Showing papers by "Potsdam Institute for Climate Impact Research published in 2000"

An Anatomy of Adaptation to Climate Change and Variability

Abstract: Adaptation to climate variability and change is important both for impact assessment (to estimate adaptations which are likely to occur) and for policy development (to advise on or prescribe adaptations). This paper proposes an "anatomy of adaptation" to systematically specify and differentiate adaptations, based upon three questions: (i) adapt to what? (ii) who or what adapts? and (iii) how does adaptation occur? Climatic stimuli include changes in long-term mean conditions and variability about means, both current and future, and including extremes. Adaptation depends fundamentally on the characteristics of the system of interest, including its sensitivities and vulnerabilities. The nature of adaptation processes and forms can be distinguished by numerous attributes including timing, purposefulness, and effect. The paper notes the contribution of conceptual and numerical models and empirical studies to the understanding of adaptation, and outlines approaches to the normative evaluation of adaptation measures and strategies.

CLIMBER-2: a climate system model of intermediate complexity. Part I: model description and performance for present climate

Abstract: A 2.5-dimensional climate system model of intermediate complexity CLIMBER-2 and its perfor- mance for present climate conditions are presented. The model consists of modules describing atmosphere, ocean, sea ice, land surface processes, terrestrial vege- tation cover, and global carbon cycle. The modules in- teract through the fluxes of momentum, energy, water and carbon. The model has a coarse spatial resolution, nevertheless capturing the major features of the Earth's geography. The model describes temporal variability of the system on seasonal and longer time scales. Due to the fact that the model does not employ flux adjustments and has a fast turnaround time, it can be used to study climates significantly diAerent from the present one and to perform long-term (multimillennia) simulations. The comparison of the model results with present climate data show that the model successfully describes the seasonal variability of a large set of characteristics of the climate system, including radiative balance, tempera- ture, precipitation, ocean circulation and cryosphere.

Measuring the effectiveness of international environmental regimes

Abstract: Although past research has emphasized the importance of international regimes for international gover-nance, systematic assessments of regime effects are missing This article derives a standardized measure-ment concept for the effectiveness of international environmental regimes It is based on a simultaneous evaluation of actual policy against a no-regime counterfactual and a collective optimum Subsequently, the empirical feasibility of the measurement concept is demonstrated by way of two international treaties regu-lating transboundary air pollution in Europe The results demonstrate that the regimes indeed show positive effects;but fall substantially short of the collective optima

Incorporating dynamic vegetation cover within global climate models

Abstract: Numerical models of Earth's climate system must consider the atmosphere and terrestrial biosphere as a coupled system, with biogeophysical and biogeochemical processes occurring across a range of timescales. On short timescales (i.e., seconds to hours), the coupled system is dominated by the rapid biophysical and biogeochemical processes that exchange energy, water, carbon dioxide, and momentum between the atmosphere and the land surface. Intermediate-timescale (i.e., days to months) processes include changes in the store of soil moisture, changes in carbon allocation, and vegetation phenology (e.g., budburst, leaf-out, senescence, dormancy). On longer timescales (i.e., seasons, years, and decades), there can be fundamental changes in the vegetation structure itself (disturbance, land use, stand growth). In order to consider the full range of coupled atmosphere–biosphere processes, we must extend climate models to include intermediate and long-term ecological phenomena. This paper reviews early attempts a...

Developing adaptive forest management strategies to cope with climate change.

Abstract: Numerous investigations have indicated that projected climate change will impact strongly on forest growth and composition. To adapt managed forests to changing environmental conditions it may be necessary to modify traditional forest management strategies. An extended version of a forest gap model was applied to a managed forest district in northeastern Germany. The model was initialized with forest inventory data and run using routines devised to simulate three management scenarios: (1) maximized timber production, (2) climatically well-adapted forest composition, and (3) maximized tree species diversity. The strategies were compared with a baseline scenario of traditional management without any response to climate change. The comparisons were based on simulated wood production and species composition after 110 years of development. The results underline the important influence that management strategies have on forest growth. Forest management may adopt a variety of strategies to respond to the expected changes in climate. Process-oriented forest gap models can aid in the assessment of these strategies.

The Carbon Balance of the Terrestrial Biosphere: Ecosystem Models and Atmospheric Observations

Abstract: Precise measurements in air are helping to clarify the fate of CO2 released by human activities. Oxygen-to-nitrogen ratios in firn (the transition state from snow to ice) and archived air samples indicate that the terrestrial biosphere was approximately carbon-neutral on average during the 1980s. CO2 release by forest clearance during this period must have been compensated for by CO2 sinks elsewhere on land. Direct atmospheric O2:N2 measurements became available during the 1990s. These measurements indicate net terrestrial CO2 uptake of ∼2 Pg C/yr. From the north–south O2:N2 gradient, it has been inferred that about this amount was taken up by terrestrial ecosystems in the northern nontropics while additional CO2 released by tropical-forest clearance must have been compensated for by additional, tropical, terrestrial CO2 sinks. These and other atmospheric observations provide independent tests of carbon-cycle reconstructions made with process-based terrestrial ecosystem models. Such models can account for major features of the atmospheric-CO2 record, including the amplitude and phase of the seasonal cycle of atmospheric-CO2 concentration at different latitudes, and much of the interannual variability in the rate of increase of atmospheric CO2. Models also predict direct effects of rising atmospheric-CO2 concentration on primary production, modified by feedbacks at the plant and ecosystem levels. These effects translate into a global carbon sink the right order of magnitude to compensate for forest clearance during the 1980s. The modeled sink depends on continuously increasing CO2 to maintain disequilibrium between primary production and carbon storage. There are still substantial differences among the carbon-balance estimates made by different models, reflecting limitations in current understanding of ecosystem-level responses to atmospheric-CO2 concentration, especially with regard to the interactions of C and N cycling and interactions with land-use change. Scenario calculations nevertheless agree that if atmospheric CO2 continues its rise unchecked then the terrestrial sink will start to decline by the middle of the next century, for reasons including saturation of the direct CO2 effect on photosynthesis.

Explaining forest composition and biomass across multiple biogeographical regions

Abstract: Current scientific concerns regarding the impacts of global change include the responses of forest composition and biomass to rapid changes in climate, and forest gap models have often been used to address this issue. These models reflect the concept that forest composition and biomass in the absence of large-scale disturbance are explained by competition among species for light and other resources in canopy gaps formed when dominant trees die. Since their intiation 25 yr ago, a wide variety of gap models have been developed that are applicable to different forest ecosystems all over the world. Few gap models, however, have proved to be equally valid over a wide range of environmental conditions, a problem on which our work is focused. We previously developed a gap model that is capable of simulating forest composition and biomass in temperate forests of Europe and eastern North America based on a single model structure. In the present study, we extend the model to simulate individual tree species response to strong moisture seasonality and low temperature seasonality, and we modify the widespread parabolic temperature response function to mimic nonlinear increases in growth with increased temperature up to species-specific optimal values. The resulting gap model, ForClim V2.9, generates realistic projections of tree species composition and biomass across a complex gradient of temperature and moisture in the Pacific Northwest of the United States. The model is evaluated against measured basal area and stand structure data at three elevations of the H. J. Andrews LTER site, yielding satisfactory results. The very same model also provides improved estimates of species composition and stand biomass in eastern North America and central Europe, where it originated. This suggests that the model modifications we introduced are indeed generic. Temperate forests other than those we studied here are characterized by climates that are quite similar to the ones in the three study regions. Therefore we are confident that it is possible to explain forest composition and biomass of all major temperate forests by means of a single hypothesis as embodied in a forest gap model.

Mid-Holocene greening of the Sahara: first results of the GAIM 6000 year BP Experiment with two asynchronously coupled atmosphere/biome models

Abstract: The mid-Holocene `green' Sahara represents the largest anomaly of the atmosphere-biosphere system during the last 12 000 years. Although this anomaly is attributed to precessional forcing leading to a strong enhancement of the African monsoon, no climate model so far has been able to simulate the full extent of vegetation in the Sahara region 6000 years ago. Here two atmospheric general circulation models (LMD 5.3 and ECHAM 3) are asynchronously coupled to an equilibrium biogeography model to give steady-state simulations of climate and vegetation 6000 years ago, including biogeophysical feedback. The two model results are surprisingly different, and neither is fully realistic. ECHAM shows a large northward extension of vegetation in the western part of the Sahara only. LMD shows a much smaller and more zonal vegetation shift. These results are unaffected by the choice of `green' or modern initial conditions. The inability of LMD to sustain a `green' Sahara 6000 years ago is linked to the simulated strength of the tropical summer circulation. During the northern summer monsoon season, the meridional gradient of sea-level pressure and subsidence over the western part of northern Africa are both much weaker in ECHAM than in LMD in the present as well as the mid-Holocene. These features allow the surface moist air flux to penetrate further into northern Africa in ECHAM than in LMD. This comparison illustrates the importance of correct simulation of atmospheric circulation features for the sensitivity of climate models to changes in radiative forcing, particularly for regional climates where atmospheric changes are amplified by biosphere-atmosphere feedbacks.

Recent climate change in the North Atlantic/European sector

Abstract: The climate variability of the North Atlantic:European sector is characterized by large-scale circulation patterns measured in terms of a time series of two binary variables: the occurrence of a Grosswetter state and of a cluster set of meridional sea level pressure (SLP) gradients (characterizing the westerlies). An outlier test of the decadal behaviour of the residence time of these states identifies the decade 1981‐1990 to be the first outlier. The climatological embedding and a possible stochastic:dynamical interpretation are presented. Copyright © 2000 Royal Meteorological Society.

Modelling the vegetation of China using the process-based equilibrium terrestrial biosphere model BIOME3

Abstract: 1 We model the potential vegetation and annual net primary production (NPP) of China on a 10' grid under the present climate using the processed-based equilibrium terrestrial biosphere model BIOME3. The simulated distribution of the vegetation was in general in good agreement with the potential natural vegetation based on a numerical comparison between the two maps using the DeltaV statistic (DeltaV = 0.23). Predicted and measured NPP were also similar, especially in terms of biome-averages. 2 A coupled ocean-atmosphere general circulation model including sulphate aerosols was used to drive a double greenhouse gas scenario for 2070-2099. Simulated vegetation maps from two different CO2 scenarios (340 and 500 p.p.m.v.) were compared to the baseline biome map using DeltaV. Climate change alone produced a large reduction in desert, alpine tundra and ice/polar desert, and a general pole-ward shift of the boreal, temperate deciduous, warm-temperate evergreen and tropical forest belts, a decline in boreal deciduous forest and the appearance of tropical deciduous forest. The inclusion of CO2 physiological effects led to a marked decrease in moist savannas and desert, a general decrease for grasslands and steppe, and disappearance of xeric woodland/scrub. Temperate deciduous broadleaved forest, however, shifted north to occupy nearly half the area of previously temperate mixed forest. 3 The impact of climate change and increasing CO2 is not only on biogeography, but also on potential NPP. The NPP values for most of the biomes in the scenarios with CO2 set at 340 p.p.m.v. and 500 p.p.m.v. are greater than those under the current climate, except for the temperate deciduous forest, temperate evergreen broadleaved forest, tropical rain forest, tropical seasonal forest, and xeric woodland/scrub biomes. Total vegetation and total carbon is simulated to increase significantly in the future climate scenario, both with and without the CO2 direct physiological effect. 4 Our results show that the global process-based equilibrium terrestrial biosphere model BIOME3 can be used successfully at a regional scale. (Less)

Citizens’ perspectives on climate change and energy use

Abstract: In the beginnings of climate change policy, results from the natural sciences were essential for motivating the establishment of global change diplomacy. At present it is increasingly being recognised that these results must be combined with findings from the social sciences if effective climate policy is to emerge. In particular, participatory techniques for the involvement of stakeholders, ranging from ordinary citizens to business people, are needed. The paper presents the methodology of Integrated Assessment (IA)-Focus Groups, designed primarily for involving citizens in Integrated Assessments of complex issues like climate change. It focuses on collages produced by European IA-Focus Group participants faced with alternative possibilities of energy use. The results suggest that citizens across Europe see strong reductions of current levels of energy use as more desirable than a business-as-usual perspective. Moreover, they indicate that the opinion formation by citizens is by no means restricted to unambiguous stereotypes. We relate these findings to the concept of `reflexive modernisation', stressing the importance of uncertainty and ambiguity in environmental debates. Implications for representing uncertainty in IA models are discussed.

Asymptotic Analyses for Atmospheric Flows and the Construction of Asymptotically Adaptive Numerical Methods

Abstract: Prandtl’s boundary layer theory may be considered one of the origins of systematic scale analysis and asymptotics in fluid mechanics. Due to the vast scale differences in atmospheric flows such analyses have a particularly strong tradition in theoretical meteorology. Simplified asymptotic limit equations,derive d through scale analysis,yield a deep insight into the dynamics of the atmosphere. Due to limited capacities of even the fastest computers, the use of such simplified equations has traditionally been a necessary precondition for successful approaches to numerical weather forecasting and climate modelling. In the face of the continuing increase of available compute power there is now a strong tendency to relax as many simplifying scaling assumptions as possible and to go back to more complete and more complex balance equations in atmosphere flow computations. However,the simplified equations obtained through scaling analyses are generally associated with singular asymptotic limits of the full governing equations,and this has important consequences for the numerical integration of the latter. In these singular limit regimes dominant balances of a few terms in the governing equations lead to degeneracies and singular changes of the mathematical structure of the equations. Numerical models based on comprehensive equation systems must simultaneously represent these dominant balances and the subtle,but important,deviations from them. These requirements are partly in contradiction,and this can lead to severe restrictions of the accuracy and/or efficiency of numerical models. The present paper makes a case for a somewhat unconventional use of the results of scale analyses and multiple scales asymptotics. It demonstrates how,thr ough the judicious implementation of asymptotic results,numeric al discretizations of the full governing equations can be designed so that they operate with uniform accuracy and efficiency even when a singular limit regime is approached.

Comparison of the last interglacial climate simulated by a coupled global model of intermediate complexity and an AOGCM

Abstract: The climate at the Last Interglacial Maximum (125 000 years before present) is investigated with the atmosphere-ocean general circulation model ECHAM-1/LSG and with the climate system model of intermediate complexity CLIMBER-2. Comparison of the results of the two models reveals broad agreement in most large-scale features, but also some discrepancies. The fast turnaround time of CLIMBER-2 permits one to perform a number of sensitivity experiments to (1) investigate the possible reasons for these differences, in particular the impact of different freshwater fluxes to the ocean, (2) analyze the sensitivity of the results to changes in the definition of the modern reference run concerning CO2 levels (preindustrial versus “present”), and (3) estimate the role of vegetation in the changed climate. Interactive vegetation turns out to be capable of modifying the initial climate signals significantly, leading especially to warmer winters in large parts of the Northern Hemisphere, as indicated by various paleodata. Differences due to changes in the atmospheric CO2 content and due to interactive vegetation are shown to be at least of the same order of magnitude as differences between the two completely different models, demonstrating the importance of careful experimental design.

Reduction of biosphere life span as a consequence of geodynamics

Abstract: The long-term co-evolution of the geosphere–biospere complex from the Proterozoic up to 15 billion years into the planet's future is investigated using a conceptual earth system model including the basic geodynamic processes The model focusses on the global carbon cycle as mediated by life and driven by increasing solar luminosity and plate tectonics The main CO 2 sink, the weathering of silicates, is calculated as a function of biologic activity, global run-off and continental growth The main CO 2 source, tectonic processes dominated by sea-floor spreading, is determined using a novel semi-empirical scheme Thus, a geodynamic extension of previous geostatic approaches can be achieved As a major result of extensive numerical investigations, the “terrestrial life corridor”, ie, the biogeophysical domain supporting a photosynthesis-based ecosphere in the planetary past and in the future, can be identified Our findings imply, in particular, that the remaining life-span of the biosphere is considerably shorter (by a few hundred million years) than the value computed with geostatic models by other groups The “habitable-zone concept” is also revisited, revealing the band of orbital distances from the sun warranting earth-like conditions It turns out that this habitable zone collapses completely in some 14 billion years from now as a consequence of geodynamics DOI: 101034/j1600-0889200000898x

Scaling Issues in Forest Succession Modelling

Abstract: This paper reviews scaling issues in forest succession modelling, focusing on forest gap models. Two modes of scaling are distinguished: (1) implicit scaling, i.e. taking scale-dependent features into account while developing model equations, and (2) explicit scaling, i.e. using procedures that typically involve numerical simulation to scale up the response of a local model in space and/or time. Special attention is paid to spatial upscaling methods, and downscaling is covered with respect to deriving scenarios of climatic change to drive gap models in impact assessments. When examining the equations used to represent ecological processes in forest gap models, it becomes evident that implicit scaling is relevant, but has not always been fully taken into consideration. A categorization from the literature is used to distinguish four methods for explicit upscaling of ecological models in space: (1) Lumping, (2) Direct extrapolation, (3) Extrapolation by expected value, and (4) Explicit integration. Examples from gap model studies are used to elaborate the potential and limitations of these methods, showing that upscaling to areas as large as 3000 km2 is possible, given that there are no significant disturbances such as fires or insect outbreaks at the landscape scale. Regarding temporal upscaling, we find that it is important to consider migrational lags, i.e. limited availability of propagules, if one wants to assess the transient behaviour of forests in a changing climate, specifically with respect to carbon storage and the associated feedbacks to the atmospheric CO2 content. Regarding downscaling, the ecological effects of different climate scenarios for the year 2100 were compared at a range of sites in central Europe. The derivation of the scenarios is based on (1) imposing GCM grid-cell average changes of temperature and precipitation on the local weather records; (2) a qualitative downscaling technique applied by the IPCC for central and southern Europe; and (3) statistical downscaling relating large-scale circulation patterns to local weather records. Widely different forest compositions may be obtained depending on the local climate scenario, suggesting that the downscaling issue is quite important for assessments of the ecological impacts of climatic change on forests.

Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 2. Net assimilation and stomatal conductance of leaves

Abstract: Atmospheric CO2 concentration continues to rise. It is important, therefore, to determine what acclimatory changes will occur within the photosynthetic apparatus of wheat (Triticum aestivum L. cv. Yecora Rojo) grown in a future high-CO2 world at ample and limited soil N contents. Wheat was grown in an open field exposed to the CO2 concentration of ambient air [370 μmol (CO2) mol−1; Control] and air enriched to ∼200 μmol (CO2) mol−1 above ambient using a Free-Air CO2 Enrichment (FACE) apparatus (main plot). A High (35 g m−2) or Low (7 and 1.5 g m−2 for 1996 and 1997, respectfully) level of N was applied to each half of the main CO2 treatment plots (split-plot). Under High-N, FACE reduced stomatal conductance (gs) by 30% at mid-morning (2 h prior to solar noon), 36% at midday (solar noon) and 27% at mid-afternoon (2.5 h after solar noon), whereas under Low-N, gs was reduced by as much as 31% at mid-morning, 44% at midday and 28% at mid-afternoon compared with Control. But, no significant CO2 × N interaction effects occurred. Across seasons and growth stages, daily accumulation of carbon (A′) was 27% greater in FACE than Control. High-N increased A′ by 18% compared with Low-N. In contrast to results for gs, however, significant CO2 × N interaction effects occurred because FACE increased A′ by 30% at High-N, but by only 23% at Low-N. FACE enhanced the seasonal accumulation of carbon (A′′) by 29% during 1996 (moderate N-stress), but by only 21% during 1997 (severe N-stress). These results support the premise that in a future high-CO2 world an acclimatory (down-regulation) response in the photosynthetic apparatus of field-grown wheat is anticipated. They also demonstrate, however, that the stimulatory effect of a rise in atmospheric CO2 on carbon gain in wheat can be maintained if nutrients such as nitrogen are in ample supply.

Response of a river catchment to climatic change: Application of expanded downscaling to northern Germany

Abstract: We used the technique of expanded General Circulation Model (GCM) downscalingto derive time series of daily weather for the analysis of potential climaticchange impact on a river catchment in Northern Germany. The derived timeseries was then fed into a spatially distributed hydrological model tosimulate various water balance components and river discharge. All componentsof this modelling approach are known to provide fairly accurate results undernormal (current) climatic conditions. Hydrological time series, theirstatistics and spatial patterns of various water balance components, resultingfrom a `business-as-usual' emission scenario, were analysed. The simulationresults showed that if everything apart from climate is held constant, asignificant increase in river discharge may be expected in the coming decadesas a consequence of increased rainfall amounts. Although the modellingapproach provides an operational way of performing watershed climate changeimpact studies, many uncertainties still have to be considered.

Geographic patterns and dynamics of Alaskan climate interpolated from a sparse station record

Abstract: Summary Data from a sparse network of climate stations in Alaska were interpolated to provide 1-km resolution maps of mean monthly temperature and precipitation–-variables that are required at high spatial resolution for input into regional models of ecological processes and resource management. The interpolation model is based on thin-plate smoothing splines, which uses the spatial data along with a digital elevation model to incorporate local topography. The model provides maps that are consistent with regional climatology and with patterns recognized by experienced weather forecasters. The broad patterns of Alaskan climate are well represented and include latitudinal and altitudinal trends in temperature and precipitation and gradients in continentality. Variations within these broad patterns reflect both the weakening and reduction in frequency of low-pressure centres in their eastward movement across southern Alaska during the summer, and the shift of the storm tracks into central and northern Alaska in late summer. Not surprisingly, apparent artifacts of the interpolated climate occur primarily in regions with few or no stations. The interpolation model did not accurately represent low-level winter temperature inversions that occur within large valleys and basins. Along with well-recognized climate patterns, the model captures local topographic effects that would not be depicted using standard interpolation techniques. This suggests that similar procedures could be used to generate high- resolution maps for other high-latitude regions with a sparse density of data.

Alternative forest management strategies under climatic change - prospects for gap model applications in risk analyses.

Abstract: The projected global climate change will influence growth and productivity of natural and managed forests. Since the characteristics of the future regional climate are still uncertain and the response of our forests to changes in the atmospheric and climatic conditions may be both positive or negative, decision making in managed forests should consider the new risks and uncertainties arising from climatic change, especially if the rotation periods are long. An extended version of the forest gap model FORSKA was applied to simulate the forest development at 488 forest inventory plots in the federal state of Brandenburg, Germany, under two climate and three management scenarios. The transient growth dynamics from 1990 to 2100 were investigated at four sites in different parts of the state, representing the variability of environmental and forest conditions within Brandenburg. The alternative management strategies led to distinct differences in forest composition after 110 years of simulation. The projected climate change affected both forest productivity and species composition. The impacts of alternative management scenarios are discussed. It is concluded that the extended forest gap model can be a valuable tool to support decision making in forest management under global change.

Application of volume growth and survival graphs in the evaluation of four process-based forest growth models.

Abstract: Volume growth and survival (VGS) graphs, which show volume growth rate and risk of mortality for individual trees (or tree size classes), have been proposed as a tool for assessing the validity of models that describe the development over time of tree size distributions within forest stands. We examined the utility of the VGS method in evaluating four process-based models. The performance of the models FORSKA, 4C, MORG, and PipeQual is analyzed against long-term data from a Scots pine stand in Evo, Finland, and the models FORSKA and 4C are also assessed with respect to data from a beech stand in Fabrikschleichach, Germany. Comparison of the measurement-based VGS graphs with those produced from the model-based data shows that although the models yield similar stand-level predictions, they can differ widely in their projections of individual tree growth and size distributions. Examination of the discrepancies between models and data in the context of the VGS graphs reveals several areas in which the models could be improved. We conclude that the method is useful in model evaluation, especially if used in combination with indicators of stand structure, such as the height/diameter ratio.

Integrated modelling of water availability and water use in the semi-arid Northeast of Brazil

Abstract: Scarcity of water resources is a. major constraint for development in the semi-arid Northeast of Brazil. Quantification of natural water availability and of water use are key issues within a comprehensive Brazilian-German research project. This paper gives an overview of the integrated hydrological and water use modelling for the federal Brazilian states of Ceara and Piaui covering an area of over 470 000 km2. The model subdivides the area into administrative sub-units (municipalities) of in average about 1000 km2. and uses daily time-steps. The hydrological module is designed to account for: water availability (in terms of river runoff, reservoir storage, groundwater recharge and soil moisture), influence of climate and land-use changes on water balance, large spatial scale (acknowledging the uncertainty of model results in view of scarce data), and specific semi-arid hydroclimatological conditions. This version of the water use module includes domestic, animal and irrigation water uses. The withdrawal water use and consumptive water use can approximately be calculated for the present situation of the municipalities. First results of the two modules and the effects of their interlinkages are presented