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- Bhend, Jonas, et al.
(författare)
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Attributing causes of regional climate change in the Baltic Sea area
- 2015
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Ingår i: Geophysical Research Abstracts.
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Konferensbidrag (refereegranskat)abstract
- Here we assess to what extent the effect of forcing mechanisms on the observed climate change in the Baltic Sea area can be detected. In particular, we assess the effect of factors causing large-scale warming (mainly anthropogenic greenhouse gases) and the regional effect of atmospheric aerosols and land-cover and land-use changes. Unfortunately, only very few targeted analyses for the Baltic catchment area are available at the moment, but findings at the regional scale are generally qualitatively consistent with global or hemispheric analyses.The observed warming in summer cannot be explained without human influence (in particular the warming effect of increasing atmospheric greenhouse gas concentrations). In other seasons and for other aspects of regional warming, findings are mixed or not significant as of yet. In addition, large-scale circulation and rainfall changes in the northern hemisphere and the Arctic have been detected to exceed natural internal variability. Other aspects of regional climate change including changes in storminess, snow properties, runoff and the changing physicalproperties of the Baltic Sea have not been formally attributed to human influence yet. Scientific understanding of the effect of aerosols on regional climate is still accumulating. It is likely that the major emission changes in Europe have had an effect on the climate in the Baltic region, the magnitude of which, however, is still unknown. Development of the modelling capability and targeted analyses are urgently needed to reduce the uncertainties related to the effect of aerosol changes on regional observed climate change. Historic deforestation and recent reforestation are the major anthropogenic land-cover changes affecting the Baltic Sea area. From all studies at hand it can be concluded that there is no evidence that anthropogenic land-cover change would be one of the forcings behind the recent warming in the Baltic region. However, past anthropogenic land-cover change may have influenced regional climate significantly already more than two thousand years ago.
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| 3. |
- Dallmeyer, Anne, et al.
(författare)
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Holocene forest-cover changes in Europe - a comparison of dynamic vegetation model results and pollen-based REVEALS reconstructions
- 2023
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Ingår i: EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11206. - : European Geosciences Union (EGU).
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Konferensbidrag (refereegranskat)abstract
- We compare Holocene forest-cover changes in Europe derived from a transient MPI-ESM1.2 simulation with high spatial resolution time-slice simulations conducted in LPJ-GUESS and pollen-based quantitative reconstructions of forest cover based on the REVEALS model (pol-RVs). The dynamic vegetation models and pol-RVs agree with respect to the general temporal trends in forest cover for most parts of Europe, with a large forest cover during the mid-Holocene and substantially smaller forest cover closer to the present time. However, the age of the start of decrease in forest cover varies between regions, and is much older in the pol-RVs than in the models. The pol-RVs suggest much earlier anthropogenic deforestation than the prescribed land-use in the models starting 2000 years ago. While LPJ-GUESS generally overestimates forest cover compared to pol-RVs, MPI-ESM indicates lower percentages of forest cover than pol-RVs, particularly in Central Europe. A comparison of the simulated climate with chironomid-based climate reconstructions reveal that model-data mismatches in forest cover are in most cases not driven by biases in the climate. Instead, sensitivity experiments show that the model results strongly depend on the models tuning regarding natural disturbance regimes (e.g. fire and wind throw). The frequency and strength of disturbances are – like most of the parameters in the vegetation models – static and calibrated to modern conditions. However, these parameter values may not be valid during climate and vegetation states totally different from today’s. In particular, the mid-Holocene natural forests were probably more stable and less sensitive to disturbances than present day forests that are heavily altered by human interventions. Our analysis highlights the fact that such model settings are inappropriate for paleo-simulations and complicate model-data comparisons with additional challenges. Moreover, our study suggests that land-use is the main driver of forest decline in Europe during the mid- and late-Holocene.
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| 6. |
- Gaillard, Marie-José, et al.
(författare)
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From land cover-climate relationships at the subcontinental scale to land cover-environment relationships at the regional and local spatial scale – the contribution of pollen-based quantitative reconstructions of vegetation cover using the Landscape Reconstruction Algorithm approach
- 2014
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Ingår i: Towards a more accurate quantification of human-environment interactions in the past. ; , s. 25-26
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Konferensbidrag (refereegranskat)abstract
- The Landscape Reconstruction Algorithm (Sugita 2007a,b) includes two models, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) that estimates vegetation abundance (% cover) within an area of ca. 100 km x 100 km, and LOVE (LOcal Vegetation Estimates) that estimates vegetation abundance at the local spatial scale, i.e. within the Relevant Source Area of Pollen (RSAP sensu Sugita, 2004) that is the smallest area around the study site for which the reconstruction is valid. The RSAP is estimated by the LOVE model and varies between sites and vegetation settings; so far, it was estimated to vary between < 1 - < 10 km in most ecological settings of the Holocene in NW Europe. We used the REVEALS model and over 600 pollen records from pollen data bases and individual researchers to reconstruct land-cover in NW Europe N of the Alps for key time windows of the Holocene in order to assess model-based reconstructions of anthropogenic land-cover change (ALCC) (e.g. Kaplan et al., 2009) and model (LPJ-GUESS) simulations of past potential (climate-induced vegetation), and to study past land cover – climate interactions using a regional climate model (RCA3). We used the REVEALS model and the complete LRA approach (REVEALS + LOVE models) along with two pollen records from large lakes and three pollen records from small bogs to reconstruct the local-scale land-cover in central Småland, southern Sweden, to study the relationship between vegetation composition, fire, climate and human impact at the regional and local spatial scales with the objective to discuss biodiversity issues. Our results suggest that i) past subcontinental to regional ALCC did influence regional climate through biogeophysical processes at the landatmosphere interface (Strandberg et al., submitted), and ii) local land-cover change, both natural and anthropogenic, govern environmental changes such as fire and biodiversity (Cui et al., 2013; Cui et al., submitted).
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| 8. |
- Gaillard, Marie-José, et al.
(författare)
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Has anthropogenic land-cover change been a significant climate forcing in the past? : An assessment for the Baltic Sea catchment area based on a literature review
- 2015
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Ingår i: Geophysical Research Abstracts.
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Konferensbidrag (refereegranskat)abstract
- We reviewed the recent published scientific literature on land cover-climate interactions at the global and regional spatial scales with the aim to assess whether it is convincingly demonstrated that anthropogenic land-cover change (ALCC) has been (over the last centuries and millennia) a significant climate forcing at the global scale, and more specifically at the scale of the Baltic Sea catchment area. The conclusions from this review are as follows: i) anthropogenic land-cover change (ALCC) is one of the few climate forcings for which the net direction of the climate response in the past is still not known. The uncertainty is due to the often counteracting temperature responses to the many biogeophysical effects, and to the biogeochemical vs biogeophysical effects; ii) there is no indication that deforestation in the Baltic Sea area since AD 1850 would have been a major cause of the recent climate warming in the region through a positive biogeochemical feedback; iii) several model studies suggest that boreal reforestation might not be an effective climate warming mitigation tool as it might lead to increased warming through biogeophysical processes; iv) palaeoecological studies indicate a major transformation of the landscape by anthropogenic activities in the southern zone of the study region occurring between 6000 and 3000/2500 calendar years before present (cal. BP) (1) ; v) the only modelling study so far of the biogeophysical effects of past ALCCs on regional climate in Europe suggests that a deforestation of the magnitude of that reconstructed for the past (between 6000 and 200 cal BP) can produce changes in winter and summer temperatures of +/- 1, the sign of the change depending on the season and the region (2). Thus, if ALCC and their biogeophysical effects did matter in the past, they should matter today and in the future. A still prevailing idea is that planting trees will mitigate climate warming through biogeochemical effects. Therefore, there is still an urgent need to better understand the biogeophysical effects on regional and continental climate of afforestation in the hemiboreal and boreal regions, and their significance in relation to the biogeochemical effects.
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| 9. |
- Gaillard, Marie-José, 1953-, et al.
(författare)
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Land cover-climate interactions in the past for the understanding of current and future climate change : the LANDCLIM project
- 2014
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Ingår i: Proceedings of the Global Land Project 2nd Open Science Meeting, Berlin,<em> </em>March 19<sup>th</sup> – 21<sup>st</sup>, 2014. - Amsterdam/Berlin/Sao Paulo : Global Land Project. ; , s. 229-230
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The LANDCLIM (LAND cover – CLIMate interactions in NW Europe during the Holocene) project has the overall aim to quantify human-induced changes in regional vegetation/land-cover in northwestern and western Europe North of the Alps during the Holocene (the last 11 500 years) with the purpose to evaluate and further refine the dynamic vegetation model LPJGUESS and the regional climate model RCA3, and to assess the possible effects on the climate development of two historical processes, i.e. climate-driven changes in vegetation and human-induced changes in land cover, via the influence of forested versus non-forested land cover on shortwave albedo, energy and water fluxes. Accounting for land surface changes may be particularly important for regional climate modeling, as the biophysical feedbacks operate at this scale. The aims of the LANDCLIM project are achieved by applying a model-data comparison scheme. The REVEALS model is used to estimate land cover from pollen data for 10 plant functional types (PFTs) and 5 time windows of the Holocene - modern time, 200 BP, 500 BP, 3000 BP and 6000 BP. The REVEALS estimates are then compared to the LPJGUESS simulations of potential vegetation and with the ALCC scenarios of Kaplan et al. (KK10) and Klein-Goldewijk et al. (HYDE). The alternative descriptions of past land-cover are then used in the regional climate model RCA3 to study the effect of anthropogenic land-cover on climate. The model-simulated climate is finally compared to palaeoclimate proxies other than pollen. The REVEALS estimates demonstrate that the study region was characterized by larger areas of human-induced openland than pollen percentages suggest, and that these areas were already very large by 3000 BP. The KK10 scenarios were found to be closer to the REVEALS estimates than the HYDE scenarios. LPJGUESS simulates potential climate-induced vegetation. The results from the RCA3 runs at 200 BP and 6000 BP using the LPJGUESS and KK10 land-cover descriptions indicate that past human-induced deforestation did produce a decrease in summer temperatures of >0 - 1.5°C due to biogeophysical processes, and that the degree of decrease differed between regions; the effect of human-induced deforestation on winter temperatures was shown to be more complex. The positive property of forests as CO2 sinks is well known. But afforestation (i.e. planting forest) may also have the opposite effect of warming the climate through biogeophysical processes. Careful studies on land cover-climate interactions are essential to understand the net result of all possible processes related to anthropogenic land-cover change so that relevant landscape management can be implemented for mitigation of climate warming.
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