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Showing papers by "Potsdam Institute for Climate Impact Research published in 2004"


Journal ArticleDOI
TL;DR: In this paper, the authors used ground observations, remote sensing, and analysis of the atmospheric CO2 signal to estimate the progression of vegetation activity in the spring season, and found that the correlation between estimates of the initiation of spring activity derived from ground observations and remote sensing at interannual time scales is often weak.
Abstract: Summary Climate change effects on seasonal activity in terrestrial ecosystems are significant and well documented, especially in the middle and higher latitudes. Temperature is a main driver of many plant developmental processes, and in many cases higher temperatures have been shown to speed up plant development and lead to earlier switching to the next ontogenetic stage. Qualitatively consistent advancement of vegetation activity in spring has been documented using three independent methods, based on ground observations, remote sensing, and analysis of the atmospheric CO2 signal. However, estimates of the trends for advancement obtained using the same method differ substantially. We propose that a high fraction of this uncertainty is related to the time frame analysed and changes in trends at decadal time scales. Furthermore, the correlation between estimates of the initiation of spring activity derived from ground observations and remote sensing at interannual time scales is often weak. We propose that this is caused by qualitative differences in the traits observed using the two methods, as well as the mixture of different ecosystems and species within the satellite scenes.

869 citations


Journal ArticleDOI
TL;DR: In this paper, the hydrological performance of the Lund-Potsdam-Jena model (LPJ), a prominent dynamic global vegetation model, is evaluated, and it is shown that runoff and evapotranspiration computed by LPJ agree well with respective results from state-of-the-art global hydrologogical models, while in some regions, runoff is significantly over- or underestimated compared to observations.

843 citations


Journal ArticleDOI
TL;DR: General guidance is offered as to the methodology of change detection in time series of hydrological data, embracing stages such as preparing a suitable data set, exploratory analysis, application of adequate statistical tests and interpretation of results.
Abstract: General guidance is offered as to the methodology of change detection in time series of hydrological data, embracing stages such as preparing a suitable data set, exploratory analysis, application of adequate statistical tests and interpretation of results. Although the paper cannot go into full details of the many existing tests, it gives an easy-to-follow overview, offering practical hints and describing caveats and misconceptions. It serves as a refresher, raising attention to essential things that have often been ignored. A particular recommendation of the paper is that greater use of distribution-free testing methods, particularly resampling methods, should be made. These methods are recommended because they are particularly suited to hydrological data, which are often strongly skewed (non-normal), seasonal and serially correlated. Resampling techniques are flexible, robust and powerful, and require only minimal assumptions to be made about the data.

482 citations


Journal ArticleDOI
TL;DR: The physical interactions between polynyas and the atmosphere-sea ice-ocean system are investigated in this article, where the surface heat budget and water mass transformation within these features are addressed.
Abstract: [1] Polynyas are nonlinear-shaped openings within the ice cover, ranging in size from 10 to 105 km2. Polynyas play an important climatic role. First, winter polynyas tend to warm the atmosphere, thus affecting atmospheric mesoscale motions. Second, ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection, contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation. Since 1990, there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas. This article reviews polynya research carried out in the last 2 decades, focusing on presenting a state-of-the-art picture of the physical interactions between polynyas and the atmosphere-sea ice-ocean system. Observational and modeling studies, the surface heat budget, and water mass transformation within these features are addressed.

301 citations


Journal ArticleDOI
TL;DR: A robust alternative to prediction that is based on using integrated assessments within the framework of vulnerability studies is suggested and a number of research priorities and the establishment of education programs in Earth Systems Science are recommended.
Abstract: The Earth's climate system is highly nonlinear: inputs and outputs are not proportional, change is often episodic and abrupt, rather than slow and gradual, and multiple equilibria are the norm. While this is widely accepted, there is a relatively poor understanding of the different types of nonlinearities, how they manifest under various conditions, and whether they reflect a climate system driven by astronomical forcings, by internal feedbacks, or by a combination of both. In this paper, af- ter a brief tutorial on the basics of climate nonlinearity, we provide a number of illustrative examples and highlight key mechanisms that give rise to nonlinear behavior, address scale and methodological issues, suggest a robust alternative to prediction that is based on using integrated assessments within the framework of vulnerability studies and, lastly, recommend a number of research priorities and the establishment of education programs in Earth Systems Science. It is imperative that the Earth's climate system research community embraces this nonlinear paradigm if we are to move forward in the assessment of the human influence on climate.

284 citations


Journal ArticleDOI
TL;DR: In this article, the role of changing natural (volcanic, aerosol, insolation) and anthropogenic (CO2 emissions, land cover) forcings on the global climate system over the last 150 years using an earth system model of intermediate complexity, CLIMBER-2.
Abstract: We assess the role of changing natural (volcanic, aerosol, insolation) and anthropogenic (CO2 emissions, land cover) forcings on the global climate system over the last 150 years using an earth system model of intermediate complexity, CLIMBER-2. We apply several datasets of historical land-use reconstructions: the cropland dataset by Ramankutty & Foley (1999) (R&F), the HYDE land cover dataset of Klein Goldewijk (2001), and the land-use emissions data from Houghton & Hackler (2002). Comparison between the simulated and observed temporal evolution of atmospheric CO2 and d 13 CO2 are used to evaluate these datasets. To check model uncertainty, CLIMBER-2 was coupled to the more complex Lund–Potsdam–Jena (LPJ) dynamic global vegetation model. In simulation with R&F dataset, biogeophysical mechanisms due to land cover changes tend to decrease global air temperature by 0.261C, while biogeochemical mechanisms act to warm the climate by 0.181C. The net effect on climate is negligible on a global scale, but pronounced over the land in the temperate and high northern latitudes where a cooling due to an increase in land surface albedo offsets the warming due to land-use CO2 emissions. Land cover changes led to estimated increases in atmospheric CO2 of between 22 and 43ppmv. Over the entire period 1800–2000, simulated d 13 CO2 with HYDE compares most favourably with ice core during 1850–1950 and Cape Grim data, indicating preference of earlier land clearance in HYDE over R&F. In relative terms, land cover forcing corresponds to 25–49% of the observed growth in atmospheric CO2. This contribution declined from 36–60% during 1850–1960 to 4–35% during 1960–2000. CLIMBER-2-LPJ simulates the land cover contribution to atmospheric CO2 growth to decrease from 68% during 1900–1960 to 12% in the 1980s. Overall, our simulations show a decline in the relative role of land cover changes for atmospheric CO2 increase during the last 150 years.

253 citations


Journal ArticleDOI
TL;DR: Estimates of additional carbon emissions during the twenty-first century, for all climate and deforestation scenarios, range from 101 to 367 Gt C, resulting in CO2 concentration increases above background values between 29 and 129 p.p.m.
Abstract: The remaining carbon stocks in wet tropical forests are currently at risk because of anthropogenic deforestation, but also because of the possibility of release driven by climate change. To identify the relative roles of CO2 increase, changing temperature and rainfall, and deforestation in the future, and the magnitude of their impact on atmospheric CO2 concentrations, we have applied a dynamic global vegetation model, using multiple scenarios of tropical deforestation (extrapolated from two estimates of current rates) and multiple scenarios of changing climate (derived from four independent offline general circulation model simulations). Results show that deforestation will probably produce large losses of carbon, despite the uncertainty about the deforestation rates. Some climate models produce additional large fluxes due to increased drought stress caused by rising temperature and decreasing rainfall. One climate model, however, produces an additional carbon sink. Taken together, our estimates of additional carbon emissions during the twenty-first century, for all climate and deforestation scenarios, range from 101 to 367 Gt C, resulting in CO2 concentration increases above background values between 29 and 129 p.p.m. An evaluation of the method indicates that better estimates of tropical carbon sources and sinks require improved assessments of current and future deforestation, and more consistent precipitation scenarios from climate models. Notwithstanding the uncertainties, continued tropical deforestation will most certainly play a very large role in the build-up of future greenhouse gas concentrations.

246 citations


Journal ArticleDOI
TL;DR: In this article, the authors reconstructed annual precipitation for the last 2,500 years in northeastern Qinghai from living and archaeological juniper trees, and found that a dominant feature of the precipitation of this area is a high degree of variability in mean rainfall at annual, decadal, and centennial scales, with many wet and dry periods that are corroborated by other paleoclimatic indicators.
Abstract: Annual precipitation for the last 2,500 years was reconstructed for northeastern Qinghai from living and archaeological juniper trees. A dominant feature of the precipitation of this area is a high degree of variability in mean rainfall at annual, decadal, and centennial scales, with many wet and dry periods that are corroborated by other paleoclimatic indicators. Reconstructed values of annual precipitation vary mostly from 100 to 300 mm and thus are no different from the modern instrumental record in Dulan. However, relatively dry years with below-average precipitation occurred more frequently in the past than in the present. Periods of relatively dry years occurred during 74–25 BC, AD 51–375, 426–500, 526–575, 626–700, 1100–1225, 1251–1325, 1451–1525, 1651–1750 and 1801–1825. Periods with a relatively wet climate occurred during AD 376–425, 576–625, 951–1050, 1351–1375, 1551–1600 and the present. This variability is probably related to latitudinal positions of winter frontal storms. Another key feature of precipitation in this area is an apparently direct relationship between interannual variability in rainfall with temperature, whereby increased warming in the future might lead to increased flooding and droughts. Such increased climatic variability might then impact human societies of the area, much as the climate has done for the past 2,500 years.

234 citations


Journal ArticleDOI
TL;DR: In this paper, a method is introduced to estimate the proximity of climate sub-systems to non-linear thresholds by measuring the smallest decay rate of the system under investigation and to consider its trend.
Abstract: [1] A method is introduced to estimate the proximity of climate sub-systems to non-linear thresholds. We suggest to measure the smallest decay rate of the system under investigation and to consider its trend. We argue that this is the diagnostic variable most directly linked to the distance from a bifurcation threshold. With the climate model of intermediate complexity CLIMBER2 we demonstrate our method for the North Atlantic thermohaline circulation. It is shown that proper analysis of paleo information could significantly reduce the uncertainty which plagues current estimates of the distance from the shutdown of the thermohaline circulation.

230 citations


Journal ArticleDOI
TL;DR: In this paper, the authors study the inference of long-range correlations by means of Detrended Fluctuation Analysis (DFA) and argue that power-law scaling of the fluctuation function and thus long-memory may not be assumed a priori but have to be established.
Abstract: We study the inference of long-range correlations by means of Detrended Fluctuation Analysis (DFA) and argue that power-law scaling of the fluctuation function and thus long-memory may not be assumed a priori but have to be established. This requires the investigation of the local slopes. We account for the variability characteristic for stochastic processes by calculating empirical confidence regions. Comparing a long-memory with a short-memory model shows that the inference of long-range correlations from a finite amount of data by means of DFA is not specific. We remark that scaling cannot be concluded from a straight line fit to the fluctuation function in a log-log representation. Furthermore, we show that a local slope larger than α=0.5 for large scales does not necessarily imply long-memory. We also demonstrate, that it is not valid to conclude from a finite scaling region of the fluctuation function to an equivalent scaling region of the autocorrelation function. Finally, we review DFA results for the Prague temperature data set and show that long-range correlations cannot not be concluded unambiguously.

191 citations


Journal ArticleDOI
TL;DR: Climate envelope models provide the best approach currently available for evaluating reliably the potential impacts of future climate change upon biodiversity, and goodness-of-fit measures showed that useful models were fitted for >96% of species.
Abstract: Species–climate ‘envelope’ models are widely used to evaluate potential climate change impacts upon species and biodiversity. Previous studies have used a variety of methods to fit models making it difficult to assess relative model performance for different taxonomic groups, life forms or trophic levels. Here we use the same climatic data and modelling approach for 306 European species representing three major taxa (higher plants, insects and birds), and including species of different life form and from four trophic levels. Goodness-of-fit measures showed that useful models were fitted for >96% of species, and that model performance was related neither to major taxonomic group nor to trophic level. These results confirm that such climate envelope models provide the best approach currently available for evaluating reliably the potential impacts of future climate change upon biodiversity.

01 Jan 2004
TL;DR: In this article, the authors examine different concepts of a "warming commitment" which are often used in various ways to describe or imply that a certain level of warming is irrevocably committed to over time frames such as the next 50 to 100 years, or longer.
Abstract: This paper examines different concepts of a ‘warming commitment’ which is often used in various ways to describe or imply that a certain level of warming is irrevocably committed to over time frames such as the next 50 to 100 years, or longer. We review and quantify four different concepts, namely (1) a ‘constant emission warming commitment’, (2) a ‘present forcing warming commitment’, (3) a‘zero emission (geophysical) warming commitment’ and (4) a ‘feasible scenario warming commitment’. While a ‘feasible scenario warming commitment’ is probably the most relevant one for policy making, it depends centrally on key assumptions as to the technical, economic and political feasibility of future greenhouse gas emission reductions. This issue is of direct policy relevance when one considers that the 2002 global mean temperatures were 0.8± 0.2 ∘C above the pre-industrial (1861–1890) mean and the European Union has a stated goal of limiting warming to 2 ∘C above the pre-industrial mean: What is the risk that we are committed to overshoot 2 ∘C? Using a simple climate model (MAGICC) for probabilistic computations based on the conventional IPCC uncertainty range for climate sensitivity (1.5 to 4.5 ∘C), we found that (1) a constant emission scenario is virtually certain to overshoot 2 ∘C with a central estimate of 2.0 ∘C by 2100 (4.2 ∘C by 2400). (2) For the present radiative forcing levels it seems unlikely that 2 ∘C are overshoot. (central warming estimate 1.1 ∘C by 2100 and 1.2 ∘C by 2400 with ∼10% probability of overshooting 2 ∘C). However, the risk of overshooting is increasing rapidly if radiative forcing is stabilized much above 400 ppm CO2 equivalence (1.95 W/m2) in the long-term. (3) From a geophysical point of view, if all human-induced emissions were ceased tomorrow, it seems ‘exceptionally unlikely’ that 2 ∘C will be overshoot (central estimate: 0.7 ∘C by 2100; 0.4 ∘C by 2400). (4) Assuming future emissions according to the lower end of published mitigation scenarios (350 ppm CO2eq to 450 ppm CO2eq) provides the central temperature projections are 1.5 to 2.1 ∘C by 2100 (1.5 to 2.0 ∘C by 2400) with a risk of overshooting 2 ∘C between 10 and 50% by 2100 and 1–32% in equilibrium. Furthermore, we quantify the ‘avoidable warming’ to be 0.16–0.26 ∘C for every 100 GtC of avoided CO2 emissions – based on a range of published mitigation scenarios.

Journal ArticleDOI
TL;DR: Within the range of water stress here examined, high yield potential played a preeminent role in the performance of these barley genotypes, explaining why a selection based on minimum yield decrease under stress with respect to favorable conditions failed to identify the best genotypes.
Abstract: Future climate changes are expected to increase risks of drought, which already represent the most common stress factor for stable barley (Hordeum vulgare L.) production in Mediterranean areas. It is important, therefore, to evaluate if there are needs of specific adaptive measures in selecting genotypes for these more stressful environments. Our objective was to study diversity of yield performance under rainfed (R) and irrigated (I) conditions in 89 barley genotypes of different origin, growth habit, and year of release, representing a sample of cultivars grown in Europe. The experiment was conducted at Foggia (southern Italy) for 3 yr. For each trial, a water stress index (WSI) was calculated on the basis of the daily potential and actual evapotranspiration in the growing season, estimated by Thornthwaite's method. The WSI explained most of the variation in yield (R 2 = 0.89**) among years and treatments. We examined, using the yield vs. WSI regression, the behavior of a given genotype across trials. The intercept and slope values were used as measures of yield potential and adaptability under drought, respectively. Several cultivars showing high yield potential and minimal genotype × environment (GE) interaction were identified. Notably, they were characterized by a high slope of the yield vs. WSI regression. Furthermore, within the range of water stress here examined, high yield potential played a preeminent role in the performance of these barley genotypes. This explains why, in this specific context, a selection based on minimum yield decrease under stress with respect to favorable conditions failed to identify the best genotypes.

Journal ArticleDOI
TL;DR: A modelling approach is taken in order to investigate the relationships between the intramolecular distribution of 13C in hexoses and the reactions of primary carbon metabolism, which takes into account C-C bond-breaking reactions of the Calvin cycle and leads to a mathematical expression for the isotope ratios in Hexoses in the steady state.
Abstract: The origin of the non-statistical intramolecular distribution of 13 C in glucose of C3 plants is examined, including the role of the aldolisation of triose phosphates as proposed by Gleixner and Schmidt (1997). A modelling approach is taken in order to investigate the relationships between the intramolecular distribution of 13 C in hexoses and the reactions of primary carbon metabolism. The model takes into account C-C bond-breaking reactions of the Calvin cycle and leads to a mathematical expression for the isotope ratios in hexoses in the steady state. In order to best fit the experimentally-observed intramolecular distribution, the values given by the model indicate that (i), the transketolase reaction fractionates against 13 C by 4-7‰ and (ii), depending on the photorespiration rate used for estimations, the aldolase reaction discriminates in favour of 13 C by 6‰ during fructose-1,6-bisphosphate production; an isotope discrimination by 2‰ against 13 C is obtained when the photorespiration rate is high. Additionally, the estimated fractionations are sensitive to the flux of starch synthesis. Fructose produced from starch breakdown is suggested to be isotopically heavier than sucrose produced in the light, and so the balance between these two sources affects the average intramolecular distribution of glucose derived from stored carbohydrates. The model is also used to estimate photorespiratory and day respiratory fractionations that appear to both depend only weakly on the rate of ribulose-1,5-bisphosphate oxygenation.

Journal ArticleDOI
TL;DR: In this article, a new strategy for the construction of discretizations that are "well-balanced" with respect to dominant hydrostatics is developed, based on the Discrete Archimedes' buoyancy principle.

Journal ArticleDOI
TL;DR: In this paper, a new approach to calculate recurrence plots of multivariate time series, based on joint recurrences in phase space, was proposed, which allows to estimate dynamical invariants of the whole system, like the joint Renyi entropy of second order.

Journal ArticleDOI
TL;DR: In this article, the authors present a guided tour to floods in the Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) and show that large uncertainty is emphasized in the parts dealing with the science of climate change, but in the impact chapters, referring to sectors and regions, growth in flood risk is taken for granted.
Abstract: Recent floods have become more abundant and more destructive than ever in many regions of the globe. Destructive floods observed in the 1990s all over the world have led to record-high material damage, with total losses exceeding one billion US dollars in each of two dozen events. The immediate question emerges as to the extent to which a sensible rise in flood hazard and vulnerability can be linked to climate variability and change. Links between climate change and floods have found extensive coverage in the Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC). Since the material on floods is scattered over many places of two large volumes of the TAR, the present contribution - a guided tour to floods in the IPCC TAR – may help a reader notice the different angles from which floods were considered in the IPCC report. As the water-holding capacity of the atmosphere grows with temperature, the potential for intensive precipitation also increases. Higher and more intense precipitation has been already observed and this trend is expected to increase in the future, warmer world. This is a sufficient condition for flood hazard to increase. Yet there are also other, non-climatic, factors exacerbating flood hazard. According to the IPCC TAR, the analysis of extreme events in both observations and coupled models is underdeveloped. It is interesting that the perception of floods in different parts of the TAR is largely different. Large uncertainty is emphasized in the parts dealing with the science of climate change, but in the impact chapters, referring to sectors and regions, growth in flood risk is taken for granted. Floods have been identified on short lists of key regional concerns.

Journal ArticleDOI
TL;DR: In this article, the role of urbanised territories in the Global Carbon Cycle (GCC) is considered and it is shown that despite the relatively small area of land taken up by urbanized territories (∼2% of total land area), these territories are responsible for ca. 97% of anthropogenic CO2 emissions.

Journal ArticleDOI
TL;DR: In this paper, a multi-scale landscape discretization scheme is presented for large river basins of 10 4 -10 5 km 2 in size, where the landscape is sub-divided into modelling units within a hierarchy of spatial scale levels.

Journal ArticleDOI
TL;DR: In this article, the authors present a possible mechanism which can explain the centennial duration of the 8.2 ka cold event, related to the existence of an additional equilibrium climate state with reduced North Atlantic Deep Water (NADW) formation and a southward shift of the NADW formation area.
Abstract: meltwater pulse is assumed to have a volume of 1.6 10 14 m 3 and a period of discharge of 2 years on the basis of glaciological modeling of the decay of the Laurentide Ice Sheet (LIS). We present a possible mechanism which can explain the centennial duration of the 8.2 ka cold event. The mechanism is related to the existence of an additional equilibrium climate state with reduced North Atlantic Deep Water (NADW) formation and a southward shift of the NADW formation area. Hints at the additional climate state were obtained from the largely varying duration of the pulse-induced cold episode in response to overlaid random freshwater fluctuations in Monte Carlo simulations. The model equilibrium state was attained by releasing a weak multicentury freshwater flux through the St. Lawrence pathway completed by the meltwater pulse. The existence of such a climate mode appears essential for reproducing climate anomalies in close agreement with paleoclimatic reconstructions of the 8.2 ka event. The results furthermore suggest that the temporal evolution of the cold event was partly a matter of chance. INDEX TERMS: 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 4255 Oceanography: General: Numerical modeling; 4532 Oceanography: Physical: General circulation; 4215 Oceanography: General: Climate and interannual variability (3309); 9325 Information Related to Geographic Region: Atlantic Ocean;

Journal ArticleDOI
TL;DR: In this paper, the impact of land-use change on biodiversity is assessed by means of six indicators for three aspects of biodiversity: composition, structure, and function, and the results of the evaluation of the single sub-scenarios were summarized to response functions, which describe the sensitivity of landscape attributes toward landuse changes.

Journal ArticleDOI
TL;DR: In this paper, a model including the temperature feedback predicts that 10% of the fossil fuel CO2 will reside in the atmosphere for longer than 100 ky, and the response of methane clathrate to climate change in the coming century will probably be small, but on longer time scales of 1-10 ky there may be a positive feedback with ocean temperature, amplifying the long-term climate impact of anthropogenic CO2 release.

Journal ArticleDOI
TL;DR: An integrated catchment model and a method with which it is possible to analyse local water table dynamics inside subbasins along with river flow on the regional scale are presented, illustrating the importance of adequate reproduction of the groundwater dynamics in an investigation of a decreasing trend in regional groundwater level.
Abstract: The paper presents an integrated catchment model and a method with which it is possible to analyse local water table dynamics inside subbasins along with river flow on the regional scale. A simple but comprehensive mechanistic groundwater module coupled with the eco-hydrological model SWIM (Soil and Water Integrated Model), which integrates hydrological processes, vegetation, erosion and nutrient dynamics at the watershed scale, was used in the study. The reliability of the model results was tested under well defined boundary conditions by comparing the results with those from a two dimensional numeric groundwater model under steady-state and transient conditions as well as with observed data for two meso-scale basins, using contour maps of the long term mean water table, observed groundwater level data in wells and observed river discharge. Especially in lowland catchments, where the water table is relatively shallow, the dynamics of river discharge are mainly influenced by changes in groundwater contribution to river flow. However, a correct reproduction of river discharge by hydrological models does not guarantee the adequacy of simulated spatio-temporal dynamics of soil moisture, water fluxes and groundwater in the basin. But even though the primary purpose of distributed hydrological models is to reproduce river discharge and water fluxes in the entire catchment, they are often validated using only the observed river discharge at the basin outlet for comparisons. The additional use of groundwater observations for model validation can serve as a measure to overcome the problem. The study area is located in the lowland part of the Elbe river basin, which is representative for semi-humid landscapes in Europe, where water availability during the summer season is the main limiting factor for plant growth and crop yields. The importance of adequate reproduction of the groundwater dynamics is illustrated in an investigation of a decreasing trend in regional groundwater level.

Journal ArticleDOI
TL;DR: In this article, the authors evaluate a viable tool for the potential predictability of dry and wet spells using principal component analysis (PCA) and find that periodicities ranging from 3.4 to 12 years characterise the SPI signals in both regions and essentially drive the main dry or wet occurrences.
Abstract: The purpose of this paper is to evaluate a viable tool for the potential predictability of dry and wet spells. We select two regions in Europe that have distinct precipitation regimes: Sicily and Elbe basin (Germany). The analysis of dryness and wetness in these regions from 1951 to 2000 is based on the Standardized Precipitation Index (SPI) computed on a long-time scale (two years) and the evaluation of their time-space variability is carried out using Principal Component Analysis. Results suggest that periodicities ranging from 3.4 to 12 years characterise the SPI signals in both regions and essentially drive the main dry and wet occurrences. In Sicily, at variance with the Elbe basin, superimposed to this variability there is also a clearly detectable linear trend that is perhaps related to long-term periodicity. Moreover, the shift in phase found between the common periods implies that often on the longer time scale if the Elbe region has dry conditions, Sicily is wet and viceversa. The reconstruction of the SPI time series by considering the periodicity that greatly contribute to the total power spectrum variance gives good results and provides good opportunities for predictability.

Journal ArticleDOI
TL;DR: The potential impacts of changes in precipitation patterns associated with global climate change on the relationship between soil community diversity and litter decomposition were investigated in this article, where two decomposer communities in litterbags (1000 and 45 mum mesh size) containing spruce litter were subjected to two irrigation treatments: constant and fluctuating (drying/rewetting) moisture conditions.
Abstract: The potential impacts of changes in precipitation patterns associated with global climate change on the relationship between soil community diversity and litter decomposition were investigated. For a period of ca. 5 months, two decomposer communities in litterbags (1000 and 45 mum mesh size) containing spruce litter were subjected to two irrigation treatments: constant and fluctuating (drying/rewetting) moisture conditions. The latter were expected to induce moisture stress on the decomposer communities. The two mesh sizes were used to exclude different faunal components from the decomposer communities. The 1000 mum mesh excluded only the macrofauna, whereas the 45 mum mesh excluded both the macro- and mesofauna. In the short-term perspective of the present study, mesofauna abundance showed no response to imposed fluctuating moisture conditions. Irrespective of the presence of mesofauna, mass loss, microbial biomass and the control mechanisms, regulating carbon mineralization appeared unaffected by fluctuating moisture conditions. The reduction in the functional/structural diversity of the decomposer communities in the 45 mum litterbags resulted in strongly increased Nematoda abundance but it did not alter the response of Nematoda to fluctuating moisture conditions. Processes in the nitrogen (N)-cycle and mass loss were sensitive indicators of changes in the structural and functional complexity of decomposer communities. However, a negative effect of fluctuating moisture conditions on extractable N was coupled to the presence of mesofauna. Extremes in rainfall patterns, generated by climate change, may have a negative impact on the availability of nutrients, particularly N, for plants. This effect could be amplified by an additional impoverishment in the structural and functional complexity of the respective decomposer communities.

Journal ArticleDOI
TL;DR: A prominent new example is a paper by Shaviv and Veizer as mentioned in this paper, which claims that fluctuations in cosmic ray flux reaching the Earth can explain 66% of the temperature variance over the past 520 m.y.
Abstract: Several recent papers have applied correlation analysis to climate-related time series in the hope of finding evidence for causal relationships. For a critical discussion of correlations between solar variability, cosmic rays, and cloud cover, see Laut [2003]. A prominent new example is a paper by Shaviv and Veizer [2003], which claims that fluctuations in cosmic ray flux reaching the Earth can explain 66% of the temperature variance over the past 520 m.y.,and that the sensitivity of climate to a doubling of CO2 is less than previously estimated.

Journal ArticleDOI
TL;DR: In this paper, the chemical structures of the polymers were confirmed by IR, 1H and 13C NMR, and elemental analysis, and the final morphologies were determined by molecular characteristics (side chains volume fraction, backbone stiffness) of the studied polymers.
Abstract: Alkoxy-substituted CN-containing phenylene−vinylene−alt-phenylene−ethynylene hybrid polymers (CN−PPV−PPE), 3a, 3b, and 7a, were obtained from luminophoric dialdehydes 1 by step growth polymerization via Knoevenagel reaction as high molecular-weight materials. Corresponding CN-free polymers 3c and 7b and an ethynylene-free polymer 5 with similar side chains were synthesized for the purpose of comparison. The chemical structures of the polymers were confirmed by IR, 1H and 13C NMR, and elemental analysis. Thermal characterization was conducted by means of thermogravimetric analysis and differential scanning calorimetry. Morphology was investigated by means of optical microscopy and small-angle light scattering. The final morphologies are determined by the molecular characteristics (side chains volume fraction, backbone stiffness) of the studied polymers. All the CN-containing polymers 3b, 5, and 7a exhibit higher fluorescence quantum yield in solid state (50 to 60%), but lower quantum yields (12−40%) in dil...

Journal ArticleDOI
TL;DR: In this article, a series of simulations with a coupled ocean-atmosphere model of intermediate complexity, CLIMBER-2, using a reduced solar constant of 6% and varied CO2 concentrations was conducted to simulate the climatic conditions of the Neoproterozoic.
Abstract: In order to simulate the climatic conditions of the Neoproterozoic, we have conducted a series of simulations with a coupled ocean–atmosphere model of intermediate complexity, CLIMBER-2, using a reduced solar constant of 6% and varied CO2 concentrations. We have also tested the impact of the breakup of the supercontinent Rodinia that has been hypothesized to play an important role in the initiation of an ice-covered Earth. Our results show that for the critical values of 89 and 149 ppm of atmospheric CO2, a snowball Earth occurs in the supercontinent case and in the dislocated configuration, respectively. The study of the sensitivity of the meridional oceanic energy transport to reductions in CO2 concentration and to the dislocation of the supercontinent demonstrates that dynamics ocean processes can modulate the CO2 threshold value, below which a snowball solution is found, but cannot prevent it. The collapse of the overturning cells and of the oceanic heat transport is mainly due to the reduced zonal temperature gradient once the sea-ice line reaches the 30° latitudinal band but also to the freshening of the tropical ocean by sea-ice melt. In term of feedbacks, the meridional atmospheric heat transport via the Hadley circulation plays the major role, all along the CO2 decrease, by increasing the energy brought in the front of the sea-ice margin but does not appear enough efficient to prevent the onset of the sea-ice-albedo instability in the case of the continental configurations tested in this contribution.

Journal ArticleDOI
TL;DR: In this article, the authors apply a pseudo-spectral method where waves are created and superimposed within a limited wavenumber interval, and find that small disturbances are found to have a large impact on the dust forming system.
Abstract: Dust formation in brown dwarf atmospheres is studied by utilising a model for driven turbulence in the mesoscopic scale regime. We apply a pseudo-spectral method where waves are created and superimposed within a limited wavenumber interval. The turbulent kinetic energy distribution follows the Kolmogoroff spectrum which is assumed to be the most likely value. Such superimposed, stochastic waves may occur in a convectively active environment. They cause nucleation fronts and nucleation events and thereby initiate the dust formation process which continues until all condensible material is consumed. Small disturbances are found to have a large impact on the dust forming system. An initially dust-hostile region, which may originally be optically thin, becomes optically thick in a patchy-way showing considerable variations in the dust properties during the formation process. The dust appears in lanes and curls as a result of the interaction with waves, i.e. turbulence, which form larger and larger structures with time. Aiming at a physical understanding of the variability of brown dwarfs, related to structure formation in substellar atmospheres, we work out first necessary criteria for small-scale closure models to be applied in macroscopic simulations of dust-forming astrophysical systems.