 42.
    Carlson, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Vegetation sensitivity to alternative warming scenarios for the early EoceneManuscript (preprint) (Other academic)
  • 43. Carstensen, Jacob
    et al.
    Andersen, Jesper H.
    Gustafsson, Bo G.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Conley, Daniel J.
    Deoxygenation of the Baltic Sea during the last century2014In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, no 15, p. 5628-5633Article in journal (Refereed)
    Abstract [en]

    Deoxygenation is a global problem in coastal and open regions of the ocean, and has led to expanding areas of oxygen minimum zones and coastal hypoxia. The recent expansion of hypoxia in coastal ecosystems has been primarily attributed to global warming and enhanced nutrient input from land and atmosphere. The largest anthropogenically induced hypoxic area in the world is the Baltic Sea, where the relative importance of physical forcing versus eutrophication is still debated. We have analyzed water column oxygen and salinity profiles to reconstruct oxygen and stratification conditions over the last 115 y and compare the influence of both climate and anthropogenic forcing on hypoxia. We report a 10-fold increase of hypoxia in the Baltic Sea and show that this is primarily linked to increased inputs of nutrients from land, although increased respiration from higher temperatures during the last two decades has contributed to worsening oxygen conditions. Although shifts in climate and physical circulation are important factors modulating the extent of hypoxia, further nutrient reductions in the Baltic Sea will be necessary to reduce the ecosystems impacts of deoxygenation.

  • 44.
    Chabangborn, Akkaneewut
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Asian monsoon over mainland Southeast Asia in the past 25 000 years2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The objective of this research is to interpret high-resolution palaeo-proxy data sets to understand the Asian summer monsoon variability in the past. This was done by synthesizing published palaeo-records from the Asian monsoon region, model simulation comparisons, and analysing new lake sedimentary records from northeast Thailand.

    Palaeo-records and climate modeling indicate a strengthened summer monsoon over Mainland Southeast Asia during the Last Glacial Maximum (LGM), compared to dry conditions in other parts of the Asian monsoon region. This can be explained by the LGM sea level low stand, which exposed Sundaland and created a large land-sea thermal contrast. Sea level rise ~19 600 years before present (BP), reorganized the atmospheric circulation in the Pacific Ocean and weakened the summer monsoon between 20 000 and 19 000 years BP.

    Both the Mainland Southeast Asia and the East Asian monsoon hydroclimatic records point to an earlier Holocene onset of strengthened summer monsoon, compared to the Indian Ocean monsoon. The asynchronous evolution of the summer monsoon and a time lag of 1500 years between the East Asian and the Indian Ocean monsoon can be explained by the palaeogeography of Mainland Southeast Asia, which acted as a land bridge for the movement of the Intertropical Convergence Zone.

    The palaeo-proxy records from Lake Kumphawapi compare well to the other data sets and suggest a strengthened summer monsoon between 10 000 and 7000 years BP and a weakening of the summer monsoon thereafter. The data from Lake Pa Kho provides a picture of summer monsoon variability over 2000 years. A strengthened summer monsoon prevailed between BC 170-AD 370, AD 800-960 and since AD 1450, and was weaker about AD 370-800 and AD 1300-1450. The movement of the mean position of the Intertropical Convergence Zone explains shifts in summer monsoon intensity, but weakening of the summer monsoon between 960 and 1450 AD could be affected by changes in the Walker circulation.

  • 45.
    Chabangborn, Akkaneewut
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Brandefelt, Jenny
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Asian monsoon climate during the Last Glacial Maximum: palaeo-data–model comparisons2013In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 43, no 1, p. 220-242Article in journal (Refereed)
    Abstract [en]

    The Last Glacial Maximum (LGM) (23-19ka BP) in the Asian monsoon region is generally described as cool and dry, due to a strong winter monsoon. More recently, however, palaeo-data and climate model simulations have argued for a more variable LGM Asian monsoon climate with distinct regional differences. We compiled, evaluated, and partly re-assessed proxy records for the Asian monsoon region in terms of wet/dry climatic conditions based on precipitation and effective moisture, and of sea surface temperatures. The comparison of the palaeo-data set to LGM simulations by the Climate Community System Model version 3 (CCSM3) shows fairly good agreement: a dry LGM climate in the western and northern part due to a strengthened winter monsoon and/or strengthened westerly winds and wetter conditions in equatorial areas, due to a stronger summer monsoon. Data-model discrepancies are seen in some areas and are ascribed to the fairly coarse resolution of CCSM3 and/or to uncertainties in the reconstructions. Differences are also observed between the reconstructed and simulated northern boundaries of the Intertropical Convergence Zone (ITCZ). The reconstructions estimate a more southern position over southern India and the Bay of Bengal, whereas CCSM3 simulates a more northern position. In Indochina, the opposite is the case. The palaeo-data indicate that climatic conditions changed around 20-19ka BP, with some regions receiving higher precipitation and some experiencing drier conditions, which would imply a distinct shift in summer monsoon intensity. This shift was probably triggered by the late LGM sea-level rise, which led to changes in atmosphere-ocean interactions in the Indian Ocean. The overall good correspondence between reconstructions and CCSM3 suggests that CCSM3 simulates LGM climate conditions over subtropical and tropical areas fairly well. The few high-resolution qualitative and quantitative palaeo-records available for the large Asian monsoon region make reconstructions however still uncertain

  • 46.
    Chabangborn, Akkaneewut
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Climate over mainland Southeast Asia 10.5–5 ka2014In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 29, no 5, p. 445-454Article in journal (Refereed)
    Abstract [en]

    We assembled and evaluated Holocene palaeo-vegetation records regarding semi-quantitative precipitation and temperature for mainland Southeast Asia and compared these with precipitation reconstructions for the Indian Ocean (IOM) and East Asian (EAM) monsoon sub-systems. Our results indicate that temperatures and precipitation in mainland Southeast Asia generally exceeded 18 °C and 1100 mm a−1 during the Holocene. Mainland Southeast Asia experienced cool/wet climatic conditions between 10.5 and 10 ka BP, a warmer/drier climate between 10 and 9 ka BP, cooler/wetter conditions between 9 and 7 ka BP, and moderately warmer/drier conditions since 7 ka BP. The reconstructed summer monsoon intensity compares well with the reconstructed hydroclimate for the EAM region, but diverges from that of the IOM region between 10.5 and 9 ka BP and 7–6.5 ka BP. This discrepancy is explained by differences in land–sea configuration, and regional sea-level history. A strengthening/weakening of the Asian summer monsoon between 9 and 7 ka BP and after 6.5 ka BP, respectively, is observed across the whole Asian monsoon region. Our new data sets support an asynchronous onset of the Asian summer monsoon optimum.

  • 47.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History. Stockholm University, Faculty of Humanities, Centre for Medieval Studies.
    A new reconstruction of temperature variability in the extra-tropical Northern Hemisphere during the last two millennia2010In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 92A, no 3, p. 339-351Article in journal (Refereed)
    Abstract [en]

    A new temperature reconstruction with decadal resolution, covering the last two millennia, is presented for the extra-tropical Northern Hemisphere (90–30°N), utilizing many palaeotemperature proxy records never previously included in any large-scale temperature reconstruction. The amplitude of the reconstructed temperature variability on centennial time-scales exceeds 0.6°C. This reconstruction is the first to show a distinct Roman Warm Period c. AD 1–300, reaching up to the 1961–1990 mean temperature level, followed by the Dark Age Cold Period c. AD 300–800. The Medieval Warm Period is seen c. AD 800–1300 and the Little Ice Age is clearly visible c. AD 1300–1900, followed by a rapid temperature increase in the twentieth century. The highest average temperatures in the reconstruction are encountered in the mid to late tenth century and the lowest in the late seventeenth century. Decadal mean temperatures seem to have reached or exceeded the 1961–1990 mean temperature level during substantial parts of the Roman Warm Period and the Medieval Warm Period. The temperature of the last two decades, however, is possibly higher than during any previous time in the past two millennia, although this is only seen in the instrumental temperature data and not in the multi-proxy reconstruction itself. Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. AD 300–800, despite significant differences in both data coverage and methodology.

  • 48.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History. Stockholm University, Faculty of Humanities, Centre for Medieval Studies.
    A regional approach to the Medieval Warm Period and the Little Ice Age2010In: Climate Change and Variability / [ed] Suzanne W. Simard & Mary E. Austin, Rijeka: Sciyo , 2010, p. 1-25Chapter in book (Other academic)
  • 49.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History. Stockholm University, Faculty of Humanities, Centre for Medieval Studies.
    Den medeltida värmeperioden i Skandinavien2009In: Sveriges historia 2: 600–1350 / [ed] Dick Harrison, Stockholm: Norstedts Förlag, 2009, p. 147-148Chapter in book (Other (popular science, discussion, etc.))
  • 50.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History. Stockholm University, Faculty of Humanities, Centre for Medieval Studies.
    Det kaotiska klimatet under senmedeltiden och Vasatiden2010In: Sveriges historia: 1350–1600 / [ed] Dick Harrison och Bo Eriksson, Stockholm: Norstedts , 2010, p. 83-86Chapter in book (Other (popular science, discussion, etc.))
12345 1 - 50 of 247
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