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Warming Trend (warming + trend)
Selected AbstractsSpecies interaction and response to wind speed alter the impact of projected temperature change in a montane ecosystemJOURNAL OF VEGETATION SCIENCE, Issue 4 2010Dafydd Crabtree Abstract Question: How does an improved understanding of species interactions, combined with an additional ecological variable (wind speed), alter the projected vegetation response to variation in altitudinal temperature? Location: Cairngorm Mountains, Scotland. Methods: Montane heathland vegetation was sampled from 144 plots (432 quadrats) comprising eight altitudinal transects. Ordination by partial DCA and path analysis was used to confirm: (1) the effect of wind speed and altitude (, temperature) on vegetation structure, i.e. canopy height and cover of bare ground, and (2) the control of arctic/alpine macrolichen occurrence by vegetation structure. Nested regression analysis was used to project the response of vegetation structure and lichen occurrence to temperature change scenarios with and without a step-wise change in future wind speed. Results: Warming trends shifted vegetation zones upwards, with a subsequent loss of suitable habitat for arctic/alpine lichens. However, incorporating wind speed as an additional explanatory variable had an important modifying effect on the vegetation response to temperature: decreasing wind speed exaggerates the effects of increased temperature and vice versa. Our models suggest that for the wind-driven heath examined, a 20% increase in mean wind speed may negate the effect of increased temperature on vegetation structure, resulting in no net change in lichen occurrence. Conclusions: We caution that an improved understanding of species interactions in vegetation response models may force the consideration of locally variable environmental parameters (e.g. wind speed), bringing into question the predicted vegetation response based on standard projections of temperature change along altitudinal gradients. [source] El Niño, climate change, and Southern African climateENVIRONMETRICS, Issue 4 2001Simon J. Mason Abstract The El Niño phenomenon involves a large-scale warming of the equatorial eastern and central Pacific Ocean. Recent developments in the El Niño,Southern Oscillation (ENSO) phenomenon have raised concerns about climate change. In this review paper, these recent developments are critically assessed and forecasts of possible future changes are reviewed. Since the late-1970s, El Niño episodes have been unusually recurrent, while the frequency of strong La Niña events has been low. Prolonged/recurrent warm event conditions of the first half of the 1990s were the result of the persistence of an anomalously warm pool near the date line, which, in turn, may be part of an abrupt warming trend in tropical sea-surface temperatures that occurred in the late-1970s. The abrupt warming of tropical sea-surface temperatures has been attributed to the enhanced-greenhouse effect, but may be indicative of inter-decadal variability: earlier changes in the frequency of ENSO events and earlier persistent El Niño and La Niña sequences have occurred. Most forecasts of ENSO variability in a doubled-CO2 climate suggest that the recent changes in the tropical Pacific are anomalous. Of potential concern, however, is a possible reduction in the predictability of ENSO events given a warmer background climate. El Niño events usually are associated with below-normal rainfall over much of southern Africa. Mechanisms for this influence on southern African climate are discussed, and the implications of possible changes in ENSO variability on the climate of the region are assessed. Recent observed changes in southern African climate and their possible relationships with trends in ENSO variability are investigated. The El Niño influence on rainfall over southern Africa occurs largely because of a weakening of tropical convection over the subcontinent. A warming of the Indian Ocean during El Niño events appears to be important in providing a teleconnection from the equatorial Pacific Ocean. The abrupt warming of the tropical Pacific and Indian oceans in the late-1970s is probably partly responsible for increasing air temperatures over southern Africa, and may have contributed to a prolongation of predominantly dry conditions. A return to a wet phase appears to have occurred, despite the persistence of anomalously high sea-surface temperatures associated with the late-1970s warming, and a record-breaking El Niño in 1997/98. Copyright © 2001 John Wiley & Sons, Ltd. [source] Spatial and temporal variability of the Aleutian climateFISHERIES OCEANOGRAPHY, Issue 2005SERGEI N. RODIONOV Abstract The objective of this paper is to highlight those characteristics of climate variability that may pertain to the climate hypothesis regarding the long-term population decline of Steller sea lions (Eumetopias jubatus). The seasonal changes in surface air temperature (SAT) across the Aleutian Islands are relatively uniform, from 5 to 10°C in summer to near freezing temperatures in winter. The interannual and interdecadal variations in SAT, however, are substantially different for the eastern and western Aleutians, with the transition found at about 170°W. The eastern Aleutians experienced a regime shift toward a warmer climate in 1977, simultaneously with the basin-wide shift in the Pacific Decadal Oscillation (PDO). In contrast, the western Aleutians show a steady decline in winter SATs that started in the 1950s. This cooling trend was accompanied by a trend toward more variable SAT, both on the inter- and intra-annual time scale. During 1986,2002, the variance of winter SATs more than doubled compared to 1965,1985. At the same time in Southeast Alaska, the SAT variance diminished by half. Much of the increase in the intra-seasonal variability for the western Aleutians is associated with a warming trend in November and a cooling trend in January. As a result, the rate of seasonal cooling from November to January has doubled since the late 1950s. We hypothesize that this trend in SAT variability may have increased the environmental stress on the western stock of Steller sea lions and hence contributed to its decline. [source] Mass mortality in Northwestern Mediterranean rocky benthic communities: effects of the 2003 heat waveGLOBAL CHANGE BIOLOGY, Issue 5 2009J. GARRABOU Abstract Late in summer 2003, extensive mass mortality of at least 25 rocky benthic macro-invertebrate species (mainly gorgonians and sponges) was observed in the entire Northwestern (NW) Mediterranean region, affecting several thousand kilometers of coastline. We were able to characterize the mortality event by studying six areas covering the main regions of the NW Mediterranean basin. The degree of impact on each study area was quantified at 49 sites by estimating the proportion of colonies affected in populations of several gorgonian species compared with reference data obtained in years without mortality signs. According to these data, the western areas (Catalan coast and Balearic Islands) were the least affected, while the central areas (Provence coast and Corsica-Sardinia) showed a moderate impact. The northernmost and eastern areas (Gulf of Genoa and Gulf of Naples) displayed the highest impact, with almost 80% of gorgonian colonies affected. The heat wave of 2003 in Europe caused an anomalous warming of seawater, which reached the highest temperatures ever recorded in the studied regions, between 1 and 3 °C above the climatic values (mean and maximum). Because this exceptional warming was observed in the depth ranges most affected by the mortality, it seems likely that the 2003 anomalous temperature played a key role in the observed mortality event. A correlation analysis between temperature conditions and degree of impact seems to support this hypothesis. Under the present climate warming trend, new mass mortality events may occur in the near future, possibly driving a major biodiversity crisis in the Mediterranean Sea. [source] Climate warming and the evolution of morphotypes in a reptileGLOBAL CHANGE BIOLOGY, Issue 2 2009VIRGINIE LEPETZ Abstract Climate warming is known to have effects on population dynamics through variations in survival, fecundity and density. However, the impacts of climate change on population composition are still poorly documented. Morphotypes are powerful markers to track changes in population composition. In the common lizard, Lacerta vivipara, individuals display two types of dorsal patterns: reticulated (R individuals) and linear (L individuals). We examined how local warming affected intrapopulation frequencies of these morphotypes across 11 years. We observed changes in morph frequency of dorsal patterns across years, paralleling the rise of spring temperatures. The proportion of R individuals increased with June temperatures in juveniles, yearlings, and adult males and females. Three mechanisms could explain these changes: phenotypic plasticity, microevolution and/or dispersal between populations. We investigated the ontogenetic determinism, fitness and recruitment rates associated with dorsal morphotypes. Dorsal pattern ontogeny showed temperature dependence but this relationship was not associated with the warming trend during this study. We found variation by morphotype in survival and clutch size, but these factors did not explain R frequency increases. Among all the parameters considered in this study, only a decrease of immigration, which was more pronounced in the L morphotype, could explain the change in population composition. To our knowledge, this provides the first evidence of the impact of climate warming on population composition due to its effects on immigration. [source] Climate warming causes phenological shift in Pink Salmon, Oncorhynchus gorbuscha, behavior at Auke Creek, AlaskaGLOBAL CHANGE BIOLOGY, Issue 2 2008SIDNEY G. TAYLORArticle first published online: 23 NOV 200 Abstract Thirty-four years (1972,2005) of water temperature data and extensive biological observations at Auke Creek, Alaska indicate a general warming trend that affected the native pink salmon (Oncorhynchus gorbuscha) population. Serial environmental records at nearby Auke Bay, Alaska over 46 years show trends of increasing air and sea surface temperatures. Trends of increased total precipitation and earlier date of ice out on nearby Auke Lake also occurred, but not at significant rates. Average water temperatures during the incubation of pink salmon in Auke Creek increased at a rate of 0.03 °C yr,1 over the 34-year period. For the 1972,2005 broods, midpoints of fry migrations from Auke Creek ranged between April 2 and May 7, and there was a trend of earlier migration of pink salmon fry at a rate of , 0.5 days yr,1. The migration timing of adult salmon into Auke Creek also showed a trend toward earlier timing. The earlier adult migration combined with warmer incubation temperatures are related to earlier migration of pink salmon fry. If the observed warming trend continues, Auke Creek may become unsuitable habitat for pink salmon. Given the trend for salmon fry to migrate earlier, a larger portion of the population may become mismatched with optimum environmental conditions during their early marine life history. If salmon adults continue to migrate into the creek earlier when water temperatures are commonly high, it will result in increased prespawning mortality. [source] Alteration of the food web along the Antarctic Peninsula in response to a regional warming trendGLOBAL CHANGE BIOLOGY, Issue 12 2004Mark A. Moline Abstract In the nearshore coastal waters along the Antarctic Peninsula, a recurrent shift in phytoplankton community structure, from diatoms to cryptophytes, has been documented. The shift was observed in consecutive years (1991,1996) during the austral summer and was correlated in time and space with glacial melt-water runoff and reduced surface water salinities. Elevated temperatures along the Peninsula will increase the extent of coastal melt-water zones and the seasonal prevalence of cryptophytes. This is significant because a change from diatoms to cryptophytes represents a marked shift in the size distribution of the phytoplankton community, which will, in turn, impact the zooplankton assemblage. Cryptophytes, because of their small size, are not grazed efficiently by Antarctic krill, a keystone species in the food web. An increase in the abundance and relative proportion of cryptophytes in coastal waters along the Peninsula will likely cause a shift in the spatial distribution of krill and may allow also for the rapid asexual proliferation of carbon poor gelatinous zooplankton, salps in particular. This scenario may account for the reported increase in the frequency of occurrence and abundance of large swarms of salps within the region. Salps are not a preferred food source for organisms that occupy higher trophic levels in the food web, specifically penguins and seals, and thus negative feedbacks to the ecology of these consumers can be anticipated as a consequence of shifts in phytoplankton community composition. [source] Interpreting variability in global SST data using independent component analysis and principal component analysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2010Seth Westra Abstract Component extraction techniques are used widely in the analysis and interpretation of high-dimensional climate datasets such as global sea surface temperatures (SSTs). Principal component analysis (PCA), a frequently used component extraction technique, provides an orthogonal representation of the multivariate dataset and maximizes the variance explained by successive components. A disadvantage of PCA, however, is that the interpretability of the second and higher components may be limited. For this reason, a Varimax rotation is often applied to the PCA solution to enhance the interpretability of the components by maximizing a simple structure. An alternative rotational approach is known as independent component analysis (ICA), which finds a set of underlying ,source signals' which drive the multivariate ,mixed' dataset. Here we compare the capacity of PCA, the Varimax rotation and ICA in explaining climate variability present in globally distributed SST anomaly (SSTA) data. We find that phenomena which are global in extent, such as the global warming trend and the El Niño-Southern Oscillation (ENSO), are well represented using PCA. In contrast, the Varimax rotation provides distinct advantages in interpreting more localized phenomena such as variability in the tropical Atlantic. Finally, our analysis suggests that the interpretability of independent components (ICs) appears to be low. This does not diminish the statistical advantages of deriving components that are mutually independent, with potential applications ranging from synthetically generating multivariate datasets, developing statistical forecasts, and reconstructing spatial datasets from patchy observations at multiple point locations. Copyright © 2009 Royal Meteorological Society [source] Changes in temperature extremes over Italy in the last 44 yearsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2008Andrea Toreti Abstract Changes in temperature extremes over Italy from 1961 to 2004 were evaluated on the basis of minimum and maximum temperatures measured by 49 synoptic stations uniformly distributed over the country. A set of extreme temperature indices of the Commission for Climatology/Climate Variability and Predictability (CCl/CLIVAR) Working Group on Climate Change Detection was calculated and statistically analysed in order to detect the presence of trends and quantify the variations of the indices for different time periods. Most of the indices, averaged over all stations, show a cooling trend until the end of the 1970s followed by a more pronounced warming trend in the last 25 years. The net variation of the indices reflects an increase in the extremes of the temperature distribution. Among the most significant results, an average increase of 12.3 summer days and 12.4 tropical nights in the overall 44 years are estimated. No significant differences between northern, central and southern Italy are found for most indices, indicating that the trends originate from large-scale climate features; however, the largest increase of tropical nights is observed at coastal stations. Copyright © 2007 Royal Meteorological Society [source] Modelling current trends in Northern Hemisphere temperaturesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2006Terence C. Mills Abstract Fitting a trend is of interest in many disciplines, but it is of particular importance in climatology, where estimating the current and recent trend in temperature is thought to provide a major indication of the presence of global warming. A range of ad hoc methods of trend fitting have been proposed, with little consensus as to the most appropriate techniques to use. The aim of this paper is to consider a range of trend extraction techniques, none of which require ,padding' out the series beyond the end of the available observations, and to use these to estimate the trend of annual mean Northern Hemisphere (NH) temperatures. A comparison of the trends estimated by these methods thus provides a robust indication of the likely range of current trend temperature increases and hence inform, in a timely quantitative fashion, arguments based on global temperature data concerning the nature and extent of global warming and climate change. For the complete sample 1856,2003, the trend is characterised as having long waves about an underlying increasing level. Since around 1970, all techniques display a pronounced warming trend. However, they also provide a range of trend functions so that extrapolation far into the future would be a hazardous exercise. Copyright © 2006 Royal Meteorological Society. [source] Solar-induced and internal climate variability at decadal time scalesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2005Mihai Dima Abstract Statistical analyses of long-term instrumental and proxy data emphasize a distinction between two quasi-decadal modes of climate variability. One mode is linked to atmosphere,ocean interactions (,the internal mode') and the other one is associated with the solar sunspots cycle (,the solar mode'). The distinct signatures of these two modes are also detected in a high-resolution sediment core located in the Cariaco basin. In the oceanic surface temperature the internal mode explains about three times more variance than the solar mode. In contrast, the solar mode dominates over the internal mode in the sea-level pressure and upper atmospheric fields. The heterogeneous methods and data sets used in this study underline the distinction between these decadal modes and enable estimation of their relative importance. The distinction between these modes is important for the understanding of climate variability, the recent global warming trend and the interpretation of high-resolution proxy data. Copyright © 2005 Royal Meteorological Society [source] Antarctic climate change during the last 50 yearsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2005John Turner Abstract An erratum has been published for this article in International Journal of Climatology 25 (8) 2005, 1147,1148. The Reference Antarctic Data for Environmental Research (READER) project data set of monthly mean Antarctic near-surface temperature, mean sea-level pressure (MSLP) and wind speed has been used to investigate trends in these quantities over the last 50 years for 19 stations with long records. Eleven of these had warming trends and seven had cooling trends in their annual data (one station had too little data to allow an annual trend to be computed), indicating the spatial complexity of change that has occurred across the Antarctic in recent decades. The Antarctic Peninsula has experienced a major warming over the last 50 years, with temperatures at Faraday/Vernadsky station having increased at a rate of 0.56 °C decade,1 over the year and 1.09 °C decade,1 during the winter; both figures are statistically significant at less than the 5% level. Overlapping 30 year trends of annual mean temperatures indicate that, at all but two of the 10 coastal stations for which trends could be computed back to 1961, the warming trend was greater (or the cooling trend less) during the 1961,90 period compared with 1971,2000. All the continental stations for which MSLP data were available show negative trends in the annual mean pressures over the full length of their records, which we attribute to the trend in recent decades towards the Southern Hemisphere annular mode (SAM) being in its high-index state. Except for Halley, where the trends are constant, the MSLP trends for all stations on the Antarctic continent for 1971,2000 were more negative than for 1961,90. All but two of the coastal stations have recorded increasing mean wind speeds over recent decades, which is also consistent with the change in the nature of the SAM. Copyright © 2005 Royal Meteorological Society [source] Trend and variability of China precipitation in spring and summer: linkage to sea-surface temperaturesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2004Fanglin Yang Abstract Observational records in the past 50 years show an upward trend of boreal-summer precipitation over central eastern China and a downward trend over northern China. During boreal spring, the trend is upward over southeastern China and downward over central eastern China. This study explores the forcing mechanism of these trends in association with the global sea-surface temperature (SST) variations on the interannual and interdecadal time scales. Results based on singular value decomposition (SVD) analyses show that the interannual variability of China precipitation in boreal spring and summer can be well defined by two centres of action for each season, which are covarying with two interannual modes of SSTs. The first SVD modes of precipitation in spring and summer, which are centred in southeastern China and northern China respectively, are linked to an El Niño,southern oscillation (ENSO)-like mode of SSTs. The second SVD modes of precipitation in both seasons are confined to central eastern China, and are primarily linked to SST variations over the warm pool and the Indian Ocean. Features of the anomalous 850 hPa winds and 700 hPa geopotential height corresponding to these modes support a physical mechanism that explains the causal links between the modal variations of precipitation and SSTs. On the decadal and longer time scale, similar causal links are found between the same modes of precipitation and SSTs, except for the case of springtime precipitation over central eastern China. For this case, while the interannual mode of precipitation is positively correlated with the interannual variations of SSTs over the warm pool and Indian Ocean, the interdecadal mode is negatively correlated with a different SST mode, i.e. the North Pacific mode. The latter is responsible for the observed downward trend of springtime precipitation over central eastern China. For all other cases, both the interannual and interdecadal variations of precipitation can be explained by the same mode of SSTs. The upward trend of springtime precipitation over southeastern China and downward trend of summertime precipitation over northern China are attributable to the warming trend of the ENSO-like mode. The recent frequent summertime floods over central eastern China are linked to the warming trend of SSTs over the warm pool and Indian Ocean. Copyright © 2004 Royal Meteorological Society [source] Changes in Antarctic Peninsula tropospheric temperatures from 1956 to 1999: a synthesis of observations and reanalysis dataINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2002Gareth J. Marshall Abstract The surface warming at Faraday station in the western Antarctic Peninsula is one of the largest observed anywhere over the last 50 years, yet the physical mechanisms driving this climate change are poorly understood. In this paper we synthesize radiosonde temperature observations from three Peninsula stations and NCEP,NCAR reanalysis data in order to examine contemporaneous regional tropospheric temperature trends (1956,99), which may in turn help us to understand better the causes of the surface warming. The reanalysis data are utilized in two ways: (i) to provide long-term mean monthly offsets between Faraday, which ceased radiosonde observations in 1982, and two other stations in the region having more recent data, Bellingshausen and Marambio, in order to create post-1982 simulated Faraday data; (ii) after having any spurious trends and bias removed, to provide directly a monthly value for Faraday when no equivalent value from regional observations is available. Using available months of overlap, a comparison between temperature observations and simulated data suggests that the latter are a reasonable facsimile of the former. The synthesized time-series of tropospheric temperatures reveal a statistically significant mean annual tropospheric (850,300 hPa) warming above Faraday between 1956 and 1999 of ,0.027±0.022 °C year,1. Winter and summer both show a warming trend, with significance varying with height and season. Annually, the mean tropospheric warming is half that at the surface, Unlike the surface warming, the calculated tropospheric warming trend is no greater than observed at other Antarctic stations, and indeed is not significantly greater than the background global warming trend for most of the period examined. Thus, we cannot dismiss the possibility that the Peninsula surface warming may simply be a response to a global warming magnified by the observed strong regional feedback between sea-ice extent and surface temperature during winter. Copyright © 2002 Royal Meteorological Society. [source] Disaggregating climatic trends by classification of circulation patternsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2001Radan Huth Abstract The trends in occurrence frequencies of circulation types over Europe and in nine climate variables in the Czech Republic conditioned by the types are examined for period 1949,1980. The circulation types are determined by an objective procedure from daily 500 hPa heights. Both in summer and winter, anticyclonic types have become more frequent at the expense of cyclonic types. The circulation changes are shown to be unrelated to the trends in surface climate elements in summer, whereas in winter, trends in circulation explain a part of the observed warming and strengthening of southerly winds. The trends in climate elements are not uniform among circulation types. In summer, the trend pattern consisting of decreasing maximum and daily mean temperatures, daily temperature range (DTR) and sunshine duration, and increasing cloudiness and relative humidity is observed under the cyclonic types and the types with a well-pronounced jet, but is missing under types with a blocking anticyclone over Europe. Two possible mechanisms causing this trend pattern are proposed: increasing cloudiness, and a process responsible for the reduction of sunshine without a concurrent increase of cloudiness. The latter mechanism can possibly be identified with increasing aerosol concentrations. In winter, the degree of warming is governed by changes in zonal wind. The mechanism of change in DTR seems to vary with elevation: at the lowland station (Prague-Klementinum), the increase in DTR is related to the warming trend, and consequently with zonal wind changes, while at the mountain station (Mile,ovka), the increase in DTR reflects the increase in precipitating clouds. The changes in DTR are related much more to mid-tropospheric circulation than to cloud cover in summer, whereas in winter, cloud cover plays a more important role in affecting DTR trends. Copyright © 2001 Royal Meteorological Society [source] A review of changes in the fish assemblages of Levantine inland and marine ecosystems following the introduction of non-native fishesJOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2005M. Goren Summary The arrival of non-native fishes in the Levant Basin began in the late 19th century. Whereas the presence of most of the 40 non-native freshwater fishes stem from intentional introductions, either for aquaculture or pest control, the 62 species of non-native marine fishes arrived by natural dispersal via the Suez Canal. Of the non-native freshwater species, five have established successful breeding populations (mosquitofish Gambusia affinis, common carp Cyprinus carpio, crucian carp Carassius carassius, swordtail Xiphophorus hellerii and rainbow trout Oncorhynchus mykiss), and seven are regularly stocked in natural habitats (thinlip mullet Liza ramada, flathead mullet Mugil cephalus, European eel Anguilla anguilla, grass carp Ctenopharyngodon idella, Asian silver carp Hypophthalmichthys molitrix, bighead carp Aristichthys nobilis, black carp Mylopharyngodon piceus). Some non-native species appear to have out-competed native species. Gambusia affinis may have caused the extirpation of two native cyprinid fishes from the Qishon River basin (Levant silver carp Hemigrammocapoeta nana and common garra Garra rufa) and the southern Dead Sea (endemic Sodom's garra G. ghoerensis). The opening of the Suez Canal in 1869 allowed entry into the eastern Mediterranean of Indo-Pacific and Erythrean biota, with the latter now dominating the community structure (50,90% of fish biomass) and function (altered native food web) of the Levantine littoral and infra-littoral zones. The process has accelerated in recent years concurrent with a warming trend of the seawater. Record numbers of newly discovered non-native species is leading to the creation of a human-assisted Erythrean biotic province in the eastern Mediterranean. [source] Biogeography of the nearshore rocky-reef fishes at the southern and Baja California islandsJOURNAL OF BIOGEOGRAPHY, Issue 2 2005Daniel J. Pondella II Abstract Aim, To examine the uniqueness and relationship of islands in the San Diegan Province using reef fishes. Location, Pacific coast of Baja and Southern California. Methods, Quantitative scuba surveys and statistics were used. Between June 2000 and August 2002, the nearshore rocky-reef fishes of eight southern California and Baja California islands were quantitatively surveyed. The islands surveyed were: Santa Cruz, San Nicolas, Santa Barbara, Santa Catalina, San Clemente, North Coronado, San Martin and San Benito. These islands span the latitudinal range of offshore islands within the San Diegan marine province. This regional scale approach provided not only the first quantitative description of rocky-reef fishes at five of these islands, but also allowed comparisons with known biogeographical patterns. Results, Here we discuss the distribution and abundance of 84 conspicuous rocky-reef fishes from 35 families. In general, the richness, diversity and composition of fish assemblages at these islands were found to reflect previously described biogeographical processes. The rocky reef fish assemblages of all islands in the survey were found to be significantly distinctive form each other. Phenetic analyses revealed two clusters. San Clemente, Santa Catalina and North Coronado clustered as a warm-water assemblage in the middle of the San Diegan Province. The remaining islands grouped together as a cold-water assemblage, despite the geographically disjunct position of the islands within this cluster. The relatedness of islands was independent of distance. Examination of the most common fish species at all islands revealed that while some conformed to the north,south trending density distributions predicted by previous investigators, the distribution of others could not be explained by latitude or temperature regimes. No single pattern explained the density of fishes at all islands. Both the rock croaker, Pareques sp., and flag cabrilla, Epinephelus labriformis, were observed at San Benito during these surveys, representing northern range extensions and may be indicators of the warming trend observed in this marine province. Main conclusion, For nearshore rocky-reef fishes, the islands of the San Diegan marine province are distinct and their interrelatedness is independent of the distance between them. [source] The effect of transient conditions on an equilibrium permafrost-climate modelPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2007Dan Riseborough Abstract Equilibrium permafrost models assume a stationary temperature and snow-cover climate. With a variable or changing climate, short-term energy imbalances between the active layer and permafrost result in transient departures from the equilibrium condition. This study examines the effects of such variability on an equilibrium permafrost-climate model, the temperature at the top of permafrost (TTOP) model. Comparisons between numerical results and temperatures predicted by the TTOP-model suggest that stationary inter-annual variability introduces an error in the top-of-permafrost temperature obtained with the equilibrium model that is higher where permafrost temperature is close to 0°C, although multi-year averaging reduces the error to 0.1°C or less. In the presence of a warming trend, the equilibrium model prediction tracked the changing top-of-permafrost temperature until permafrost temperatures reached 0°C, after which the equilibrium model produced significant errors. Errors up to 1°C were due to the temperature gradient through the developing talik, and depended on the warming rate, and the thickness of the talik. For all warming rates, the error was largest when the permafrost table was about 4,m below the surface, with the error declining as the permafrost table fell. Copyright © 2007 John Wiley & Sons, Ltd. [source] Palaeoclimate reconstruction on Big Lyakhovsky Island, north Siberia,hydrogen and oxygen isotopes in ice wedgesPERMAFROST AND PERIGLACIAL PROCESSES, Issue 2 2002Hanno Meyer Abstract Late Quaternary permafrost deposits on Big Lyakhovsky Island (New Siberian Islands, Russian Arctic) were studied with the aim of reconstructing the palaeoclimatic and palaeoenvironmental conditions of northern Siberia. Hydrogen and oxygen stable isotope analyses are presented for six different generations of ice wedges as well as for recent ice wedges and precipitation. An age of about 200 ka BP was determined for an autochtonous peat layer in ice-rich deposits by U/Th method, containing the oldest ice wedges ever analysed for hydrogen and oxygen isotopes. The palaeoclimatic reconstruction revealed a period of severe winter temperatures at that time. After a gap in the sedimentation history of several tens of thousands of years, ice-wedge growth was re-initiated around 50 ka BP by a short period of extremely cold winters and rapid sedimentation leading to ice-wedge burial and characteristic ice-soil wedges (,polosatics'). This corresponds to the initial stage for the Late Weichselian Ice Complex, a peculiar cryolithogenic periglacial formation typical of the lowlands of northern Siberia. The Ice Complex ice wedges reflect cold winters and similar climatic conditions as around 200 ka BP. With a sharp rise in ,18O of 6, and ,D of 40,, the warming trend between Pleistocene and Holocene ice wedges is documented. Stable isotope data of recent ice wedges show that Big Lyakhovsky Island has never been as warm in winter as today. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of ENSO on the Hong Kong winter seasonATMOSPHERIC SCIENCE LETTERS, Issue 2 2009M. C. Wu Abstract The relationship between the ENSO condition and the winter condition in Hong Kong is investigated in this study. The winter monsoon over southern China tends to be weaker (stronger) during El Niño (La Niña) winters and Hong Kong tends to have higher (lower) mean winter temperatures against the background of the warming trend. On the other hand, there are more (fewer) surge events, which represents the southeastward advance of the Siberian cold air across the East Asian coast, affecting Hong Kong. Analyses showed that Hong Kong tends to be warmer with a shorter duration for the longest cold spell during the winter without blocking event over the Eurasian continent. Furthermore, blocking events are also less common during El Niño winters. Copyright © 2009 Royal Meteorological Society [source] Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic OceanBOREAS, Issue 1 2001JEAN-CLAUDE DUPLESSY Foraminiferal assemblages were studied in northern Barents Sea core ASV 880 along with oxygen and carbon isotope measurements in planktonic (N. pachyderma sin.) and benthic (E clavatum) species. AMS C-14 measurements performed on molluscs Yoldiella spp. show that this core provides a detailed and undisturbed record of Holocene climatic changes over the last 10000 calendar years. Surface and deep waters were very cold (<0°C) at the beginning of the Holocene. C. reniforme dominated the highly diverse benthic foraminiferal assemblage. From 10 to 7.8 cal. ka BP, a warming trend culminated in a temperature optimum, which developed between 7.8 and 6.8 cal. ka BP. During this optimum, the input of Atlantic water to the Barents Sea reached its maximum. The Atlantic water mass invaded the whole Franz Victoria Trough and was present from subsurface to the bottom. No bottom water, which would form through rejection of brine during winter, was present at the core depth (388 m). The water stratification was therefore greatly reduced as compared to the present. An increase in percentage of I. helenae/norcrossi points to long seasonal ice-free conditions. The temperature optimum ended rather abruptly, with the return of cold polar waters into the trough within a few centuries. This was accompanied by a dramatic reduction of the abundance of C. reniforme. During the upper Holocene, the more opportunistic species E. clavatum became progressively dominant and the water column was more stratified. Deep water in Franz Victoria Trough contained a significant amount of cold Barents Sea bottom water as it does today, while subsurface water warmed progressively until about 3.7 cal. ka BP and reached temperatures similar to those of today. These long-term climatic changes were cut by several cold events of short duration, in particular one in the middle of the temperature optimum and another, which coincides most probably with the 8.2 ka BP cold event. Both long- and short-term climatic changes in the Barents Sea are associated with changes in the flow of Atlantic waters and the oceanic conveyor belt. [source] Hemispheric-scale patterns of climate-related shifts in planktonic diatoms from North American and European lakesGLOBAL CHANGE BIOLOGY, Issue 11 2008KATHLEEN RÜHLAND Abstract A synthesis of over 200 diatom-based paleolimnological records from nonacidified/nonenriched lakes reveals remarkably similar taxon-specific shifts across the Northern Hemisphere since the 19th century. Our data indicate that these diatom shifts occurred in conjunction with changes in freshwater habitat structure and quality, which, in turn, we link to hemispheric warming trends. Significant increases in the relative abundances of planktonic Cyclotella taxa (P<0.01) were concurrent with sharp declines in both heavily silicified Aulacoseira taxa (P<0.01) and benthic Fragilaria taxa (P<0.01). We demonstrate that this trend is not limited to Arctic and alpine environments, but that lakes at temperate latitudes are now showing similar ecological changes. As expected, the onset of biological responses to warming occurred significantly earlier (P<0.05) in climatically sensitive Arctic regions (median age=ad 1870) compared with temperate regions (median age=ad 1970). In a detailed paleolimnological case study, we report strong relationships (P<0.005) between sedimentary diatom data from Whitefish Bay, Lake of the Woods (Ontario, Canada), and long-term changes in air temperature and ice-out records. Other potential environmental factors, such as atmospheric nitrogen deposition, could not explain our observations. These data provide clear evidence that unparalleled warming over the last few decades resulted in substantial increases in the length of the ice-free period that, similar to 19th century changes in high-latitude lakes, likely triggered a reorganization of diatom community composition. We show that many nonacidified, nutrient-poor, freshwater ecosystems throughout the Northern Hemisphere have crossed important climatically induced ecological thresholds. These findings are worrisome, as the ecological changes that we report at both mid- and high-latitude sites have occurred with increases in mean annual air temperature that are less than half of what is projected for these regions over the next half century. [source] Is the Sonoran Desert losing its cool?GLOBAL CHANGE BIOLOGY, Issue 12 2005Jeremy L. Weiss Abstract Freezing temperatures strongly influence vegetation in the hottest desert of North America, in part determining both its overall boundary and distributions of plant species within. To evaluate recent variability of freezing temperatures in this context, minimum temperature data from weather stations in the Sonoran Desert are examined. Data show widespread warming trends in winter and spring, decreased frequency of freezing temperatures, lengthening of the freeze-free season, and increased minimum temperatures per winter year. Local land use and multidecadal modes of the global climate system such as the Pacific decadal oscillation and the Atlantic multidecadal oscillation do not appear to be principal drivers of this warming. Minimum temperature variability in the Sonoran Desert does, however, correspond to global temperature variability attributed to human-dominated global warming. With warming expected to continue at faster rates throughout the 21st century, potential ecological responses may include contraction of the overall boundary of the Sonoran Desert in the south-east and expansion northward, eastward, and upward in elevation, as well as changes to distributions of plant species within and other characteristics of Sonoran Desert ecosystems. Potential trajectories of vegetation change in the Sonoran Desert region may be affected or made more difficult to predict by uncertain changes in warm season precipitation variability and fire. Opportunities now exist to investigate ecosystem response to regional climate disturbance, as well as to anticipate and plan for continued warming in the Sonoran Desert region. [source] Implications of global climate change for snowmelt hydrology in the twenty-first centuryHYDROLOGICAL PROCESSES, Issue 7 2009Jennifer C. Adam Abstract For most of the global land area poleward of about 40° latitude, snow plays an important role in the water cycle. The (seasonal) timing of runoff in these areas is especially sensitive to projected losses of snowpack associated with warming trends, whereas projected (annual) runoff volume changes are primarily associated with precipitation changes, and to a lesser extent, with changes in evapotranspiration (ET). Regional studies in the USA (and especially the western USA) suggest that hydrologic adjustments to a warming climate have been ongoing since the mid-twentieth century. We extend the insights extracted from the western USA to the global scale using a physically based hydrologic model to assess the effects of systematic changes in precipitation and temperature on snow-affected portions of the global land area as projected by a suite of global climate models. While annual (and in some cases seasonal) changes in precipitation are a key driver of projected changes in annual runoff, we find, as in the western USA, that projected warming produces strong decreases in winter snow accumulation and spring snowmelt over much of the affected area regardless of precipitation change. Decreased snowpack produces decreases in warm-season runoff in many mid- to high-latitude areas where precipitation changes are either moderately positive or negative in the future projections. Exceptions, however, occur in some high-latitude areas, particular in Eurasia, where changes in projected precipitation are large enough to result in increased, rather than decreased, snow accumulation. Overall, projected changes in snowpack and the timing of snowmelt-derived runoff are largest near the boundaries of the areas that currently experience substantial snowfall, and at least qualitatively, they mirror the character of observed changes in the western USA. Copyright © 2008 John Wiley & Sons, Ltd. [source] Antarctic climate change during the last 50 yearsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2005John Turner Abstract An erratum has been published for this article in International Journal of Climatology 25 (8) 2005, 1147,1148. The Reference Antarctic Data for Environmental Research (READER) project data set of monthly mean Antarctic near-surface temperature, mean sea-level pressure (MSLP) and wind speed has been used to investigate trends in these quantities over the last 50 years for 19 stations with long records. Eleven of these had warming trends and seven had cooling trends in their annual data (one station had too little data to allow an annual trend to be computed), indicating the spatial complexity of change that has occurred across the Antarctic in recent decades. The Antarctic Peninsula has experienced a major warming over the last 50 years, with temperatures at Faraday/Vernadsky station having increased at a rate of 0.56 °C decade,1 over the year and 1.09 °C decade,1 during the winter; both figures are statistically significant at less than the 5% level. Overlapping 30 year trends of annual mean temperatures indicate that, at all but two of the 10 coastal stations for which trends could be computed back to 1961, the warming trend was greater (or the cooling trend less) during the 1961,90 period compared with 1971,2000. All the continental stations for which MSLP data were available show negative trends in the annual mean pressures over the full length of their records, which we attribute to the trend in recent decades towards the Southern Hemisphere annular mode (SAM) being in its high-index state. Except for Halley, where the trends are constant, the MSLP trends for all stations on the Antarctic continent for 1971,2000 were more negative than for 1961,90. All but two of the coastal stations have recorded increasing mean wind speeds over recent decades, which is also consistent with the change in the nature of the SAM. Copyright © 2005 Royal Meteorological Society [source] An analysis of Icelandic climate since the nineteenth centuryINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2004Edward Hanna Abstract New, long monthly series of Icelandic air pressure, temperature, precipitation and sunshine data are presented and analysed to determine possible evidence of recent climatic changes in Iceland. Climatic series are compared with the North Atlantic oscillation (NAO) indices; Icelandic temperature and precipitation are moderately but significantly correlated with the NAO. An updated south,north Iceland temperature index is discussed in relation to 20th century reductions in sea-ice coverage. Net warming over Iceland occurred over all long-term records from the mid19th century to the present, consistent with observed global warming trends, but superimposed on this was a marked cooling between the 1940s and early 1980s; Icelandic warming resumed around 1985. The mid,late 20th century cooling is in agreement with observed cooling in southern Greenland, suggesting that large-scale changes in atmospheric circulation were probably responsible. The 1930s was the warmest decade of the 20th century in Iceland, in contrast to the Northern Hemisphere land average. There was a distinct 20th century dipole in temperatures between Iceland and northwestern Europe, with 1941 serving as an extreme year, i.e. cold Europe and warm Iceland and Greenland. There are also signs of a precipitation increase since the late 19th century, although this is significant for only one out of three stations. Moreover, precipitation rates exhibit a positive correlation with temperature. There were no statistically significant overall long-term changes in pressure or sunshine duration. However, there are statistically significant negative correlations of precipitation with the sunshine data. There is evidence of possible solar forcing of Icelandic temperature and pressure. Results from the analysis aid our understanding of recent and ongoing changes in Icelandic and North Atlantic climate. The results should help us interpret these changes in the context of larger scale atmospheric/subpolar variability and future climate-change predictions. Copyright © 2004 Royal Meteorological Society [source] | |||||||||||||||||||||||||