Showing papers by "Potsdam Institute for Climate Impact Research published in 1998"

Climate Change and Forest Fire Potential in Russian and Canadian Boreal Forests

Abstract: In this study outputs from four current General Circulation Models (GCMs) were used to project forest fire danger levels in Canada and Russia under a warmer climate. Temperature and precipitation anomalies between 1 × CO2 and 2 × CO2 runs were combined with baseline observed weather data for both countries for the 1980–1989 period. Forecast seasonal fire weather severity was similar for the four GCMs, indicating large increases in the areal extent of extreme fire danger in both countries under a 2 × CO2 climate scenario. A monthly analysis, using the Canadian GCM, showed an earlier start to the fire season, and significant increases in the area experiencing high to extreme fire danger in both Canada and Russia, particularly during June and July. Climate change as forecast has serious implications for forest fire management in both countries. More severe fire weather, coupled with continued economic constraints and downsizing, mean more fire activity in the future is a virtual certainty. The likely response will be a restructuring of protection priorities to support more intensive protection of smaller, high-value areas, and a return to natural fire regimes over larger areas of both Canada and Russia, with resultant significant impacts on the carbon budget.

Indication of a Universal Persistence Law Governing Atmospheric Variability

Abstract: We study the temporal correlations in the atmospheric variability by 14 meteorological stations around the globe, the variations of the daily maximum temperatures from their average values. We apply several methods that can systematically overcome possible nonstationarities in the data. We find that the persistence, characterized by the correlation C(s) of temperature variations separated by s days, approximately decays $C(s)\ensuremath{\sim}{s}^{\ensuremath{-}\ensuremath{\gamma}}$, with roughly the same exponent $\ensuremath{\gamma}\ensuremath{\cong}0.7$ for all stations considered. The range of this universal persistence law seems to exceed one decade, and is possibly even larger than the range of the temperature series considered.

Simulation of modern and glacial climates with a coupled global model of intermediate complexity

Abstract: A global coupled ocean–atmosphere model of intermediate complexity is used to simulate the equilibrium climate of both today and the Last Glacial Maximum, around 21,000 years ago. The model successfully predicts the atmospheric and oceanic circulations, temperature distribution, hydrological cycle and sea-ice cover of both periods without using ‘flux adjustments’. Changes in oceanic circulation, particularly in the Atlantic Ocean, play an important role in glacial cooling.

The Influence of Vegetation-Atmosphere-Ocean Interaction on Climate During the Mid-Holocene

Abstract: Simulations with a synchronously coupled atmosphere-ocean-vegetation model show that changes in vegetation cover during the mid-Holocene, some 6000 years ago, modify and amplify the climate system response to an enhanced seasonal cycle of solar insolation in the Northern Hemisphere both directly (primarily through the changes in surface albedo) and indirectly (through changes in oceanic temperature, sea-ice cover, and oceanic circulation). The model results indicate strong synergistic effects of changes in vegetation cover, ocean temperature, and sea ice at boreal latitudes, but in the subtropics, the atmosphere-vegetation feedback is most important. Moreover, a reduction of the thermohaline circulation in the Atlantic Ocean leads to a warming of the Southern Hemisphere.

Association of Inhaled Corticosteroid Use With Cataract Extraction in Elderly Patients

Abstract: Context.—The use of systemic corticosteroids is a known risk factor for the development of cataracts.Objective.—To determine whether treatment with inhaled corticosteroids is associated with cataract extraction in the elderly.Design.—Case-control study.Setting.—Quebec universal health insurance program for all elderly (provincial health insurance plan database [RAMQ database]).Patients.—RAMQ enrollees 70 years and older. The 3677 cases were patients with a cataract extraction between 1992 and 1994. The 21868 controls were randomly selected from patients who did not have a diagnosis of cataract and matched to cases on the index date of the case.Main Outcome Measures.—Odds ratio of cataract extraction in patients with prolonged cumulative exposure to inhaled corticosteroids compared with nonusers.Results.—Excluding patients with systemic steroid treatment and after adjusting for age, sex, diabetes, systemic hypertension, glaucoma, ophthalmic steroids, and the number of physician claims for services, use of inhaled corticosteroids for more than 3 years was associated with undergoing cataract extraction (odds ratio [OR], 3.06; 95% confidence interval [CI], 1.53-6.13). For high average daily doses of beclomethasone or budesonide (>1 mg), the OR was elevated after more than 2 years of treatment (OR, 3.40; 95% CI, 1.49-7.76), whereas for low to medium doses (≤1 mg) of these drugs, the OR was 1.63 (95% CI, 0.85-3.13) after 2 years.Conclusion.—Prolonged administration of high doses of inhaled corticosteroids increases the likelihood of undergoing cataract extraction in elderly patients. Further studies are needed to investigate the risk of developing cataracts for low to medium doses over longer periods.

Evaluation of terrestrial carbon cycle models through simulations of the seasonal cycle of atmospheric CO2: First results of a model intercomparison study

Abstract: Results of an intercomparison among terrestrial biogeochemical models (TBMs) are reported, in which one diagnostic and five prognostic models have been run with the same long-term climate forcing. Monthly fields of net ecosystem production (NEP), which is the difference between net primary production (NPP) and heterotrophic respiration RH, at 0.5° resolution have been generated for the terrestrial biosphere. The monthly estimates of NEP in conjunction with seasonal CO2 flux fields generated by the seasonal Hamburg Model of the Oceanic Carbon Cycle (HAMOCC3) and fossil fuel source fields were subsequently coupled to the three-dimensional atmospheric tracer transport model TM2 forced by observed winds. The resulting simulated seasonal signal of the atmospheric CO2 concentration extracted at the grid cells corresponding to the locations of 27 background monitoring stations of the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory network is compared with measurements from these sites. The Simple Diagnostic Biosphere Model (SDBM1), which is tuned to the atmospheric CO2 concentration at five monitoring stations in the northern hemisphere, successfully reproduced the seasonal signal of CO2 at the other monitoring stations. The SDBM1 simulations confirm that the north-south gradient in the amplitude of the atmospheric CO2 signal results from the greater northern hemisphere land area and the more pronounced seasonality of radiation and temperature in higher latitudes. In southern latitudes, ocean-atmosphere gas exchange plays an important role in determining the seasonal signal of CO2. Most of the five prognostic models (i.e., models driven by climatic inputs) included in the intercomparison predict in the northern hemisphere a reasonably accurate seasonal cycle in terms of amplitude and, to some extent, also with respect to phase. In the tropics, however, the prognostic models generally tend to overpredict the net seasonal exchanges and stronger seasonal cycles than indicated by the diagnostic model and by observations. The differences from the observed seasonal signal of CO2 may be caused by shortcomings in the phenology algorithms of the prognostic models or by not properly considering the effects of land use and vegetation fires on CO2 fluxes between the atmosphere and terrestrial biosphere.

On multiple solutions of the atmosphere–vegetation system in present‐day climate

Abstract: An asynchronously coupled global atmosphere–biome model is used to assess the stability of the atmosphere–vegetation system under present-day conditions of solar irradiation and sea-surface temperatures. When initialized with different land-surface conditions (1, the continents, except for regions of inland ice, completely covered with forest; 2, with grassland; 3, with (dark) desert; and 4, with (bright) sand desert), the atmosphere–biome model finds two equilibrium solutions: the first solution yields the present-day distribution of subtropical deserts, the second reveals a moister climate in North Africa and Central East Asia and thereby a northward shift of vegetation particularly in the south-western Sahara. The first solution is obtained with initial condition 4, and the second with 1, 2, 3. When comparing these results with an earlier study of biogeophysical feedback in the African and Asian monsoon area, it can be concluded that North Africa is probably the region on Earth which is most sensitive considering bifurcations of the atmosphere–vegetation system at the global scale.

Photosynthesis and conductance of spring‐wheat leaves: field response to continuous free‐air atmospheric CO2 enrichment

Abstract: Spring wheat was grown from emergence to grain maturity in two partial pressures of CO2 (pCO2): ambient air of nominally 37 Pa and air enriched with CO2 to 55 Pa using a free-air CO2 enrichment (FACE) apparatus. This experiment was the first of its kind to be conducted within a cereal field without the modifications or disturbance of microclimate and rooting environment that accompanied previous studies. It provided a unique opportunity to examine the hypothesis that continuous exposure of wheat to elevated pCO2 will lead to acclimatory loss of photosynthetic capacity. The diurnal courses of photosynthesis and conductance for upper canopy leaves were followed throughout the development of the crop and compared to model-predicted rates of photosynthesis. The seasonal average of midday photosynthesis rates was 28% greater in plants exposed to elevated pCO2 than in contols and the seasonal average of the daily integrals of photosynthesis was 21% greater in elevated pCO2 than in ambient air. The mean conductance at midday was reduced by 36%. The observed enhancement of photosynthesis in elevated pCO2 agreed closely with that predicted from a mechanistic biochemical model that assumed no acclimation of photosynthetic capacity. Measured values fell below predicted only in the flag leaves in the mid afternoon before the onset of grain-filling and over the whole diurnal course at the end of grain-filling. The loss of enhancement at this final stage was attributed to the earlier senescence of flag leaves in elevated pCO2. In contrast to some controlled-environment and field-enclosure studies, this field-scale study of wheat using free-air CO2 enrichment found little evidence of acclimatory loss of photosynthetic capacity with growth in elevated pCO2 and a significant and substantial increase in leaf photosynthesis throughout the life of the crop.

Integrated environmental assessment methods: Evolution and applications

Abstract: The central objectives of the European Forum on Integrated Environmental Assessment (EFIEA) include improving the scientific quality of Integrated Environmental Assessments (IEA) as well as strengthening the interactions between science and policy making in environmental matters This paper is intended to provide a concise assessment of the evolution of IEA methods and present it as a background to current thinking on and practice in IEA Historical roots of IEA concepts and applications are explored Common elements and distinctive features in recent proposals to define IEA are sorted and a liberal definition is proposed for the purposes of the present methodological study This definition emphasizes the interdisciplinary character and environmental policy orientation of IEAs Changes in the nature, social perception, and management of environmental problems are identified as the major factors driving methodological development in IEAs A simple scheme is proposed to arrange the main elements of IEA: disciplinary tools, integration tools, and assessment frameworks The role of IEAs in environmental management is examined by adopting the concept of risk management functions Due to the varying needs for interdisciplinary research and diverging degrees of policy involvement across those functions, the potential contribution of IEAs to activities belonging to different functions also varies The flexibility and diversity of IEAs are demonstrated by a sampler of frameworks that have been developed to address profoundly different problems and audiences

Modelling global terrestrial vegetation–climate interaction

Abstract: By coupling an atmospheric general circulation model asynchronously with an equilibrium vegetation model, manifold equilibrium solutions of the atmosphere–biosphere system have been explored. It is found that under present–day conditions of the Earth's orbital parameters and sea–surface temperatures, two stable equilibria of vegetation patterns are possible: one corresponding to present–day sparse vegetation in the Sahel, the second solution yielding savannah which extends far into the south–western part of the Sahara. A similar picture is obtained for conditions during the last glacial maximum (21 000 years before present (BP)). For the mid–Holocene (6000 years BP), however, the model finds only one solution: the green Sahara. We suggest that this intransitive behaviour of the atmosphere–biosphere is related to a westward shift of the Hadley–Walker circulation. A conceptual model of atmosphere–vegetation dynamics is used to interpret the bifurcation as well as its change in terms of stability theory.

Influence of Mediterranean Outflow on climate

Abstract: A cover article in Eos last year [Johnson, 1997] called for a dam across the Strait of Gibraltar to prevent a new Ice Age. In this article, R. G. Johnson argued that reduced Nile River flow after building the Aswan Dam increases Mediterranean Sea salinity, leading to enhanced outflow of salty water into the Atlantic Ocean. This, in turn, would alter the thermohaline (that is, temperature and salinity driven) circulation of the Atlantic, heat up the Labrador Sea and enhance evaporation there, and increase snowfall in Canada until a new ice sheet builds up. Ocean circulation model experiments, however, suggest that this fear is unfounded. While Mediterranean saltwater outflow (Figure 1a) does appear to have some effect on North Atlantic circulation and surface climate, the change in Mediterranean salt budget resulting from the Aswan Dam is far too small to have any noticeable impact.

Simulation of the global bio-geophysical interactions during the Last Glacial Maximum.

Abstract: The bio-geophysical feedbacks during the Last Glacial Maximum (LGM, 21 000 y BP) are investigated by use of an asynchronously coupled global atmosphere-biome model. It is found that the coupled model improves on the results of an atmosphere-only model especially for the Siberian region, where the inclusion of vegetation-snow-albedo interaction leads to a better agreement with geological reconstructions. Furthermore, it is shown that two stable solutions of the coupled model are possible under LGM boundary conditions. The presence of bright sand desert at the beginning of a simulation leads to more extensive subtropical deserts, whereas an initial global vegetation cover with forest, steppe, or dark desert results in a northward spread of vegetation of up to some 1000 km, mainly in the western Sahara. These differences can be explained in the framework of Charney’s theory of a “self-induction” of deserts through albedo enhancement. Moreover, it is found that the tropical easterly jet is strengthened in the case of the “green” Sahara, which in turn leads to a modification of the Indian summer monsoon.

Modern oral contraceptive use and benign liver tumors: the German Benign Liver Tumor Case-Control Study.

Abstract: Objective To analyze the association between oral contraceptive use and the risk of benign liver tumors.Methods Two parallel case-control studies on hepatocellular adenoma and focal nodular hyperpl...

Analysis of rainfall records: possible relation to self-organized criticality

Abstract: The hypothesis that rainfall might be a case of self-organized critical dynamics is tested using long-term data sets from weather stations around the world. It is found that the distribution of droughts in semi-arid regions obeys indeed a clear-cut power law. The statistics for rain intensity, on the other hand, exhibits two distinct scaling regimes. c 1998 Elsevier Science B.V. All rights reserved

Traveling waves in a reaction-diffusion system : diffusion with finite velocity and kolmogorov-petrovskii-piskunov kinetics

Abstract: An asymptotic method is presented for the analysis of the traveling waves in the one-dimensional reaction-diffusion system with the diffusion with a finite velocity and Kolmogorov-Petrovskii-Piskunov kinetics. The analysis makes use of the path-integral approach, scaling procedure, and the singular perturbation techniques involving the large deviations theory for the Poisson random walk. The exact formula for the position and speed of reaction front is derived. It is found that the reaction front dynamics is formally associated with the relativistic Hamiltonian/Lagrangian mechanics.

International cooperation behind the veil of uncertainty: the case of transboundary acidification

Abstract: The complexities of international environmental problems are only poorly understood. Hence, decision makers have to negotiate about abatement measures even though they do not know the 'true' model of the ecological system and have only a rough idea about the costs and benefits of their action. It will be analysed to what extent this kind of 'model uncertainty' – where players do not only have incomplete information about the payoff functions of the other players, but also about their own payoff function – affects the prospects of international cooperation. Using a simple game-theoretic model, it is shown how countries can use the veil of uncertainty to hide their distributional interests. The arguments are based on a deviation from the common prior assumption, which seems particularly questionable in a setting comprising various countries with different cultural and scientific backgrounds. Finally the model will prove useful to quantitatively and qualitatively illustrate the central role of model uncertainty in the negotiations of the first Sulphur Protocol signed to combat transboundary acidification.

Exposure to allopurinol and the risk of cataract extraction in elderly patients.

Abstract: Objective To determine whether exposure to allopurinol is associated with an increased risk of cataract extraction in elderly patients. Methods We conducted a case-control study using data from the Quebec universal health insurance program for all elderly patients. The 3677 cases were patients with a cataract extraction between 1992 and 1994. The 21,868 controls were randomly selected among patients not diagnosed with cataract and matched to cases on the date of the extraction. We determined the odds ratio of cataract extraction according to the cumulative dose and duration of allopurinol use relative to nonusers, using conditional logistic regression analysis. The analysis was adjusted for the effects of age, sex, diabetes mellitus, hypertension, glaucoma, and ophthalmic and oral corticosteroid exposure. Results A cumulative dose of allopurinol of more than 400 g or a duration of use of longer than 3 years were associated with an increased risk of cataract extraction, with odds ratios of 1.82 (95% confidence interval [CI], 1.18-2.80) and 1.53 (95% CI, 1.12-2.08), respectively. No increase in risk was observed for lower cumulative doses or shorter exposure periods. Conclusion Long-term administration of allopurinol increases the risk of cataract extraction in elderly patients.

Crystallization of the Supercooled Liquid Zr41Ti14Cu12.5Ni10Be22.5

Abstract: The bulk metallic glass Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 has a high glass forming ability and a wide existence range for the supercooled liquid between glass transition and crystallization. In this temperature range remarkable structural changes are observed, even after short annealing periods. We have studied the crystallization at 623 K and 673 K for different times using transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). After heat treatment of the supercooled liquid at 623 K between 5h and 508 h only a negligible fraction of small crystals (fcc, a=1.0045 nm or monoclinic, a=0.585 nm, b=0.934 nm, c=0.414 nm) is observed, while at 673 K for times between 1 h and 19 h in addition to crystallization of two new phases with fcc structure (a=0.406 nm) and with hexagonal structure (a=0.382 nm, c=0.324 nm) in agreement with the ZrBe 2 structure occurs. Preannealing at 623 K for 15 h slows down significantly the subsequent crystallization at 673 K.The TEM results are compared with results from X-ray diffractometry (XRD) and with results from small angle neutron scattering (SANS) and are discussed with respect to correlations between amorphous decomposition and crystallization.

Empirical-Quantitative Approaches to the Study of International Environmental Policy

Abstract: This article provides a concise overview of empirical-quantitative research in the field of international environmental policy. In particular, an ideal research cycle is developed which summarizes the major decisions to be taken in quantitative research. Subsequently, the contemporary quantitative research on international environmental policy and its practical challenges are assessed. The article concludes by emphasizing the various strengths of empirical-quantitative research and providing an outlook on the future of empirical-quantitative studies in the field of international environmental policy. Empirical-Quantitative Approaches 1 For understandable reasons, case selection in most studies [on international regimes] has been driven by practical considerations instead of methodological requirements. Moreover, the choice of both dependent and independent variables for systematic attention in these small-n case studies has failed, in general, to produce a cumulative and consistent set of information on an agreed upon set of important variables. Each study, in practice, has tended to select idiosyncratic variables, or operationalize common ones in radically different ways. As a result of these limitations, the study of international regimes stands out as somewhat peculiar in its absence of systematic, large-n studies making use of quantitative methods, methods which have advanced the state of the art in almost all other areas of political science. (Breitmeier, Levy, Young & Zurn, 1996b, 1) Why Empirical-Quantitative Research? Studies of international environmental policy have largely been dominated by empirical-qualitative studies, most of which employ the case study design. As Breitmeier et al. (1996b, 1) suggest for the study of international regimes, empirical-quantitative studies may assist in advancing social science research. However, very few empirical-quantitative studies in the field of international environmental policy have been undertaken so far. As Kern and Bratzel summarize Empirical-Quantitative Approaches 2 Quantitative methods are the exception in international comparative environmental policy research. ... Most studies are undertaken as case studies or comparative case studies" (Kern & Bratzel, 1996, 53, translation by the author). As the researchers using empirical-qualitative methods suggest (e.g., Bernauer & Mitchell, 1997), well-crafted case studies require particular care in order to permit valid conclusions. While case studies are likely to generate very detailed information, the degree of confidence in the findings is limited by the small number of cases (“N”) which they normally encompass. By contrast, empirical-quantitative research often shows the following characteristics: (i) medium to large number of cases (from hundreds to thousands), (ii) multiple explanatory (or exogenous) variables, and (iii) testability of elaborate structures of hypotheses.i Since experimental settings in international environmental policy hardly exist, quantitative studies will use quasi-experimental designs (Cook & Campbell, 1979).ii Empirical-quantitative methods more easily allow the use of “most different case” as opposed to “most similar case” research designs (Przeworski & Teune, 1970), but they have not been necessarily the method of choice: They require explicit theory and data both of which are not yet abundant in the field of international environmental policy. Conversely, this partially explains the attractiveness of the case study method. Fortunately, even at this point in time, there a few studies in the field of international environmental policy which apply statistical methods, and given increased efforts of data generation, empirical-quantitative research is likely to become more prominent in the foreseeable future. This trajectory may potentially resemble the trend in research on the study of civil and international war as pioneered by the datasets created in the field of international security (e.g., Small & Singer, 1982). In the following Section, I will summarize the steps to be ideally taken in empiricalquantitative research, and, subsequently, provide a brief overview of empirical-quantitative studies in the field of international environmental policy. Furthermore, the practical challenges these studies Empirical-Quantitative Approaches 3 face are reviewed. The article concludes with a summary of the advantages of quantitative research and its likely future trajectory. Designing Empirical-Quantitative Research Designing an empirical-quantitative study may easily be more demanding than subsequently executing it. The reason for this counter-intuitive conclusion lies in the risk a researcher accepts once s/he has settled for a research design and collected the data. Once data are collected, it may prove difficult to correct for problems of poor model specification, omitted variables, low data quality, missing data based on incomplete responses, or lack of multiple measurements of the same theoretical construct. Therefore, the design of an empirical-quantitative study is a crucial step warranting particular attention. Ideally, a researcher should go through the steps outlined in Table 1 in order to strive for high quality results. Table 1: The Ideal Sequence of Empirical-Quantitative Research