Climate modeling

Critique of the tracer-tracer correlation technique and its potential to analyze polar ozone loss in chemistry-climate models

by Carsten Lemmen

Co-authored with Rolf Müller, Paul Konopka, and Martin Dameris

The tracer-tracer correlation technique (TRAC) has been widely employed to infer chemical ozone loss from... more The tracer-tracer correlation technique (TRAC) has been widely employed to infer chemical ozone loss from observations. Yet, its applicability to chemistry-climate model(CCM) data is disputed. Here, we report the successful application of TRAC on theresults of a CCM simulation. By comparing TRAC-calculated ozone loss to ozone lossderived with the passive ozone method in a chemistry transport model we differentiateeffects of internal mixing and cross vortex boundary mixing on a TRAC referencecorrelation. As a test case, we consider results of a cold Arctic winter/spring episode froman E39/C experiment, where typical features, for example, sufficient polar stratosphericcloud formation potential, denitrification and dehydration, and intermittent and finalstratospheric warming events, are simulated. We find that internal mixing does not impact the TRAC-derived reference correlation at all. Mixing across the vortex boundary wouldlead to an underestimation of ozone loss by 10% when calculated with TRAC. We provide arguments that TRAC is a consistent and conservative method to derive chemicalozone loss and can be used to extract its chemical signature also from CCM simulations. As a consequence, we will be able to provide a lower bound for chemical ozone loss for model simulations where a passive ozone tracer is not available

The socioeconomics of food crop production and climate change vulnerability: a global scale quantitative analysis of how grain crops are sensitive to drought

by Simon Gosling

Many studies warn that climate change may undermine global food security. Much work on this topic focuses on modelling... more Many studies warn that climate change may undermine global food security. Much work on this topic focuses on modelling crop-weather interactions but these models do not generally account for the ways in which socio-economic factors influence how harvests are affected by weather. To address this gap, this paper uses a quantitative harvest vulnerability index based on annual soil moisture and grain production data as the dependent variable in a Linear Mixed Effects model with national scale socio-economic data as independent variables for the period 1990–2005. Results show that rice, wheat and maize production in middle income countries were especially vulnerable to droughts. By contrast, harvests in countries with higher investments in agriculture (e.g. higher amounts of fertilizer use) were less vulnerable to drought. In terms of differences between the world’s major grain crops, factors that made rice and wheat crops vulnerable to drought were quite consistent, while those of maize crops varied considerably depending on the type of region. This is likely due to the fact that maize is produced under very different conditions worldwide. One recommendation for reducing drought vulnerability risks is coordinated development and adaptation policies, including institutional support that enables farmers to take proactive action.

Sensitivity of a general circulation model to global changes in leaf area index

by Timothy Kittel

Chase, T.N., R.A. Pielke, T.G.F. Kittel, R. Nemani, and S.W. Running. 1996. Sensitivity of a general circulation model to global changes in leaf area index. Journal of Geophysical Research 101:7393-7408. doi:10.1029/95JD02417

Methods have recently become available for estimating the amount of leaf area at the surface of the Earth using... more Methods have recently become available for estimating the amount of leaf area at the surface of the Earth using satellite data. Also available are modeled estimates of what global leaf area patterns would look like should the vegetation be in equilibrium with current local climatic and soil conditions. The differences between the actual vegetation distribution and the potential vegetation distribution may reflect the impact of human activity on the Earth's surface. To examine model sensitivity to changes in leaf area index (LAI), global distributions of maximum LAI were used as surface boundary conditions in the National Center for Atmospheric Research community climate model (NCAR CCM2) coupled with the biosphere atmosphere transfer scheme (BATS). Results from 10-year ensemble averages for the months of January and July indicate that the largest effects of the decreased LAI in the actual LAI simulation occur in the northern hemisphere winter at high latitudes despite the fact that direct LAI forcing is negligible in these regions at this time of year. This is possibly a result of LAI forcing in the tropics which has long-ranging effects in the winter of both hemispheres. An assessment of the Asian monsoon region for the month of July shows decreased latent heat flux from the surface, increased surface temperature, and decreased precipitation with the actual LAI distribution. While the statistical significance of the results has not been unambiguously established in these simulations, we suspect that an effect on modeled general circulation dynamics has occurred due to changes of maximum LAI suggesting that further attention needs to be paid to the accurate designation of vegetation parameters. The incorporation of concomitant changes in albedo, vegetation fractional coverage, and roughness length is suggested for further research.

Intercomparsion of regional biases and doubled CO2-sensitivity of coupled atmosphere-ocean general circulation model experiments

by Timothy Kittel

Full citation--
Kittel, T.G.F., F. Giorgi, and G.A. Meehl. 1998. Intercomparison of regional biases and doubled CO2-sensitivity of coupled atmosphere-ocean general circulation model experiments. Climate Dynamics 14:1-15. DOI: 10.1007/s003820050204

We compared regional biases and transient doubled CO2 sensitivities of nine coupled atmosphere-ocean general... more We compared regional biases and transient doubled CO2 sensitivities of nine coupled atmosphere-ocean general circulation models (GCMs) from six international climate modeling groups. We evaluated biases and responses in winter and summer surface air temperatures and precipitation for seven subcontinental regions, including those in the 1990 Intergovernmental Panel on Climate Change (IPCC) Scientific Assessment. Regional biases were large and exceeded the variance among four climatological datasets, indicating that model biases were not primarily due to uncertainty in observations. Model responses to altered greenhouse forcing were substantial (average temperature change=2.7±0.9 °C, range of precipitation change =-35 to +120% of control). While coupled models include more climate system feedbacks than earlier GCMs implemented with mixed-layer ocean models, inclusion of a dynamic ocean alone did not improve simulation of long-term mean climatology nor increase convergence among model responses to altered greenhouse gas forcing. On the other hand, features of some of the coupled models including flux adjustment (which may have simply masked simulation errors), high horizontal resolution, and estimation of screen height temperature contributed to improved simulation of long-term surface climate. The large range of model responses was partly accounted for by inconsistencies in forcing scenarios and transient-simulation averaging periods. Nonetheless, the models generally had greater agreement in their sensitivities than their controls did with observations. This suggests that consistent, large-scale response features from an ensemble of model sensitivity experiments may not depend on details of their representation of present-day climate.

Coupled atmosphere–biophysics–hydrology models for environmental modeling

by Timothy Kittel

Walko, R.L., L.E. Band, J. Baron, T.G.F. Kittel, R. Lammers, T.J. Lee, R.A. Pielke, Sr., C. Taylor, C. Tague, C.J. Tremback, and P.L. Vidale. 2000. Coupled atmosphere-biophysics-hydrology models for environmental modeling. Journal of Applied Meteorology 39:931-944. doi: 10.1175/1520-0450(2000)039<0931:CABHMF>2.0.CO;2

The formulation and implementation of LEAF-2, the Land Ecosystem–Atmosphere Feedback model, which comprises the... more The formulation and implementation of LEAF-2, the Land Ecosystem–Atmosphere Feedback model, which comprises the representation of land–surface processes in the Regional Atmospheric Modeling System (RAMS), is described. LEAF-2 is a prognostic model for the temperature and water content of soil, snow cover, vegetation, and canopy air, and includes turbulent and radiative exchanges between these components and with the atmosphere. Subdivision of a RAMS surface grid cell into multiple areas of distinct land-use types is allowed, with each subgrid area, or patch, containing its own LEAF-2 model, and each patch interacts with the overlying atmospheric column with a weight proportional to its fractional area in the grid cell. A description is also given of TOPMODEL, a land hydrology model that represents surface and subsurface downslope lateral transport of groundwater. Details of the incorporation of a modified form of TOPMODEL into LEAF-2 are presented. Sensitivity tests of the coupled system are presented that demonstrate the potential importance of the patch representation and of lateral water transport in idealized model simulations. Independent studies that have applied LEAF-2 and verified its performance against observational data are cited. Linkage of RAMS and TOPMODEL through LEAF-2 creates a modeling system that can be used to explore the coupled atmosphere–biophysical–hydrologic response to altered climate forcing at local watershed and regional basin scales.

Climate-mediated changes to mixed-layer properties in the Southern Ocean: assessing the phytoplankton response

by Robert Strzepek

P. W. Boyd, S. C. Doney, R. Strzepek, J. Dusenberry, K. Lindsay, and I. Fung

Concurrent changes in ocean chemical and phys- tests/metrics that will reflect the relative plasticity of different... more Concurrent changes in ocean chemical and phys- tests/metrics that will reflect the relative plasticity of different ical properties influence phytoplankton dynamics via alter- phytoplankton functional groups and/or species to respond to ations in carbonate chemistry, nutrient and trace metal inven- changing ocean conditions.
tories and upper ocean light environment. Using a fully cou-
pled, global carbon-climate model (Climate System Model 1.4-carbon), we quantify anthropogenic climate change rela- tive to the background natural interannual variability for the Southern Ocean over the period 2000 and 2100. Model re- sults are interpreted using our understanding of the environ- mental control of phytoplankton growth rates – leading to two major findings. Firstly, comparison with results from phytoplankton perturbation experiments, in which environ- mental properties have been altered for key species (e.g., bloom formers), indicates that the predicted rates of change in oceanic properties over the next few decades are too sub- tle to be represented experimentally at present. Secondly, the rate of secular climate change will not exceed background natural variability, on seasonal to interannual time-scales, for at least several decades – which may not provide the pre- vailing conditions of change, i.e. constancy, needed for phy- toplankton adaptation. Taken together, the relatively subtle environmental changes, due to climate change, may result in adaptation by resident phytoplankton, but not for several decades due to the confounding effects of climate variabil- ity. This presents major challenges for the detection and at- tribution of climate change effects on Southern Ocean phy- toplankton. We advocate the development of multi-faceted

Mullan, D.J., Favis-Mortlock, D.T. and Fealy, R. (2012) Addressking key limitations associated with modelling soil erosion under the impacts of future climate change. Agricultural and Forest Meteorology 156: 18-30.

by Donal Mullan

The benefits of quantifying climate model uncertainty in climate change impacts assessment: an example with heat-related mortality change estimates

by Simon Gosling

Values and uncertainties in the predictions of global climate models

by Eric Winsberg

Over the last several years, there has been an explosion of interest and attention devoted to the problem of... more Over the last several years, there has been an explosion of interest and attention devoted to the problem of Uncertainty Quantification (UQ) in climate science – that is, to giving quantitative estimates of the degree of uncertainty associated with the predictions of global and regional climate models. The technical challenges associated with this project are formidable, and so the statistical community has understandably devoted itself primarily to overcoming them. But as these technical challenges are being met, a number of persistent
conceptual difficulties remain. So why is UQ so important in climate science? UQ, I would like to argue, is first and foremost a tool for communicating knowledge from experts to policymakers in a way that is meant to be free from the influence of social and ethical values. But the standard ways of using probabilities to separate ethical and social values from scientific practice cannot be applied in much of climate modeling, because the roles of values in creating the models cannot be discerned after the fact—the models are too complex and the result of too much distributed epistemic labor. I argue, therefore, that typical approaches for handling ethical/social values in science do not work
well here.

Low-noise projections of complex simulator output: A useful tool when checking for code errors

by Tamsin Edwards

Rougier, JC, Edwards, TL, Collins, M & Sexton, DMH. 'Low-noise projections of complex simulator output: A useful tool when checking for code errors', Workshop on Representing Model Uncertainty and Error in Numerical Weather and Climate Prediction Models, (pp. 209-220), 2011.

A natural strategy to check for errors in a complex code, such as a computer simulator of weather or climate, is to... more A natural strategy to check for errors in a complex code, such as a computer simulator of weather or climate, is to make physically meaningful perturbations in the simulator parameters, and compare the results of the simulator runs against intuition. Such a strategy must balance the competing demands for CPU cycles of (i) performing many perturbations, and (ii) using long time-averages to suppress the effect of simulator noise. This paper proposes a mathematical solution which can be use to sharpen the perturbation signal in a given ensemble, namely to project the simulator output onto the column-space of linear combinations that maximise the signal-to-noise ratio. There are more refined approaches, but ours is easy to understand and to compute.

Environmental control of open-ocean phytoplankton groups: Now and in the future

by Robert Strzepek

Boyd, Philip W., Robert Strzepek, Feixue Fu, and David A. Hutchins

Climate change will alter concurrently many environmental factors that exert control over oceanic phytoplankton.... more Climate change will alter concurrently many environmental factors that exert control over oceanic phytoplankton. Recent laboratory culture work, shipboard experiments, and field surveys reveal many remaining unknowns about the bottom-up controls for five globally important algal groups. Increasing uncertainties exist, respectively, for picocyanobacteria, diatoms, Phaeocystis spp., N(2)-fixing cyanobacteria, and coccolithophores. This missing information about current environmental controls will hinder progress in modeling how these phytoplankton will be influenced by climate change. A review of conceptual approaches used to elucidate the relationship between environmental controls and phytoplankton dominance, from Margalef's mandala to functional traits, uncovered limitations regarding their application to climate-change scenarios. For example, these previous approaches have insufficient scope or dimensions to take into account the confounding effects of synergistic and antagonistic interactions of multiple environmental change variables. A new approach is needed that considers all of the different environmental properties altered by climate change and their interactions while at the same time permitting a subset of the most significant controls for a specific phytoplankton group to be isolated and evaluated in factorial matrix perturbation experiments. We advocate three new interlinked approaches, including environmental clusters that incorporate all factors (temperature, CO(2), light, nutrients, and trace metals), which both exert control over present-day floristics and will be altered by climate change. By carefully linking a holistic conceptual approach to a reductionist experimental design, the future responses of open-ocean phytoplankton groups to a complex, rapidly changing environment can be better predicted.

The Late Miocene climate response to a modern Sahara desert

by Jussi Eronen

The climate cooling and vegetation changes in the Miocene/Pliocene are generally well documented by various proxy... more The climate cooling and vegetation changes in the Miocene/Pliocene are generally well documented by various proxy data. Some important ecosystem changes occurred at that time. Palaeobotanical evidence suggests that the Sahara desert first appeared in the Pliocene, whereas in the Miocene North Africa was green. In the present study, we investigate the Late Miocene climate response to the appearance of the Sahara desert from a climate modelling sensitivity experiment. We compare a model experiment, which includes a full set of Late Miocene boundary conditions, with another one using the same boundary conditions except that the North African vegetation refers to the present-day situation. Our sensitivity study demonstrates that the introduction of the Sahara desert leads to a cooling and an aridification in Africa. In addition, we observe teleconnection patterns related to the North African desertification at around the Miocene/Pliocene boundary. From our sensitivity experiment, we observe that the Sahara contributes to a cooling in Central Asia and in North America. As compared to hypsodonty data for Central Asia, an increased aridity is underestimated in the Sahara experiment. Finally, we observe that the introduction of the Sahara leads to a cooling in the northern high latitudes. Hence, our sensitivity experiment indicates that the appearance of the Sahara desert is one piece to better understand Late Cenozoic climate cooling being most pronounced in the high latitudes.

A regional climate model experiment to investigate the Asian monsoon in the Late Miocene.

by Jussi Eronen

The Late Miocene (11.6–5.3 Ma) is a crucial period in the history of the Asian monsoon. Significant changes in the... more The Late Miocene (11.6–5.3 Ma) is a crucial period in the history of the Asian monsoon. Significant changes in the Asian climate regime have been documented for this period, which saw the formation of the modern Asian monsoon system. However, the spatiotemporal structure of these changes is still ambiguous, and the associated mechanisms are debated. Here, we present a simulation of the average state of the Asian monsoon climate for the Tortonian (11–7 Ma) using the regional climate model CCLM3.2. We employ relatively high spatial resolution (1° × 1°) and adapt the physical boundary conditions such as topography, land-sea distribution and vegetation in the regional model to represent the Late Miocene. As climatological forcing, the output of a Tortonian run with a fully-coupled atmosphere-ocean general circulation model is used. Our regional Tortonian run shows a stronger-than-present East Asian winter monsoon wind as a result of the enhanced mid-latitude westerly wind of our global forcing and the lowered present-day northern Tibetan Plateau in the regional model. The summer monsoon circulation is generally weakened in our regional Tortonian run compared to today. However, the changes of summer monsoon precipitation exhibit major regional differences. Precipitation decreases in northern China and northern India, but increases in southern China, the western coast and the southern tip of India. This can be attributed to the changes in both the regional topography (e.g. the lower northern Tibetan Plateau) and the global climate conditions (e.g. the higher sea surface temperature). The spread of dry summer conditions over northern China and northern Pakistan in our Tortonian run further implies that the monsoonal climate may not have been fully established in these regions in the Tortonian. Compared with the global model, the high resolution regional model highlights the spatial differences of the Asian monsoon climate in the Tortonian, and better characterizes the convective activity and its response to regional topographical changes. It therefore provides a useful and compared to global models, a complementary tool to improve our understanding of the Asian monsoon evolution in the Late Miocene.

Distribution history and climatic controls of the Late Miocene Pikermian chronofauna

by Jussi Eronen

The Late Miocene development of faunas and environments in western Eurasia is well known, but the climatic and... more The Late Miocene development of faunas and environments in western Eurasia is well known, but the climatic and environmental processes that controlled its details are incompletely understood. Here we map the rise and fall of the classic Pikermian fossil mammal chronofauna between 12 and 4.2 Ma, using genus-level faunal similarity between localities. To directly relate land mammal community evolution to environmental change, we use the hypsodonty paleoprecipitation proxy and paleoclimate modeling. The geographic distribution of faunal similarity and paleoprecipitation in successive timeslices shows the development of the open biome that favored the evolution and spread of the open-habitat adapted large mammal lineages. In the climate model run, this corresponds to a decrease in precipitation over its core area south of the Paratethys Sea. The process began in the latest Middle Miocene and climaxed in the medial Late Miocene, about 7– 8 million years ago. The geographic range of the Pikermian chronofauna contracted in the latest Miocene, a time of increasing summer drought and regional differentiation of habitats in Eastern Europe and Southwestern Asia. Its demise at the Miocene-Pliocene boundary coincides with an environmental reversal toward increased humidity and forestation, changes inevitably detrimental to open-adapted, wide-ranging large mammals.

Analysis of heat transport mechanisms from a Late Miocene model experiment with a fully-coupled atmosphere-ocean general circulation model

by Jussi Eronen

The fossil record for the Late Miocene indicates that high latitudes were warmer than today and that the... more The fossil record for the Late Miocene indicates that high latitudes were warmer than today and that the equator-to-pole temperature gradient was weak. Experiments with climate models have not been sufficiently able to represent warm polar conditions for the Late Miocene. This demonstrates that our explanation of warm high latitudes in the Late Miocene is not complete. In addition, heat transport mechanisms have not been so frequently addressed to understand the differences between the Late Miocene and modern climate. Here we present a model simulation for the Tortonian (11 to 7 Ma) using a complex fully-coupled atmosphere–ocean general circulation model to address heat transport mechanisms relative to modern conditions. Because of an open Central American Isthmus, the zonal mean northward ocean heat transport in the Northern Hemisphere generally decreases in our Tortonian run. As a consequence, the northward atmospheric heat transport is stronger in the Tortonian experiment. In northern mid-latitudes, the sensible and latent heat fluxes related to transient eddies increase compared to today. The stronger poleward transient eddy heat transport in the Tortonian model run correlates with intensified stormtracks in the mid-latitudes. In the palaeoclimate model run, the increased northward transient eddy heat transport together with the different-than-present land surface cover leads to a warming of polar regions and, hence, to a reduction of the meridional temperature gradient. The low elevation of Tibet in our palaeoclimate experiment causes a general weakening of the monsoon system in Asia. The E-Asian monsoon precipitation decreases compared to our reference run, but monsoon rainfall in India increases. When comparing the model results with quantitative terrestrial proxy data, we observe some discrepancies for some specific localities. However, the large patterns in our Tortonian run agree fairly well with the fossil record.

Model migrations: mobility and boundary crossings in regional climate prediction

by Mike Hulme

This paper written with PhD student Martin Mahony explores the 'movement' of climate models drawing upon theories from STS and geographies of science.

The Hadley Centre’s PRECIS regional climate modelling system has been designed to fulfil the informational... more The Hadley Centre’s PRECIS regional climate modelling system has been designed to fulfil the informational requirements of adaptation and development planners in the ‘global south’. Drawing on recent insights from science and technology studies and the geography of science concerning the mobility of scientific knowledge, this study investigates the institutional and discursive associations that enable the PRECIS modelling system to move between its UK birthplace and new sites of climate simulation. Document analysis and interviews with key personnel reveal the construction of regional climate modelling as an obligatory passage point for those seeking to adapt to future climates in developing countries. Furthermore, the operation of PRECIS across the boundaries of intersecting scientific and political worlds imbues the model with a level of epistemic power that has enabled the partial re-shaping of the global geographies of climate knowledge production. This new structuring of scientific practice is potentially empowering through the redistribution of climate modelling expertise, yet it may also contribute to the construction of climate prediction as a limit to adaptation. We argue that it furthers an epistemic hegemony that renders alternative ‘ways of knowing’ the climate either subordinate to or dependent upon the epistemic community centred on the Intergovernmental Panel on Climate Change and global governance mechanisms. The study illuminates the potential for geographers of science to make normative interventions in debates around the interplay of space, knowledge and power in contexts of environmental deliberation and governance.

Validity of Climate Change Forecasting for Public Policy Decision Making

by J Armstrong

Co-authored with Kesten C. Green and Willie Soon.

Policymakers need to know whether prediction is possible and if so whether any proposed forecasting method will... more Policymakers need to know whether prediction is possible and if so whether any proposed forecasting method will provide forecasts that are substantively more accurate than those from the relevant benchmark method. Inspection of global temperature data suggests that it is subject to irregular variations on all relevant time scales and that variations during the late 1900s were not unusual. In such a situation, a “no change” extrapolation is an appropriate benchmark forecasting method. We used the U.K. Met Office Hadley Centre’s annual average thermometer data from 1850 through 2007 to examine the performance of the benchmark method. The accuracy of forecasts from the benchmark is such that even perfect forecasts would be unlikely to help policymakers. For example, mean absolute errors for 20- and 50-year horizons were 0.18°C and 0.24°C. We nevertheless demonstrate the use of benchmarking with the example of the Intergovernmental Panel on Climate Change’s 1992 linear projection of long-term warming at a rate of 0.03°C-per-year. The small sample of errors from ex ante projections at 0.03°C-per-year for 1992 through 2008 was practically indistinguishable from the benchmark errors. Validation for long-term forecasting, however, requires a much longer horizon. Again using the IPCC warming rate for our demonstration, we projected the rate successively over a period analogous to that envisaged in their scenario of exponential CO2 growth—the years 1851 to 1975. The errors from the projections were more than seven times greater than the errors from the benchmark method. Relative errors were larger for longer forecast horizons. Our validation exercise illustrates the importance of determining whether it is possible to obtain forecasts that are more useful than those from a simple benchmark before making expensive policy decisions.

A global dynamic model for the Neolithic transition

by Carsten Lemmen

Co-authored with Kai W. Wirtz, published in Climatic Change 59, 333–367, 2003.

During the Holocene strong gradients in the distribution of technology including subsistence ways emerged on a global... more During the Holocene strong gradients in the distribution of technology including subsistence ways emerged on a global scale. These patterns were further amplified in historic times and are still visible through worldwide differences in national wealth. In order to evaluate major factors responsible for the shift from foraging to food production we here employ quantitative methods by developing a deterministic but simple model. After compiling existing maps of potential vegetation at 5000 BP the inhabited world is split into 197 regions with homogeneous environmental conditions. Suitable variables for the macro-economic and cultural development in the Neolithic period are found to be farming to hunting-gathering ratio, number of agricultural economies and a technological development index. The model explicitly describes economic adaptation, growth and migration of human populations together with the spread of their cultural characteristics; it accounts for over- exploitation of natural resources, crowding mortality and the climate variability on a millennium scale. In a thorough model validation region specific trajectories are compared to archaeological evidence revealing a high correspondence. Major parts of the known sequence of Neolithic centers including the timing differences are robustly reproduced. A series of known problems in prehistory is discussed comprising the lag between domestication and full scale farming, the off-leveling of the technological boost following the transition, the emergence of distinct migration waves and sensitiv- ity to climate fluctuations. Not mere population pressure but continuous innovation and competition between subsistence strategies is identified as a prime mover of agricultural development. The results suggest that few aspects of biogeography may have determined the observed continental gradients in the number of domesticable species ultimately leading to an increasing differentiation in technology and demography.

Modeling density dependence and climatic disturbances in caribou: a case study from the Bathurst Island complex, Canadian High Arctic

by Mike Ferguson

Tews J, Ferguson MAD, Fahrig L. 2007. Modeling density dependence and climatic disturbances in caribou: A case study from the Bathurst Island complex, Canadian high arctic. Journal of Zoology 272(2): 209-217.

Keywords: climate change; density independence; environmental stochasticity; Peary caribou; population dynamics; population viability analysis; simulation model

Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the... more Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the Canadian High Arctic. Because of severe population declines following years of unfavorable winter weather with ice coating on the ground or thicker snow cover, it is believed that density-independent disturbance events are the primary driver for Peary caribou population dynamics. However, it is unclear to what extent density dependence may affect population dynamics of this species. Here, we test for different levels of density dependence in a stochastic, single-stage population model, based on available empirical information for the Bathurst Island complex (BIC) population in the Canadian High Arctic. We compare predicted densities with observed densities during 1961–2001 under various assumptions of the strength of density dependence. On the basis of our model, we found that scenarios with no or very low density dependence led to population densities far above observed densities. For average observed disturbance regimes, a carrying capacity of 0.1 caribou km−2 generated an average caribou density similar to that estimated for the BIC population over the past four decades. With our model we also tested the potential effects of climate change-related increases in the probability and severity of disturbance years, that is unusually poor winter conditions. On the basis of our simulation results, we found that, in particular, potential increases in disturbance severity (as opposed to disturbance frequency) may pose a considerable threat to the persistence of this species.

Adaptive grids for weather and climate models

by Quentin F. Stout

Appears in ECMWF Proc. Recent Developments in Numerical Methods for Atmospheric and Climate Modeling (2004), pp. 233-250