| 1. |
- Callaghan, Terry V., et al.
(author)
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A new climate era in the sub-Arctic : Accelerating climate changes and multiple impacts
- 2010
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37:14, s. L14705-
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Journal article (peer-reviewed)abstract
- Climate warming in the Swedish sub-Arctic since 2000 has reached a level at which statistical analysis shows for the first time that current warming has exceeded that in the late 1930' s and early 1940' s, and has significantly crossed the 0 degrees C mean annual temperature threshold which causes many cryospheric and ecological impacts. The accelerating temperature increase trend has driven similar trends in the century-long increase in snow thickness, loss of lake ice, increases in active layer thickness, lake water TOC (total organic carbon) concentrations and the assemblages of diatoms, and changes in tree-line location and plant community structure. Some of these impacts were not evident in the first warm period of the 20th Century. Changes in climate are associated with reduced temperature variability, particularly loss of cold winters and cool summers, and an increase in extreme precipitation events that cause mountain slope instability and infrastructure failure. The long term records of multiple, local environmental factors compiled here for the first time provide detailed information for adaptation strategy development while dramatic changes in an environment particularly vulnerable to climate change highlight the need to adopt global mitigation strategies.
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| 2. |
- de Jong, R, et al.
(author)
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Climate and Peatlands
- 2010
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In: Changing Climates, Earth Systems, and Society. - 9789048187157 - 9789048187164 ; , s. 85-122
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Book chapter (other academic/artistic)
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| 3. |
- de Jong, Rixt, et al.
(author)
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Climate and Peatlands
- 2010
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In: Changing Climates, Earth Systems and Society. - Dordrecht : Springer Netherlands. - 9789048187157 - 9789048187164 ; , s. 85-121
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Book chapter (other academic/artistic)abstract
- Peatlands are an important natural archive for past climatic changes, primarily due to their sensitivity to changes in the water balance and the dating possibilities of peat sediments. In addition, peatlands are an important sink as well as potential source of greenhouse gases. The first part of this chapter discusses a range of well-established and novel proxies studied in peat cores (peat humification, macrofossils, testate amoebae, stomatal records from subfossil leaves, organic biomarkers and stable isotope ratios, aeolian sediment influx and geochemistry) that are used for climatic and environmental reconstructions, as well as recent developments in the dating of these sediments. The second part focuses on the role that peatland ecosystems may play as a source or sink of greenhouse gases. Emphasis is placed on the past and future development of peatlands in the discontinuous permafrost areas of northern Scandinavia, and the role of regenerating mined peatlands in north-western Europe as a carbon sink or source.
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| 4. |
- Gaillard, Marie-José, 1953-, et al.
(author)
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Holocene land-cover reconstructions for studies on land cover-climate feedbacks
- 2010
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In: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 6, s. 483-499
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Journal article (peer-reviewed)abstract
- The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past land-cover from pollen data, (3) to present a new project (LANDCLIM: LAND cover – CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past land-cover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The REVEALS model is demonstrated to provide better estimates of the regional vegetation/landcover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional- to continental-spatial scale throughout the Holocene. We present maps of REVEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs “grassland” and “agricultural land” at five time-windows from 6000 BP to recent time. The LANDCLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.
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| 5. |
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| 6. |
- Gallego-Sala, Angela V., et al.
(author)
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Latitudinal limits to the predicted increase of the peatland carbon sink with warming
- 2018
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In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 8:10, s. 907-
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Journal article (peer-reviewed)abstract
- The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming but it remains unclear which will dominate the global peatland response. Here we examine the global relationship between peatland carbon accumulation rates during the last millennium and planetary-scale climate space. A positive relationship is found between carbon accumulation and cumulative photosynthetically active radiation during the growing season for mid- to high-latitude peatlands in both hemispheres. However, this relationship reverses at lower latitudes, suggesting that carbon accumulation is lower under the warmest climate regimes. Projections under Representative Concentration Pathway (RCP)2.6 and RCP8.5 scenarios indicate that the present-day global sink will increase slightly until around AD 2100 but decline thereafter. Peatlands will remain a carbon sink in the future, but their response to warming switches from a negative to a positive climate feedback (decreased carbon sink with warming) at the end of the twenty-first century.
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| 7. |
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| 8. |
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| 9. |
- Klaminder, Jonatan, et al.
(author)
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Lead Contamination of Subarctic Lakes and Its Response to Reduced Atmospheric Fallout : Can the Recovery Process Be Counteracted by the Ongoing Climate Change?
- 2010
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In: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 44:7, s. 2335-2340
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Journal article (peer-reviewed)abstract
- Can a climate-triggered export of old contaminants from the soil alter the lead (Pb) contaminant burden of subarctic lakes? To address this question, we reconstructed the pollution history of three high latitude lakes situated in a region where a recent climatic shift has occurred. Dated sediment records were used as archives of past Pb inputs to the lakes, where the difference in the Pb-206/Pb-207 ratio between atmospheric contaminants (Pb-206/Pb-207 ratio <1.16) and geogenic Pb in the catchment soil (Pb-206/Pb-207 ratio >1.22) were used to trace fluxes of Pb contaminants. Lead contaminants were found in sediments deposited since Roman times. A significant export of Pb from the soil contaminant pool is indicated in two of the lakes surrounded by near-shore permafrost soils. Here, levels of Pb contaminants and Pb-206/Pb-207 ratios of sediments deposited after the 1970s appear not to have been strongly affected by the >= 90% reduction in atmospheric deposition rates and increasing Pb-206/Pb-207 ratios of atmospheric Pb since the 1990s. We concluded that soil processes stimulated by the ongoing climate change at high latitudes might work counteractive to efforts to reduce contaminant levels in subarctic lakes.
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| 10. |
- Kokfelt, Ulla, et al.
(author)
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Diatoms in peat : dominant producers in a changing environment?
- 2009
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In: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 41:8, s. 1764-1766
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Journal article (peer-reviewed)abstract
- Changes in hydrology and temperature can induce rapid changes in boreal wetland ecosystems. Factors such as hydrosere, permafrost, climate and human interference may disturb the prevailing mire vegetation, whereby a new dominant assemblage can develop. At the transition from one vegetation type to another, the old vegetation may be suppressed, die out or start to decay, and some time may pass until a new mire vegetation is fully established. Here, we demonstrate that diatoms may thrive during such transitions, creating isolated and shallow peat layers with significantly elevated biogenic silica content. Biogenic silica and other nutrients that would otherwise be lost during mineralization in runoff are in this way retained in the ecosystem. Our results imply that silica storage originating from diatoms can be expected to increase in today’s rapidly changing boreal wetlands. The impacts on transport of Si through boreal watersheds are currently unknown.
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| 11. |
- Kokfelt, Ulla, et al.
(author)
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Ecosystem responses to increased precipitation and permafrost decay in subarctic Sweden inferred from peat and lake sediments
- 2009
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 15:7, s. 1652-1663
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Journal article (peer-reviewed)abstract
- Recent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrophic areas leading to significant changes in carbon cycling in the mire. In order to track these changes through time and evaluate potential forcing mechanisms, this paper analyses a peat succession and a lake sediment sequence from within the mire, providing a record for the last 100 years, and compares these with monitored climate and active layer thickness data. The peat core was analysed for testate amoebae to reconstruct changes in peatland surface moisture conditions and water table fluctuations. The lake sediment core was analysed by near infrared spectroscopy to infer changes in the total organic carbon (TOC) concentration of the lake-water, and changes in δ13C and C, N and δ15N to track changes in the dissolved inorganic carbon (DIC) pool and the influence of diagenetic effects on sediment organic matter, respectively. Results showed that major shifts towards increased peat surface moisture and TOC concentration of the lake-water occurred around 1980, one to two decades earlier than a temperature driven increase in active layer thickness. Comparison with monitored temperature and precipitation from a nearby climate station indicates that this change in peat surface moisture is related to June–September (JJAS) precipitation and that the increase in lake-water TOC concentration reflects an increase in total annual precipitation. A significant depletion in 13C of sediment organic matter in the early 1980s probably reflects the effect of a single or a few consecutive years with anomalously high summer precipitation, resulting in elevated DIC content of the lake water, predominantly originating from increased export and subsequent respiration of organic carbon from the mire. Based on these results, it was not possible to link proxy data obtained on peat and lake-sediment records directly to permafrost decay. Instead our data indicate that increased precipitation and anomalously high rainfall during summers had a significant impact on the mire and the adjacent lake ecosystem. We therefore propose that effects of increased precipitation should be considered when evaluating potential forcing mechanisms of recent changes in carbon cycling in the subarctic.
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| 12. |
- Kokfelt, Ulla, et al.
(author)
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Solar forcing of climate during the last millennium recorded in lake sediments from northern Sweden
- 2013
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In: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 23:3, s. 447-452
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Journal article (peer-reviewed)abstract
- We report on a sediment record from a small lake within the subarctic wetland complex Stordalen in northernmost Sweden covering the last 1000 years. Variations in the content of minerogenic material are found to follow reconstructed variations in the activity of the Sun between the 13th and 18th centuries. Periods of low solar activity are associated with minima in minerogenic material and vice versa. A comparison between the sunspot cycle and a long instrumental series of summer precipitation further reveals a link between the 11 yr solar cycle and summer precipitation variability since around 1960. Solar minima are in this period associated with minima in summer precipitation, whereas the amount of summer precipitation increases during periods with higher solar activity. Our results suggest that the climate responds to both the 11 yr solar cycle and to long-term changes in solar activity and in particular solar minima, causing dry conditions with resulting decreased runoff.
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| 13. |
- Kokfelt, Ulla
(author)
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Subarctic ecosystem responses to climate, catchment and permafrost dynamics in the Holocene
- 2009
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Doctoral thesis (other academic/artistic)abstract
- This thesis assesses aspects of the wetland development, permafrost dynamics and associated changes in carbon and nutrient cycling of the Stordalen Mire in northern Sweden. Various ecological and biogeochemical analyses of one peat and two lake sediment sequences were conducted, including analyses of organic matter and carbonate content, mosses, diatoms, testate amoebae, pigments, carbon and nitrogen and their stable isotopes, near infrared spectroscopy and biogenic silica. Results revealed that the structural development of the mire occurred during the later part of the Holocene. Peat inception was dated at 4700 cal BP and onset of organic sedimentation in two adjacent lake basins occurred at 3400 and 2650 cal BP. Fen peat accumulated until minimum 2800 cal BP, and after c.2650 cal BP an early permafrost aggradation phase likely caused frost heave and significant changes in the wetland structure and hydrology. Peat is largely missing in the examined core between 2800 and 1350 cal BP, reflecting either environmental stress causing a decrease/cease of peat accumulation and/or erosion of previously formed peat. An increased content of redeposited peat in one of the lakes after c.2100 cal BP, points to mire erosion caused by permafrost decay. A high nutrient/productivity layer in the other lake between 1900 and 1800 cal BP may have been related to the same event in the mire. Sedge peat accumulated from 1350 cal BP. Renewed permafrost aggradation is indicated indirectly around 700 cal BP and directly 120 cal BP from changes in peat building vegetation. Fen peat and transitions between dominating mire vegetation communities were characterized by frequent diatoms and high nutrient concentrations. Permafrost phases were associated with poor fen and bog formation, and thus considerably more acidic conditions in the mire as compared to pH conditions when richer fen communities dominated. This development resulted in more acidic runoff to adjacent lakes and affected carbonate precipitation there. Further, poor catchment retention of nutrients during poor fen/bog stages, probably caused increased fluxes of nutrients out of the system, stimulating primary lake productivity in adjacent lakes. Increased lake productivity in turn caused increased oxygen consumption for decomposition at the lake bottom, and thus anoxic conditions. Thereby an increased flux of phosphorous from the sediment triggered a state of self-sustained eutrophication during two centuries, preceding the onset of 20th century permafrost thaw. Proxy indications of peat surface moisture conditions and lake-water TOC concentration dynamics during the last 100 years were reconstructed by means of testate amoebae assemblages in peat and near infrared spectroscopy and the carbon isotopic composition of lake sediment bulk organic matter. These results revealed a close connection with decadal trends of total annual and summer precipitation as well as single years with anomalously high precipitation, especially in the late summer. The data could thus not be directly linked to monitored trends in active layer thickness.
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| 14. |
- Kokfelt, Ulla, et al.
(author)
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Wetland development, permafrost history and nutrient cycling inferred from late Holocene peat and lake sediment records in subarctic Sweden
- 2010
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 44:1, s. 327-342
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Journal article (peer-reviewed)abstract
- Permafrost in peatlands of subarctic Sweden is presently thawing at accelerated rates, which raises questions about the destiny of stored carbon and nutrients and impacts on adjacent freshwater ecosystems. In this study we use peat and lake sediment records from the Stordalen palsa mire in northern Sweden to address the late Holocene (5,000 cal BP-present) development of the mire as well as related changes in carbon and nutrient cycling. Formation, sediment accumulation and biogeochemistry of two studied lakes are suggested to be largely controlled by the development of the mire and its permafrost dynamics. Peat inception took place at ca. 4,700 cal BP as a result of terrestrialisation. Onset of organic sedimentation in the adjacent lakes occurred at ca. 3,400 and 2,650 cal BP in response to mire expansion and permafrost aggradation, respectively. Mire erosion, possibly due to permafrost decay, led to re-deposition of peat into one of the lakes after ca. 2,100 cal BP, and stimulated primary productivity in the other lake at ca. 1,900-1,800 cal BP. Carbonate precipitation appears to have been suppressed when acidic poor fen and bog (palsa) communities dominated the catchment mire, and permafrost-induced changes in hydrology may further have affected the inflow of alkaline water from the catchment. Elevated contents of biogenic silica and diatom pigments in lake sediments during periods of poor fen and bog expansion further indicate that terrestrial vegetation influenced the amount of nutrients entering the lake. Increased productivity in the lake likely caused bottom-water anoxia in the downstream lake and led to recycling of sediment phosphorous, bringing the lake into a state of self-sustained eutrophication during two centuries preceding the onset of twentieth century permafrost thaw. Our results give insight into nutrient and permafrost dynamics in a subarctic wetland and imply that continued permafrost decay and related vegetation changes towards minerotrophy may increase carbon and nutrient storage of mire deposits and reduce nutrient fluxes in runoff. Rapid permafrost degradation may on the other hand lead to widespread mire erosion and to relatively short periods of significantly increased nutrient loading in adjacent lakes.
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| 15. |
- Loisel, Julie, et al.
(author)
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A database and synthesis of northern peatland soil properties and Holocene carbon and nitrogen accumulation
- 2014
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In: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 24:9, s. 1028-1042
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Journal article (peer-reviewed)abstract
- Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45 degrees N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 +/- 3% (standard deviation) for Sphagnum peat, 51 +/- 2% for non-Sphagnum peat, and at 49 +/- 2% overall. Dry bulk density averaged 0.12 +/- 0.07 g/cm(3), organic matter bulk density averaged 0.11 +/- 0.05 g/cm(3), and total carbon content in peat averaged 47 +/- 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 +/- 2 (standard error of mean) g C/m(2)/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25-28 g C/m(2)/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.
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| 16. |
- Rundgren, Mats, et al.
(author)
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Holocene wet shifts in NW European bogs : evidence for the roles of external forcing and internal feedback from a high-resolution study of peat properties, plant macrofossils and testate amoebae
- 2023
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In: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 38:3, s. 423-439
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Journal article (peer-reviewed)abstract
- Two conspicuous wet shifts in the peat stratigraphy of Store Mosse in southern Sweden, associated with bog-wide changes in vegetation and degree of peat decomposition, were analysed at high resolution. The bog-surface wetness (BSW) proxy data (organic matter bulk density, C/N ratio, plant macrofossils and testate amoebae) highlight the importance of interactions between vegetation composition, microtopography and degree of peat decomposition, and show that the bog system operated consistently during the two wet shifts (dated to c. 2700 and 1000 cal a bp) despite different internal and external conditions. A sensitive bog-system state, associated with a degraded microtopography and well-decomposed surface peat with low hydrological conductivity developed during sustained dry conditions, probably contributed to the large BSW amplitudes registered. Comparable bog systems are expected to operate in the same way, and regionally high sensitivity that developed in response to atmospheric circulation changes may partly explain synchronous registration of wet shifts. The wet shifts in Store Mosse were attributed to solar and volcanic forcing, respectively, and wet shifts of similar magnitude registered in other NW European bogs are likely to also have been externally forced.
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| 17. |
- Strandberg, Gustav, et al.
(author)
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Regional climate model simulations for Europe at 6 and 0.2 k BP : sensitivity to changes in anthropogenic deforestation
- 2014
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In: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 10:2, s. 661-680
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Journal article (peer-reviewed)abstract
- This study aims to evaluate the direct effects of anthropogenic deforestation on simulated climate at two contrasting periods in the Holocene, similar to 6 and similar to 0.2 k BP in Europe. We apply We apply the Rossby Centre regional climate model RCA3, a regional climate model with 50 km spatial resolution, for both time periods, considering three alternative descriptions of the past vegetation: (i) potential natural vegetation (V) simulated by the dynamic vegetation model LPJ-GUESS, (ii) potential vegetation with anthropogenic land use (deforestation) from the HYDE3.1 (History Database of the Global Environment) scenario (V + H3.1), and (iii) potential vegetation with anthropogenic land use from the KK10 scenario (V + KK10). The climate model results show that the simulated effects of deforestation depend on both local/regional climate and vegetation characteristics. At similar to 6 k BP the extent of simulated deforestation in Europe is generally small, but there are areas where deforestation is large enough to produce significant differences in summer temperatures of 0.5-1 degrees C. At similar to 0.2 k BP, extensive deforestation, particularly according to the KK10 model, leads to significant temperature differences in large parts of Europe in both winter and summer. In winter, deforestation leads to lower temperatures because of the differences in albedo between forested and unforested areas, particularly in the snow-covered regions. In summer, deforestation leads to higher temperatures in central and eastern Europe because evapotranspiration from unforested areas is lower than from forests. Summer evaporation is already limited in the southernmost parts of Europe under potential vegetation conditions and, therefore, cannot become much lower. Accordingly, the albedo effect dominates in southern Europe also in summer, which implies that deforestation causes a decrease in temperatures. Differences in summer temperature due to deforestation range from -1 degrees C in south-western Europe to +1 degrees C in eastern Europe. The choice of anthropogenic land-cover scenario has a significant influence on the simulated climate, but uncertainties in palaeoclimate proxy data for the two time periods do not allow for a definitive discrimination among climate model results.
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| 18. |
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