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Climate Signal (climate + signal)
Selected AbstractsThe Interplay between Climate Variability and Density Dependence in the Population Viability of Chinook SalmonCONSERVATION BIOLOGY, Issue 1 2006RICHARD W. ZABEL análisis de viabilidad poblacional; especies en peligro; Oncorhynchus tshawytscha Abstract:,The viability of populations is influenced by driving forces such as density dependence and climate variability, but most population viability analyses (PVAs) ignore these factors because of data limitations. Additionally, simplified PVAs produce limited measures of population viability such as annual population growth rate (,) or extinction risk. Here we developed a "mechanistic" PVA of threatened Chinook salmon (Oncorhynchus tshawytscha) in which, based on 40 years of detailed data, we related freshwater recruitment of juveniles to density of spawners, and third-year survival in the ocean to monthly indices of broad-scale ocean and climate conditions. Including climate variability in the model produced important effects: estimated population viability was very sensitive to assumptions of future climate conditions and the autocorrelation contained in the climate signal increased mean population abundance while increasing probability of quasi extinction. Because of the presence of density dependence in the model, however, we could not distinguish among alternative climate scenarios through mean , values, emphasizing the importance of considering multiple measures to elucidate population viability. Our sensitivity analyses demonstrated that the importance of particular parameters varied across models and depended on which viability measure was the response variable. The density-dependent parameter associated with freshwater recruitment was consistently the most important, regardless of viability measure, suggesting that increasing juvenile carrying capacity is important for recovery. Resumen:,La viabilidad de poblaciones esta influida por fuerzas conductoras como la denso dependencia y la variabilidad climática, pero la mayoría de los análisis de viabilidad poblacional (AVP) ignoran estos factores debido a limitaciones en la disponibilidad de datos. Adicionalmente, los AVP simplificados producen medidas limitadas de la viabilidad poblacional tales como la tasa anual de crecimiento poblacional (,) o el riesgo de extinción. Aquí desarrollamos un AVP "mecanicista" de Oncorhynchus tshawytscha en el que, con base en datos detallados de 40 años, relacionamos el reclutamiento de juveniles en agua dulce con la densidad de reproductores, y la supervivencia en el océano al tercer año con índices mensuales de condiciones oceánicas y climáticas a amplia escala. La inclusión de la variabilidad climática en el modelo produjo efectos importantes: la viabilidad poblacional estimada fue muy sensible a las suposiciones de condiciones climáticas futuras y la autocorrelación contenida en la señal climática aumentó la abundancia poblacional promedio al mismo tiempo que incrementó la probabilidad de cuasi extinción. Sin embargo, debido a la presencia de denso densidad en el modelo no pudimos distinguir entre escenarios climáticos alternativos a través de los valores promedio de ,, lo que enfatiza la importancia de considerar medidas múltiples para dilucidar la viabilidad poblacional. Nuestros análisis de sensibilidad demostraron que la importancia de parámetros particulares varió en los modelos y dependió de la medida de viabilidad utilizada como variable de respuesta. El parámetro de denso dependencia asociada con el reclutamiento en agua dulce consistentemente fue el más importante, independientemente de la medida de viabilidad, lo que sugiere que el incremento en la capacidad de carga de juveniles es importante para la recuperación. [source] Temporal dynamics within a contemporary latitudinal diversity gradientECOLOGY LETTERS, Issue 9 2008Jonathan A. D. Fisher Abstract Poleward declines in species diversity [latitudinal diversity gradients (LDG)] remain among the oldest and most widespread of macroecological patterns. However, their contemporary dynamics remain largely unexplored even though changing ecological conditions, including global change, may modify LDG and their respective ecosystems. Here, we examine temporal variation within a temperate Northwest Atlantic LDG using 31 years of annual fisheries-independent surveys and explore its dynamics in relation to a dominant climate signal [the wintertime North Atlantic Oscillation (NAO)] that varies interannually and alters the latitudinal gradient of Northwest Atlantic continental shelf bottom water temperatures. We found that the slopes of the annual LDG vary dramatically due to changes in geographic distributions of 100+ species, variations that are concealed within the cumulative, static LDG. These changes are strongly associated with changes in NAO sign and strength. This is the first illustration of temporal dynamics in a contemporary LDG and the first demonstration of the speed at which local environmental variations can alter an LDG. Our findings underscore the need to investigate factors that modify LDG separately from those that contribute to their origins. [source] Large-scale climatic signatures in lakes across Europe: a meta-analysisGLOBAL CHANGE BIOLOGY, Issue 7 2007THORSTEN BLENCKNER Abstract Recent studies have highlighted the impact of the winter North Atlantic Oscillation (NAO) on water temperature, ice conditions, and spring plankton phenology in specific lakes and regions in Europe. Here, we use meta-analysis techniques to test whether 18 lakes in northern, western, and central Europe respond coherently to winter climate forcing, and to assess the persistence of the winter climate signal in physical, chemical, and biological variables during the year. A meta-analysis approach was chosen because we wished to emphasize the overall coherence pattern rather than individual lake responses. A particular strength of our approach is that time-series from each of the 18 lakes were subjected to the same robust statistical analysis covering the same 23-year period. Although the strongest overall coherence in response to the winter NAO was exhibited by lake water temperatures, a strong, coherent response was also exhibited by concentrations of soluble reactive phosphorus and soluble reactive silicate, most likely as a result of the coherent response exhibited by the spring phytoplankton bloom. Lake nitrate concentrations showed significant coherence in winter. With the exception of the cyanobacterial biomass in summer, phytoplankton biomass in all seasons was unrelated to the winter NAO. A strong coherence in the abundance of daphnids during spring can most likely be attributed to coherence in daphnid phenology. A strong coherence in the summer abundance of the cyclopoid copepods may have been related to a coherent change in their emergence from resting stages. We discuss the complex nature of the potential mechanisms that drive the observed changes. [source] ENSO history recorded in Agathis australis (kauri) tree rings.INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2008Part A: kauri's potential as an ENSO proxy Abstract Although many of the main characteristics of the El Niño-Southern Oscillation (ENSO) phenomenon have been established, uncertainties remain concerning its multidecadal- to millennial-scale evolution. Because of the shortness of the instrumental record, we need to resort to proxy-based reconstructions to investigate ENSO's history prior to the mid 19th century, but the available proxy data is limited in both time and space. Here we investigate the potential for ENSO reconstruction from the tree rings of Agathis australis (kauri). Kauri is a long-lived endemic New Zealand conifer and grows in an ENSO teleconnection region not previously represented in ENSO multi-proxy studies. A high quality 423 year kauri regional master chronology (AD 1580,2002) is constructed. Statistical analysis of the period AD 1876,2002 confirms previous findings that kauri tree rings carry a strong regional-scale climate signal and that ENSO is a significant contributor (predominantly via the western pole of the Southern Oscillation). Kauri carries a signal of both ENSO phases, but with a slight El Niño bias. Growth sensitivity is primarily registered through a five-season window, extending from March (prior to growth initiation in September) through to the following May, with strongest relationships across the middle three seasons (June,February). Relationships appear to be stationary. We conclude that kauri has sufficient ENSO event capture skill to make it a useful addition to future multi-proxy ENSO reconstruction efforts. It may also have potential for stand-alone reconstruction of multidecadal- to millennial-scale evolution of ENSO activity, especially ENSO robustness. Copyright © 2007 Royal Meteorological Society [source] Rapid Holocene climate changes in the North Atlantic: evidence from lake sediments from the Faroe IslandsBOREAS, Issue 1 2006CAMILLA S. ANDRESEN Holocene records from two lakes on the Faroe Islands were investigated to determine regional climatic variability: the fairly wind-exposed Lake Starvatn on Streymoy and the more sheltered Lake Lykkjuvötn on Sandoy. Sediment cores were analysed for content of biogenic silica, organic carbon and clastic material, and magnetic susceptibility. In addition, a new qualitative proxy for past lake ice cover and wind activity was developed using the flux of clastic grains that are larger than 255 ,m. Both long-term and short-term climatic developments were similar between the two lakes, suggesting a response to a regional climate signal. The long-term climate development is characterized by early Holocene rapid warming followed by Holocene climatic optimum conditions ending around 8300 cal. yr BP. A more open landscape as evidenced from increased sand grain influx in the period 8300,7200 cal. yr BP could reflect the aftermath of the 8200 cal. yr BP event, although the event itself is not recognized in either of the two lake records. From around 7200 cal. yr BP the mid-Holocene climate deterioration is observed and from 4200 cal. yr BP the climate deteriorated further with increased amplitude of centennial cooling episodes. [source] ALPINE AREAS IN THE COLORADO FRONT RANGE AS MONITORS OF CLIMATE CHANGE AND ECOSYSTEM RESPONSE,GEOGRAPHICAL REVIEW, Issue 2 2002MARK W. WILLIAMS ABSTRACT. The presence of a seasonal snowpack in alpine environments can amplify climate signals. A conceptual model is developed for the response of alpine ecosystems in temperate, midlatitude areas to changes in energy, chemicals, and water, based on a case study from Green Lakes Valley,Niwot Ridge, a headwater catchment in the Colorado Front Range. A linear regression shows the increase in annual precipitation of about 300 millimeters from 1951 to 1996 to be significant. Most of the precipitation increase has occurred since 1967. The annual deposition of inorganic nitrogen in wetfall at the Niwot Ridge National Atmospheric Deposition Program site roughly doubled between 1985,1988 and 1989,1992. Storage and release of strong acid anions, such as those from the seasonal snowpack in an ionic pulse, have resulted in episodic acidification of surface waters. These biochemical changes alter the quantity and quality of organic matter in high-elevation catchments of the Rocky Mountains. Affecting the bottom of the food chain, the increase in nitrogen deposition may be partly responsible for the current decline of bighorn sheep in the Rocky Mountains. [source] The Effects of Weather and Climate on the Seasonality of Influenza: What We Know and What We Need to KnowGEOGRAPHY COMPASS (ELECTRONIC), Issue 7 2010Christopher Fuhrmann Influenza is one of the most deadly of all airborne and upper-respiratory infections. On average, 22,000 deaths and over 3 million hospitalizations in USA are attributed to influenza each year. The distinct seasonality of influenza suggests a climate connection, but the wide range of methodologies used to explore this connection makes it difficult to elucidate a definitive relationship. Much of what is known about the effects of weather and climate on the seasonality of influenza stems from research conducted by members of the public health and medical communities, with few contributions from other physical and social science fields. Most of these studies are either based on experiments conducted under controlled laboratory conditions or on the broad-scale patterns of morbidity and mortality and their relationship to large-scale climate signals. What remains largely unknown is the suitability of these results for the development of early warning systems and for determining the dynamics of viral transmission on multiple space and time scales. [source] Performance of statistical downscaling models in GCM validation and regional climate change estimates: application for Swedish precipitationINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2001Aristita Busuioc Abstract This study deals with an analysis of the performance of a general circulation model (GCM) (HadCM2) in reproducing the large-scale circulation mechanisms controlling Swedish precipitation variability, and in estimating regional climate changes owing to increased CO2 concentration by using canonical correlation analysis (CCA). Seasonal precipitation amounts at 33 stations in Sweden over the period 1899,1990 are used. The large-scale circulation is represented by sea level pressure (SLP) over the Atlantic,European region. The link between seasonal Swedish precipitation and large-scale SLP variability is strong in all seasons, but especially in winter and autumn. For these two seasons, the link is a consequence of the North Atlantic Oscillation (NAO) pattern. In winter, another important mechanism is related to a cyclonic/anticyclonic structure centred over southern Scandinavia. In the past century, this connection has remained almost unchanged in time for all seasons except spring. The downscaling model that is built on the basis of this link is skilful in all seasons, but especially so in winter and autumn. This observed link is only partially reproduced by the HadCM2 model, while large-scale SLP variability is fairly well reproduced in all seasons. A concept about optimum statistical downscaling models for climate change purposes is proposed. The idea is related to the capability of the statistical downscaling model to reproduce low frequency variability, rather than having the highest skill in terms of explained variance. By using these downscaling models, it was found that grid point and downscaled climate signals are similar (increasing precipitation) in summer and autumn, while in winter, the amplitudes of the two signals are different. In spring, both signals show a slight increase in the northern and southern parts of Sweden. Copyright © 2001 Royal Meteorological Society [source] Joint projections of temperature and precipitation change from multiple climate models: a hierarchical Bayesian approachJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2009Claudia Tebaldi Summary., Posterior distributions for the joint projections of future temperature and precipitation trends and changes are derived by applying a Bayesian hierachical model to a rich data set of simulated climate from general circulation models. The simulations that are analysed here constitute the future projections on which the Intergovernmental Panel on Climate Change based its recent summary report on the future of our planet's climate, albeit without any sophisticated statistical handling of the data. Here we quantify the uncertainty that is represented by the variable results of the various models and their limited ability to represent the observed climate both at global and at regional scales. We do so in a Bayesian framework, by estimating posterior distributions of the climate change signals in terms of trends or differences between future and current periods, and we fully characterize the uncertain nature of a suite of other parameters, like biases, correlation terms and model-specific precisions. Besides presenting our results in terms of posterior distributions of the climate signals, we offer as an alternative representation of the uncertainties in climate change projections the use of the posterior predictive distribution of a new model's projections. The results from our analysis can find straightforward applications in impact studies, which necessitate not only best guesses but also a full representation of the uncertainty in climate change projections. For water resource and crop models, for example, it is vital to use joint projections of temperature and precipitation to represent the characteristics of future climate best, and our statistical analysis delivers just that. [source] | ||||||||||||||||