Showing papers by "Potsdam Institute for Climate Impact Research published in 1996"

A bioclimatic model for the potential distributions of North European tree species under present and future climates

Abstract: A bioclimatic model based on physiological constraints to plant growth and regeneration is used here in an empirical way to describe the present natural distributions of northern Europe's major trees. Bioclimatic variables were computed from monthly means of temperature, precipitation and sunshine (%) interpolated to a 10' grid taking into account elevation. Minimum values of mean coldest-month temperature (T c ) and 'effective' growing degree days (GDD*) were fitted to species' range limits. GDD* is total annual growing degree days (GDD) minus GDD to budburst (GDD°). Each species was assigned to one of the chilling-response categories identified by Murray, Cannell & Smith (1989) to calculate GDD°. Maximum T c values were fitted to continental species' mild-winter limits and other deciduous species' warm-winter limits. Minimum values of relative growing-season moisture availability (α*) were estimated from silvics. Growth indices were calculated based on potential net assimilation (a quadratic in daily temperature) and α*. Growth can be rapid near a range limit, e.g. Picea abies (L.) Karsten in southern Sweden. Climate changes expected for CO 2 doubling were projected on to the grid. Simulated distribution changes reflected interspecific differences in response to changing seasonality. Chilling responses proved important, e.g. the predicted range limit of Fagus sylvatica L. contracts in the west while expanding northwards as winters warm more than summers. Transient responses to climate change can be modelled using the same information provided that fundamental and realized niche limitations are distinguished-a caveat that underlines the dearth of experimental information on the climatic requirements for growth, and especially regeneration, of many important trees.

Plant functional types and climatic change: Introduction

Abstract: . Plant functional types are a necessary device for reducing the complex and often uncharted characteristics of species diversity in function and structure when attempting to project the nature and function of species assemblages into future environments. A workshop was held to review the current methods commonly used for defining plant functional types, either globally or for particular biomes, and to compare them with the field experiences of specialists for specific biomes of the world. The methods fall into either an objective and inductive approach or a subjective and deductive approach. When the different methods were tested, it was generally found that the classification for one site or environment was not wholly applicable to a different site or environment. However, the degree of change which is necessary for adjustment between environments may not prove to be a major limitation in the use of functional types.

Third generation oral contraceptives and risk of myocardial infarction: an international case-control study

Abstract: Objective: To test whether use of combined oral contraceptives containing third generation progestogens is associated with altered risk of myocardial infarction. Design: Matched case-control study. Setting: 16 centres in Austria, France, Germany, Switzerland, and the United Kingdom. Subjects: Cases were 153 women aged 16-44 with a myocardial infarction event. Controls were 498 women (at least 3 controls per case) unaffected by myocardial infarction who were matched with their corresponding case for age and for hospital or community setting within four months of the index infarction. Main outcome measures: Odds ratios derived with stratified analyses and unconditional logistic regression to adjust for potential confounding variables. Results: The estimated odds ratio for myocardial infarction of third compared with second generation oral contraceptives among all 651 study subjects was 0.36 (95% confidence interval 0.1 to 1.2) (P=0.11). The odds ratio for the United Kingdom and Germany alone was 0.45 (0.1 to 1.8) (P=0.26). Other odds ratios for the five countries were 3.1 (1.5 to 6.3) (P=0.003) for use of second generation products v no current use and 1.1 (0.4 to 3.4) (P=0.9) for use of third generation products v no current use. Among the confounding variables the independent contribution of smoking (for which adjustment was made in the above estimates) proved to be important (10.1 (5.7 to 17.9), P Conclusion: An odds ratio of 0.45 with wide confidence intervals shows that third generation oral contraceptives compared with second generation products are associated with a reduced risk of myocardial infarction or with no difference. This finding from an interim analysis should be interpreted with extreme caution. However, the excess risk of venous thromboembolism associated with the use of third generation products may be balanced by the reduced risk of myocardial infarction associated with the same products. Key messages Key messages Compared with the results of British studies published in the 1970s, the risk of myocardial infarction among current users v non-users of second generation oral contraceptives was low The risk of myocardial infarction was appreciably lower among women using third generation products, the risk being comparable to that among women who did not use oral contraception and two to three times lower than that among women using second generation products The results suggest that about 12 fewer deaths from myocardial infarction in England and Wales and 46 fewer in Germany would occur each year if all those taking second generation oral contraceptives started taking third generation products Both the risks and the benefits of oral contraceptives need to be considered in a balanced way so that doctors can give judicious advice and women have informed choice

A comparison of forest gap models : Model structure and behaviour

Abstract: Forest gap models share a common structure for simulating tree population dynamics, and many models contain the same or quite similar ecological factors. However, a wide variety of formulations are being used to implement this general structure. The comparison of models incorporating different formulations is important for model validation, for assessing the reliability of model projections obtained under scenarios of climatic change, and for the development of models with a wide range of applicability. This paper reviews qualitative and quantitative comparisons of the structure and behaviour of forest gap models.

Functional types of trees in temperate and boreal forests: classification and testing

Abstract: . Impacts of climatic change on ecosystems over large areas cannot usually be assessed on a species basis. The definition of plant functional types (PFTs) may make this task feasible, but its potential and limitations need to be evaluated carefully by quantitative tests. This paper presents such a method for testing a hypothesis about PFTs. A deductive approach is used to elaborate a functional classification of temperate and boreal trees based on their response to climatic change and their feedbacks to the climate system using four attributes: (1) evergreen/deciduous; (2) cold tolerance; (3) drought tolerance; (4) shade tolerance. These attributes are combined to yield six PFTs. The classification is tested by implementing the six PFTs in the forest gap model ForClim, and the behaviour of the PFT-based model is compared to species-based simulation results in Europe and in eastern North America. The six PFTs provide an accurate description of both the physiognomy and the composition of European forests in both transient and equilibrium phases. Under the IPCC ‘Business- As-Usual’ scenario of climatic change for southern and central Europe, some differences in the forest composition are simulated, pointing at the need of testing PFT schemes not only under current, but also under hypothesized future climates. For eastern North America it was necessary to estimate the parameters characterizing the six PFTs anew. When this was done, the PFT-based simulation yielded results paralleling those of the species-based model closely. The potential and limitations of the present classification are discussed. It is concluded that deficiencies in current gap models, but probably also different evolutionary pathways in North America as compared to Europe, are responsible for the different parameterizations on the two continents.

Global vegetation models: incorporating transient changes to structure and composition

Abstract: . We describe an approach for developing a Dynamic Global Vegetation Model (DGVM) that accounts for transient changes in vegetation distribution over a decadal time scale. The DGVM structure is based on a linkage between an equilibrium global vegetation model and smaller scale ecosystem dynamics modules that simulate the rate of vegetation change. Vegetation change is classified into four basic types, based largely on the projected change in above-ground biomass of the vegetation. These four types of change are: (1) dieback of forest, shrubland or grassland; (2) successional replacement within forest, shrubland or grassland; (3) invasion of forest, shrubland or grassland; (4) change in tree/grass ratio. We then propose an approach in which the appropriate ecosystem dynamics module for each type of change is applied and the grid cells of the global model updated accordingly. An approach for accounting for fire, as an example of a disturbance which may strongly influence the rate and spatial pattern of forest dieback, is incorporated. We also discuss data needs for the development, calibration and validation of the model.

Could preferential prescribing and referral behaviour of physicians explain the elevated thrombosis risk found to be associated with third generation oral contraceptives

Abstract: BACKGROUND Recently published case-control studies on third versus second generation oral contraceptives showed a slightly increased risk for venous thromboembolism (VTE) and led to a discussion about biases or confounders external to the study such as, preferential prescribing of third generation pills to women at higher risk and differential diagnostic behaviour. METHODS An interview survey with 102 physicians was performed in 2 weeks of December 1995 in Germany and 1209 of their patients were included in a retrospective cohort analysis of drug utilization and risk markers. RESULTS German physicians previously preferred to prescribe third generation pills whenever an increased risk was perceived, i.e. risk for VTE and for arterial thrombosis (risk factors, personal or family history of cardiovascular diseases). Almost all predefined risk scenarios were associated with an increased attention to non-specific venous symptoms and patients were more frequently sent for intensive diagnostic search for venous thromboses. The behaviour was not directly dependent on the type of OC; however the third generation pills were indirectly associated with higher risk in the pill-taking women. The physicians' view was confirmed by the analysis of the cohorts of patients: preferential prescribing was also found in this data set, although it was not as impressive as in the physicians responses. CONCLUSION The possibility cannot be excluded that preferential prescribing and differential diagnostic behaviour alone could have explained the roughly two-fold increased odds ratios from case-control studies recently published, had this information been available among the study variables.

Development of a Fuzzy optimization model, supporting global warming decision-making

Abstract: An increasing number of models have been developed to support global warming response policies The model constructors are facing a lot of uncertainties which limit the evidence of these models The support of climate policy decision-making is only possible in a semi-quantitative way, as presented by aFuzzy model The model design is based on an optimization approach, integrated in a bounded risk decision-making framework Given some regional emission-related and impact-related restrictions, optimal emission paths can be calculated The focus is not only on carbon dioxide but on other greenhouse gases too In the paper, the components of the model will be described Cost coefficients, emission boundaries and impact boundaries are represented asFuzzy parameters TheFuzzy model will be transformed into a computational one by using an approach of Rommelfanger In the second part, some problems of applying the model to computations will be discussed This includes discussions on the data situation and the presentation, as well as interpretation of results of sensitivity analyses The advantage of theFuzzy approach is that the requirements regarding data precision are not so strong Hence, the effort for data acquisition can be reduced and computations can be started earlier

Integrated scenarios of acidification and climate change in Asia and Europe

Abstract: Two integrated assessment models, one for climate change on a global scale (IMAGE 2) and another for the regional analysis of the impacts of acidifying deposition (RAINS), have been linked to assess the impacts of reducing sulphur emission on ecosystems in Asia and Europe. While such reductions have the beneficial effect of reducing the deposition of acidifying compounds and thus the exceedance of critical loads of ecosystems, they also reduce the global level of sulphate aerosols and thus enhance the impact of increased emissions of greenhouse gases, and consequently increase the risk of potential vegetation changes. The calculations indicate that about 70% of the ecosystems in Asia would be affected by either acid deposition or climate change in the year 2100 (up from 20% in 1990) for both sulphur emission scenarios (controlled and uncontrolled), whereas in Europe the impacted area would remain at a level of about 50%, with a dip early next century. More generally, the effects of reducing sulphur emissions and thus enhancing climate change would about balance for the Asian region, whereas for Europe the desirable impact of sulphur emission reductions would greatly outweigh its undesirable effects.

Long-term survival after myocardial infarction: relationship with thrombolysis and discharge medication Results of the Augsburg Myocardial Infarction Follow-up Study 1985 to 1993

Abstract: A large number of randomized clinical trails have shown that thrombolysis, long-term treatment with beta-blockers, antiplatelet drugs, and angiotensin converting enzyme inhibitors improve survival after acute myocardial infarction (AMI). However, for calcium channel blockers (nifedipine, diltiazem, and verapamil) there was either no benefit, or positive effects have been reported in subgroups only. Recent studies have raised concern about the safety of this drug class, especially in patients with coronary heart disease. We studied the long-term survival, for a median follow-up time of 4·4 years, of 1197 non-diabetic patients in the population-based AMI registry in Augsburg, Germany, aged 25–74 years, who had survived a first Q wave acute myocardial infarction for at least 28 days. The impact of thrombolysis and prescribed medication at discharge (beta-blockers, antiplatelet drugs, and calcium channel blockers) on long-term survival was analysed using the Cox-Proportional-Hazard model, controlling for age, sex, and concomitant cardiac drug use. Thrombolysis (risk ratio, RR, 0–72; 95% confidence interval, CI, 0.48–1·08), long-term beta-blockade (RR 0·52; 95%Cl 0·36–0·74) and antiplatelet drug use (RR 0·69; 95%Cl 0·50–0·94) were associated with considerable reductions in total mortality. The use of calcium channel blockers was not associated with a reduction in total mortality (RR 1·23; 95%Cl 0·89–1·69). Separate analyses for nifedipine (RR 1·00; 95%Cl 0·68–1·48), and diltiazem (RR 1·55; 95%Cl 1·04–2·32) showed an increased risk of death associated with the latter. Using patients on beta-blockers only (RR 1·00) as a reference, the prescription of these calcium channel blockers was consistently associated with an increased total mortality (nifedipine, without beta-blockers RR 1·20; 95%Cl 1·12–3·57, diltiazem, without beta-blockers RR 2·87; 95%Cl 1·75–4·70). These results from an observational study demonstrate a benefit of thrombolysis, beta-adrenergic blockade and antiplatelet drug use on long-term survival in acute myocardial infarction patients. Calcium channel blocker use appears to be associated with an increased risk of death. These data support the need for controlled trials to address this issue specifically.

Simulating forest dynamics in a complex topography using gridded climatic data

Abstract: The forest model ForClim was used to evaluate the applicability of gap models in complex topography when the climatic input data is provided by a global database of 0.5° resolution. The analysis was based on 12 grid cells along an altitudinal gradient in the European Alps. Forest dynamics were studied both under current climate as well as under four prescribed 2 × CO2 scenarios of climatic change obtained from General Circulation Models, which allowed to assess the sensitivity of mountainous forests to climatic change.

Application of a forest succession model to a continentality gradient through Central Europe

Abstract: The forest succession model FORSKA was applied to a west-east transect across Central Europe using points from a global climate data set. Climate change experiments were undertaken for two general circulation model scenarios and two different site classes. The simulated climate changes lead to reduced forest productivity and a changed species composition on most sites. Under current climate, the broad scale pattern of the climatically driven distribution of forest communities is quite realistically reproduced. However, the resolution of climate data imposes limitations on the simulation of forest dynamics in subcontinental climate, because climate variability and extreme events are not well represented.

Interim review of the Transnational Case-control Study of Oral Contraceptives and Health: approved protocol revisions through September 1995.

Abstract: UNLABELLED The protocol of the Transnational Study on Oral Contraceptives has been published at the outset of the study in order to ensure the correct performance of the study and to ensure the study's scientific integrity. Potential revisions and additions to this protocol had been announced in the prior publication. This article focuses on those points of protocol which have been resolved as practical experience was gathered as well as additional modifications required by practical and scientific considerations. The major alterations are based on exposure prevalences in controls and on power calculations. The low (1.8%) exposure to gestodene among German controls led to the discontinuation of the German component and to the accelerated accession in additional countries. THE CASE control ratio was altered to 3:1 for purposes of economy based on power calculations. Numerous minor points, most addressed in the prior protocol, have been resolved. It is found that these modifications of the study protocol do not impair the study's conduct, its scientific integrity, nor its capability of providing answers to the study question.

Transboundary environmental problems and new trade rules

Abstract: Increased environmental pollution and the globalization of economies have initiated an academic debate on the relationship between international trade and the environment. Addresses the question of whether the present GATT/WTO regime conflicts with effective policies to cope with transboundary environmental problems, including the protection of global commons. Analyses the welfare effects of transboundary pollution tariffs by using a simple partial equilibrium framework. Contrasts the results with an assessment of the existing GATT/WTO regime, in which no distinction between national and transboundary environmental problems has been made. Outlines, in conclusion, some basic elements of a necessary reform of the GATT/WTO regime. These proposals would allow border tax adjustment for certain types of production‐related environmental charge without undermining an open and non‐discriminatory multilateral trading system.

Grid point surface air temperature calculations with a fast turnaround: Combining the results of IMAGE and a GCM

Abstract: This paper describes a methodology that combines the outputs of (1) the Integrated Model to Assess the Greenhouse Effect (IMAGE Version 1.0) of the Netherlands National Institute of Public Health and Environmental Protection (RIVM) (given a greenhouse gas emission policy, this model can estimate the effects such as global mean surface air temperature change for a wide variety of policies) and (2) ECHAM-1/LSG, the Global Circulation Model (GCM) of the Max-Planck Institute for Meteorology in Hamburg, Germany. The combination enables one to calculate grid point surface air temperature changes for different scenarios with a turnaround time that is much quicker than that for a GCM. The methodology is based upon a geographical pattern of the ratio of grid point temperature change to global mean values during a certain period of the simulation, as calculated by ECHAM-1/LSG for the 1990 Scenarios A and D of the Intergovernmental Panel on Climate Change (IPCC). A procedure, based upon signal-to noise ratios in the outputs, enabled us to estimate where we have confidence in the methodology; this is at about 23% to 83% of the total of 2,048 grid points, depending upon the scenario and the decade in the simulation. It was found that the methodology enabled IMAGE to provide useful estimates of the GCM-predicted grid point temperature changes. These estimates were within 0.5K (0.25K) throughout the 100 years of a given simulation for at least 79% (74%) of the grid points where we are confident in applying the methodology. The temperature ratio pattern from Scenario A enabled IMAGE to provide useful estimates of temperature change within 0.5K (0.25K) in Scenario D for at least 88% (68%) of the grid points where we have confidence; indicating that the methodology is transferable to other scenarios. Tests with the Geophysical Fluid Dynamics Laboratory GCM indicated, however, that a temperature ratio pattern may have to be developed for each GCM. The methodology, using a temperature ratio pattern from the 1990 IPCC Scenario A and involving IMAGE, gave gridded surface air temperature patterns for the 1992 IPCC radiative-forcing Scenarios C and E and the RIVM emission Scenario B; none of these scenarios has been simulated by ECHAM-1/LSG. The simulations reflect the uncertainty range of a future warming.

Calcite formation in microbial mats: modeling and quantification of inhomogeneous distribution patterns by a cellular automaton model and multifractal measures

Abstract: The evolution of early diagenetic calcite cements in microbial mats of recent supratidal sediments of the southern North Sea is modeled in a two-dimensional microscale approach by a cellular automaton model (CAM). Calcite is traced out in the model by virtual calcium distribution patterns obtained from runs under different assumptions concerning sediment-intrinsic conditions. For justification of the CAM, real calcium distribution patterns, documented by scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDX), are quantitatively compared with the virtual patterns on the basis of multifractal analyses. The formation of high magnesian calcite as a consequence of biogenic anaerobic decomposition of organic matter starts at certain initial calcite domains. In this stage an inhomogeneous and multifractal calcium distribution is characteristic. Nearly complete remineralization of organic matter leads to monofractal behavior of generalized fractal dimensions (DB(q) ±1.84). The CAM results confirm that calcite formation is a self-determining morphogenetical process and diffusive transport processes of reactants within the mat affect the biogenic calcite formation.