| 1. |
- Chen, Deliang, 1961, et al.
(author)
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Summary of a workshop on extreme weather events in a warming world organized by the Royal Swedish Academy of Sciences
- 2020
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In: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 1600-0889 .- 0280-6509. ; 72:1
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Journal article (peer-reviewed)abstract
- Climate change is not only about changes in means of climatic variables such as temperature, precipitation and wind, but also their extreme values which are of critical importance to human society and ecosystems. To inspire the Swedish climate research community and to promote assessments of international research on past and future changes in extreme weather events against the global climate change background, the Earth Science Class of the Royal Swedish Academy of Sciences organized a workshop entitled 'Extreme weather events in a warming world' in 2019. This article summarizes and synthesizes the key points from the presentations and discussions of the workshop on changes in floods, droughts, heat waves, as well as on tropical cyclones and extratropical storms. In addition to reviewing past achievements in these research fields and identifying research gaps with a focus on Sweden, future challenges and opportunities for the Swedish climate research community are highlighted.
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| 2. |
- Rundgren, Mats, et al.
(author)
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Dynamic sea-level change during the last deglaciation of northern Iceland
- 1997
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In: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 26:3, s. 201-215
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Journal article (peer-reviewed)abstract
- A detailed reconstruction of deglacial relative sea-level changes at the northern coast of Iceland, based on the litho- and biostratigraphy of lake basins, indicates an overall fall in relative sea level of about 45 m between 11 300 and 9100 BP, corresponding to an isostatic rebound of 77 m. The overall regression was interrupted by two minor transgressions during the late Younger Dryas and in early Preboreal, and these were probably caused by a combination of expansions of local ice caps and readvances of the Icelandic inland ice-sheet margin. Maximum absolute uplift rates are recorded during the regressional phase between the two transgressions (10 000-9850 BP), with a mean value of c. 15 cm ·14C yr-1 or 11-12 cm ·cal. yr-1. Mean absolute uplift during the regressional phase following the second transgression (9700-9100 BP) was around 6 cm ·14C yr-1, corresponding to c. 3 cm · cal. yr-1, and relative sea level dropped below present-day sea level at 9000 BP.
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| 3. |
- Björck, Svante, et al.
(author)
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A South Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial
- 2019
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In: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 15:6, s. 1939-1958
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Journal article (peer-reviewed)abstract
- Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..
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| 4. |
- John Lowe, J., et al.
(author)
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Inter-regional correlation of palaeoclimatic records for the last Glacial-Interglacial Transition : A protocol for improved precision recommended by the INTIMATE project group
- 2001
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In: Quaternary Science Reviews. - 0277-3791. ; 20:11, s. 1175-1187
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Journal article (peer-reviewed)abstract
- The remit of the INTIMATE project of the INQUA Palaeoclimate Commission is to synthesise marine, terrestrial and ice-core data for the North Atlantic region during the Last Glacial-Interglacial Transition (LGIT: ca 13-1014C kyr BP; ca 15-11.5 ice-core kyr BP). A major problem, however, is the difficulty of effecting correlations at a temporal resolution that are adequate for defining 'leads' and 'lags' between the polar ice, terrestrial, marine, and atmospheric realms. The limitations of the dating and correlation methods currently employed are summarised, and new quality assurance protocols are proposed. These include recommendations on the contextual information that should accompany radiocarbon dates, procedures for radiocarbon calibration, the use of an event-stratigraphic approach in inter-regional correlations, and the more widespread use of time-parallel marker horizons (based on tephra layers, oxygen isotope stratigraphy, palaeomagnetic stratigraphy, and radiocarbon 'wiggle-matching') to underpin the geochronology and correlation of events during the LGIT. These protocols will be adopted by the INTIMATE project in future international, collaborative research and are recommended to other groups working on this important time period.
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| 5. |
- Mckay, Claire, et al.
(author)
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The interplay between the surface and bottom water environment within the Benguela Upwelling System over the last 70 ka
- 2016
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In: Paleoceanography. - 0883-8305. ; 31:2, s. 266-285
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Journal article (peer-reviewed)abstract
- The Benguela Upwelling System (BUS), located between 30 and 20°S, is one of the fundamental high-productivity systems of the world ocean. The BUS has previously been studied in terms of primary productivity and ecology over glacial-interglacial timescales; however, the response and coupling with the benthic environment have received little attention. Here, for the first time, we present a high-resolution reconstruction of the BUS highlighting the link between surface and benthic productivity and their response to climatic and oceanographic changes over the last 70 ka. The study is based on benthic foraminiferal faunal analysis together with analyses of diatom assemblages, grain size of the terrigenous fraction, and stable O and C isotopic and bulk biogenic components of core GeoB3606-1. We reveal significant shifts in benthic foraminiferal assemblage composition. Tight coupling existed between the surface and bottom water environment especially throughout marine isotope stages 4 and 3 (MIS4 and MIS3). Due to the high export production, the site has essentially experienced continuous low oxygen conditions; however, there are time periods where the hypoxic conditions were even more notable. Two of these severe hypoxic periods were during parts of MIS4 and MIS3 where we find an inverse relationship between diatom and benthic foraminifera accumulation, meaning that during times of extremely high phytodetritus export we note strongly suppressed benthic productivity. We also stress the importance of food source for the benthos throughout the record. Shifts in export productivity are attributed not only to upwelling intensity and filament front position, but also, regional-global climatic and oceanographic changes had significant impact on the BUS dynamics.
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| 6. |
- Schenk, Frederik, et al.
(author)
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Floral evidence for high summer temperatures in southern Scandinavia during 15-11 cal ka BP
- 2020
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 233
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Journal article (peer-reviewed)abstract
- The global climate transition from the Lateglacial to the Early Holocene is dominated by a rapid warming trend driven by an increase in orbital summer insolation over high northern latitudes and related feedbacks. The warming trend was interrupted by several abrupt shifts between colder (stadial) and warmer (interstadial) climate states following instabilities of the Atlantic Meridional Overturning Circulation (AMOC) in response to rapidly melting ice sheets. The sequence of abrupt shifts between extreme climate states had profound impacts on ecosystems which make it challenging to reliably quantify state variables like July temperatures within a non-analogue climate envelope. For Europe, there is increasing albeit inconclusive evidence for higher stadial summer temperatures than initially thought. Here we present a comprehensive floral compilation of plant macrofossils from lake sediment cores of 15 sites from S-Scandinavia covering the period similar to 15 to 11 ka BP. We find evidence for a continued presence of plant species indicating high July temperatures throughout the last deglaciation. The presence of hemiboreal plants in close vicinity to the southern margin of the Fennoscandian Ice Sheet implies a strong thermal summer forcing for the rapid ice sheet melt. Consistent with some recent studies, we do not find evidence for a general stadial summer cooling, which indicates that other reasons than summer temperatures caused drastic setbacks in proxy signals possibly driven by extreme winter cooling and/or shorter warm seasons.
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| 7. |
- Schenk, Frederik, et al.
(author)
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Warm summers during the Younger Dryas cold reversal
- 2018
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Journal article (peer-reviewed)abstract
- The Younger Dryas (YD) cold reversal interrupts the warming climate of the deglaciation with global climatic impacts. The sudden cooling is typically linked to an abrupt slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in response to meltwater discharges from ice sheets. However, inconsistencies regarding the YD-response of European summer temperatures have cast doubt whether the concept provides a sufficient explanation. Here we present results from a high-resolution global climate simulation together with a new July temperature compilation based on plant indicator species and show that European summers remain warm during the YD. Our climate simulation provides robust physical evidence that atmospheric blocking of cold westerly winds over Fennoscandia is a key mechanism counteracting the cooling impact of an AMOC-slowdown during summer. Despite the persistence of short warm summers, the YD is dominated by a shift to a continental climate with extreme winter to spring cooling and short growing seasons.
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| 8. |
- Johnson, Mark D., 1954, et al.
(author)
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Varved glaciomarine clay in central Sweden before and the Baltic Ice Lake drainage: a further clue to the drainage event at Mt. Bilingen
- 2013
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In: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 135:3-4, s. 293-307
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Journal article (peer-reviewed)abstract
- Glaciomarine clay found west of Mt Billingen, central Sweden, contains two distinct varve units separated by a sand layer that we interpret to be sediment deposited in the North Sea during the catastrophic drainage of the Baltic Ice Lake (BIL). The lower varve series was deposited proximal to the retreating ice margin and consists of varves that grade upward from gray to red. The upper varve series was deposited after the drainage event when fresh water within the Baltic basin flowed westward north of Billingen; the upper varves grade from red to gray. Grain size, elemental composition (determined by X-ray fluorescence (XRF)), iron and organic-carbon content vary within each varve, with values that grade upward through each varve, but with a sharp contact with the overlying varve. The two varve units differ from each other, with the lower sequence being coarser and the upper containing a higher iron and organic-carbon content. We attribute the differences between pre- and post-drainage varves to reflect changes in distance to the ice margin and provenance. The stratigraphy at the site suggests that the BIL drainage lasted ,1 year. Lithostratigraphic correlations to the Lake La°ngen basin west of Mt Billingen support the idea of glacier ice in the La°ngen basin during the drainage and a retreat and advance of the ice sheet during Allero¨d and Younger Dryas, including the possibility of an earlier, Allero¨d drainage.
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| 9. |
- Björck, Svante, et al.
(author)
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Historiska varningssignaler
- 2010
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In: Sverige i nytt klimat - våtvarm utmaning. - Stockholm : Forskningsrådet Formas. - 9789154060405 ; , s. 71-86
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Book chapter (pop. science, debate, etc.)abstract
- 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.
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| 10. |
- Björck, Svante
(author)
-
Policy brief: Paleoklimatet informerar oss om framtiden
- 2013
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In: Klimat i Fokus/MERGE. ; 4
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Other publication (pop. science, debate, etc.)abstract
- Paleoklimatologi – läran om hur klimatet utvecklats genom jordens historia – ger oss referensramar för att sätta dagens klimat och möjliga framtida klimatförändringar i ett historiskt perspektiv. Till exempel visar nya analyser av historiska klimatarkiv att för norra halvklotet var perioden 1983-2012 sannolikt den varmaste på 1400 år. Vi ser även att vid den senaste värmeperioden, för 125 000 år sedan, var den globala medeltemperaturen troligen endast 1-2 grader högre jämfört med industrialismens början 1850, och att detta sammanföll med minst 6 m högre havsnivåer än dagens.
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