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Arctic precipitation in the form of rain is forecast to become more prevalent in a warmer world but with seasonal and interannual changes modulated by natural modes of variability. Experiencing rapid hydroclimatic changes in the Arctic, Svalbard serves as an ideal study location due to its exposure to oceanic and atmospheric variability in the North Atlantic region. Here we use climate data from paleoproxies, observations, and a climate model to demonstrate that wet and warm extremes in Svalbard over the last two millennia are linked to the presence of atmospheric blocking regimes over Scandinavia and the Ural mountain region. Rainfall episodes lead to the deposition of coarse sediment particles and high levels of calcium in Linnévatnet, a lake in southwest Svalbard, with the coarsest sediments consistently deposited during atmospheric blocking events. A unique annually resolved sediment record from Linnévatnet confirms that this linkage has been persistent over the past 2000 years. Our record also shows that a millennial-scale decline in Svalbard precipitation ended around the middle of the 19th century, followed by several unprecedented extreme events in recent years. As warming continues and sea ice recedes, future Svalbard floods will become more intense during episodes of Scandinavian and Ural blocking.
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In Arabia, the first half of the sixth century CE was marked by the demise of Himyar, the dominant power in Arabia until 525 CE. Important social and political changes followed, which promoted the disintegration of the major Arabian polities. Here, we present hydroclimate records from around Southern Arabia, including a new high-resolution stalagmite record from northern Oman. These records clearly indicate unprecedented droughts during the sixth century CE, with the most severe aridity persisting between ~500 and 530 CE. We suggest that such droughts undermined the resilience of Himyar and thereby contributed to the societal changes from which Islam emerged.
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Sequías , Islamismo , Cambio Social , Arabia , Sequías/historia , Historia Medieval , Islamismo/historia , Omán , Cambio Social/historiaRESUMEN
Declining temperature has been thought to explain the abandonment of Norse settlements, southern Greenland, in the early 15th century, although limited paleoclimate evidence is available from the inner settlement region itself. Here, we reconstruct the temperature and hydroclimate history from lake sediments at a site adjacent to a former Norse farm. We find no substantial temperature changes during the settlement period but rather that the region experienced a persistent drying trend, which peaked in the 16th century. Drier climate would have notably reduced grass production, which was essential for livestock overwintering, and this drying trend is concurrent with a Norse diet shift. We conclude that increasingly dry conditions played a more important role in undermining the viability of the Eastern Settlement than minor temperature changes.
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The Little Ice Age (LIA) was one of the coldest periods of the postglacial period in the Northern Hemisphere. Although there is increasing evidence that this time interval was associated with weakening of the subpolar gyre (SPG), the sequence of events that led to its weakened state has yet to be explained. Here, we show that the LIA was preceded by an exceptional intrusion of warm Atlantic water into the Nordic Seas in the late 1300s. The intrusion was a consequence of persistent atmospheric blocking over the North Atlantic, linked to unusually high solar activity. The warmer water led to the breakup of sea ice and calving of tidewater glaciers; weakening of the blocking anomaly in the late 1300s allowed the large volume of ice that had accumulated to be exported into the North Atlantic. This led to a weakening of the SPG, setting the stage for the subsequent LIA.
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Global warming due to anthropogenic factors can be amplified or dampened by natural climate oscillations, especially those involving sea surface temperatures (SSTs) in the North Atlantic which vary on a multidecadal scale (Atlantic multidecadal variability, AMV). Because the instrumental record of AMV is short, long-term behavior of AMV is unknown, but climatic teleconnections to regions beyond the North Atlantic offer the prospect of reconstructing AMV from high-resolution records elsewhere. Annually resolved titanium from an annually laminated sedimentary record from Ellesmere Island, Canada, shows that the record is strongly influenced by AMV via atmospheric circulation anomalies. Significant correlations between this High-Arctic proxy and other highly resolved Atlantic SST proxies demonstrate that it shares the multidecadal variability seen in the Atlantic. Our record provides a reconstruction of AMV for the past â¼3 millennia at an unprecedented time resolution, indicating North Atlantic SSTs were coldest from â¼1400-1800 CE, while current SSTs are the warmest in the past â¼2,900 y.
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Calentamiento Global/historia , Temperatura , Regiones Árticas , Océano Atlántico , Atmósfera , Clima , Historia del Siglo XVIII , Historia del Siglo XIX , Historia del Siglo XX , Estaciones del AñoRESUMEN
Wildfire can influence climate directly and indirectly, but little is known about the relationships between wildfire and climate during the Quaternary, especially how wildfire patterns varied over glacial-interglacial cycles. Here, we present a high-resolution soot record from the Chinese Loess Plateau; this is a record of large-scale, high-intensity fires over the past 2.6 My. We observed a unique and distinct glacial-interglacial cyclicity of soot over the entire Quaternary Period synchronous with marine δ18O and dust records, which suggests that ice-volume-modulated aridity controlled wildfire occurrences, soot production, and dust fluxes in central Asia. The high-intensity fires were also found to be anticorrelated with global atmospheric CO2 records over the past eight glacial-interglacial cycles, implying a possible connection between the fires, dust, and climate mediated through the iron cycle. The significance of this hypothetical connection remains to be determined, but the relationships revealed in this study hint at the potential importance of wildfire for the global climate system.
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During the last ice age temperature in the North Atlantic oscillated in cycles known as Dansgaard-Oeschger (D-O) events. The magnitude of Caribbean hydroclimate change associated with D-O variability and particularly with stadial intervals, remains poorly constrained by paleoclimate records. We present a 3.3 thousand-year long stalagmite δ18O record from the Yucatan Peninsula (YP) that spans the interval between 26.5 and 23.2 thousand years before present. We estimate quantitative precipitation variability and the high resolution and dating accuracy of this record allow us to investigate how rainfall in the region responds to D-O events. Quantitative precipitation estimates are based on observed regional amount effect variability, last glacial paleotemperature records, and estimates of the last glacial oxygen isotopic composition of precipitation based on global circulation models (GCMs). The new precipitation record suggests significant low latitude hydrological responses to internal modes of climate variability and supports a role of Caribbean hydroclimate in helping Atlantic Meridional Overturning Circulation recovery during D-O events. Significant in-phase precipitation reduction across the equator in the tropical Americas associated with Heinrich event 2 is suggested by available speleothem oxygen isotope records.
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The differential warming of land and ocean leads to many continental regions in the Northern Hemisphere warming at rates higher than the global mean temperature. Adaptation and conservation efforts will, therefore, benefit from understanding regional consequences of limiting the global mean temperature increase to well below 2°C above pre-industrial levels, a limit agreed upon at the United Nations Climate Summit in Paris in December 2015. Here, we analyze climate model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to determine the timing and magnitude of regional temperature and precipitation changes across the contiguous United States (US) for global warming of 1.5 and 2°C and highlight consensus and uncertainties in model projections and their implications for making decisions. The regional warming rates differ considerably across the contiguous US, but all regions are projected to reach 2°C about 10-20 years before the global mean temperature. Although there is uncertainty in the timing of exactly when the 1.5 and 2°C thresholds will be crossed regionally, over 80% of the models project at least 2°C warming by 2050 for all regions for the high emissions scenario. This threshold-based approach also highlights regional variations in the rate of warming across the US. The fastest warming region in the contiguous US is the Northeast, which is projected to warm by 3°C when global warming reaches 2°C. The signal-to-noise ratio calculations indicate that the regional warming estimates remain outside the envelope of uncertainty throughout the twenty-first century, making them potentially useful to planners. The regional precipitation projections for global warming of 1.5°C and 2°C are uncertain, but the eastern US is projected to experience wetter winters and the Great Plains and the Northwest US are projected to experience drier summers in the future. The impact of different scenarios on regional precipitation projections is negligible throughout the twenty-first century compared to uncertainties associated with internal variability and model diversity.
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Calentamiento Global , Modelos Teóricos , Estaciones del Año , Noroeste de Estados Unidos , Factores de TiempoRESUMEN
We investigated the relationship between distributions of GDGTs, GDGT-based proxies and environmental factors in a stratified lake in northwestern Norway. More than 90% of isoGDGTs were produced at the bottom of the oxycline, indicating a predominance of ammonia-oxidizing Group I.1a of Thaumarchaeota, supported by high crenarchaeol/caldarchaeol ratios. Dissolved oxygen content, rather than temperature, exercised a primary control on TEX86 values. In spite of low BIT value in surface sediment, the reconstructed lake surface temperature was "cold" biased. MBT values in streams and lake surface water were significantly smaller than those in the catchment soil, suggesting in situ production of brGDGTs in streams. A rapid transition of MBT vs. temperature/pH relationships occurring at the bottom of oxycline indicated the differential production of various brGDGTs with D.O. and depths. Only within the oxycline were CBT-based pH values close to in situ pH. Our results confirm earlier studies calling for caution in applying TEX86 as a surface temperature proxy, or MBT and/or CBT for reconstructing pH, in anoxic or euxinic lakes, estuaries and ocean basins. We propose that caldarchaeol/crenarchaeol ratio, an indicator of contributions from methanogenic archaea, together with the BIT and TEX86 proxies, can help reconstruct past levels of stratification.
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Changes of snow occurrence across the central and eastern United States under future warming for the late 21(st) century are investigated by applying an empirical hyperbolic tangent function to both observed and downscaled high spatial resolution (~12.5 km) daily temperature and precipitation, to compare the historical (1981-2000) and future (2081-2100) snow occurrence. The observed distributions of snow frequency show that snow-rain transition zones are mainly zonally distributed, since they are largely determined by temperature, with slight shifts to the south over the Appalachian Mountains. The snow-rain transition zone is located around 38-46°N for November and March, and 32-42°N for winter months (DJF). These observed patterns are reproduced well for the historical period by an ensemble average of multiple general circulation models (GCMs). The probabilistic projections show that the snow-rain transition zone will shift to the north under the background of global warming at magnitudes of 2-6 °C, indicating that large areas will experience a partial, or even a very large, loss of snow occurrence in the future. The northward shifts are about 2° latitude under the representative concentration pathways 4.5 (RCP4.5) scenario and 4° latitude under the RCP8.5 scenario. The percentages of the area losing snow occurrence are also assessed.
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Disentangling the effects of climate change and anthropogenic activities on the environment is a major challenge in paleoenvironmental research. Here, we used fecal sterols and other biogeochemical compounds in lake sediments from northern Norway to identify both natural and anthropogenic signals of environmental change during the late Holocene. The area was first occupied by humans and their grazing animals at â¼2,250 ± 75 calendar years before 1950 AD (calendar years before present). The arrival of humans is indicated by an abrupt increase in coprostanol (and its epimer epicoprostanol) in the sediments and an associated increase in 5ß-stigmastanol (and 5ß-epistigmastanol), which resulted from human and animal feces washing into the lake. Human settlement was accompanied by an abrupt increase in landscape fires (indicated by the rise in pyrolytic polycyclic aromatic hydrocarbons) and a decline in woodland (registered by a change in n-alkane chain lengths from leaf waxes), accelerating a process that began earlier in the Holocene. Human activity and associated landscape changes in the region over the last two millennia were mainly driven by summer temperatures, as indicated by independent tree-ring reconstructions, although there were periods when socioeconomic factors played an equally important role. In this study, fecal sterols in lake sediments have been used to provide a record of human occupancy through time. This approach may be useful in many archeological studies, both to confirm the presence of humans and grazing animals, and to distinguish between anthropogenic and natural factors that have influenced the environment in the past.
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Cambio Climático/historia , Sedimentos Geológicos/análisis , Agricultura/historia , Animales , Arqueología , Ambiente , Heces/química , Historia Antigua , Humanos , Noruega , Esteroles/análisisRESUMEN
High-resolution paleoclimate reconstructions are often restricted by the difficulties of sampling geologic archives in great detail and the analytical costs of processing large numbers of samples. Using sediments from Lake Braya Sø, Greenland, we introduce a new method that provides a quantitative high-resolution paleoclimate record by combining measurements of the alkenone unsaturation index (U37(K)) with non-destructive scanning reflectance spectroscopic measurements in the visible range (VIS-RS). The proxy-to-proxy (PTP) method exploits two distinct calibrations: the in situ calibration of U37(K) to lake water temperature and the calibration of scanning VIS-RS data to down core U37(K) data. Using this approach, we produced a quantitative temperature record that is longer and has 5 times higher sampling resolution than the original U37(K) time series, thereby allowing detection of temperature variability in frequency bands characteristic of the AMO over the past 7,000 years.
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Clima , Sedimentos Geológicos/química , Calibración , GeologíaRESUMEN
This work reports the results of an evaluation study to assess the efficacy of the Early HeartSmarts (EHS) program in schools of the Salt Lake City, Utah, School District. The EHS program is designed to guide teachers with methods that support young children (3-6 y old) in learning emotion self-regulation and key age-appropriate socioemotional competencies with the goal of facilitating their emotional, social, and cognitive development. The study was conducted over one school year using a quasiexperimental longitudinal field research design with 3 measurement points (baseline, preintervention, and postintervention) using The Creative Curriculum Assessment (TCCA), a teacher-scored, 50-item instrument measuring students growth in 4 areas of development: social/emotional, physical, cognitive, and language development. Children in 19 preschool classrooms in the Salt Lake City School District were divided into intervention and control group samples (n = 66 and n = 309, respectively; mean age = 3.6 y). The intervention classes were specifically selected to target children of lower socioeconomic and ethnic minority backgrounds. Overall, there is compelling evidence of the efficacy of the EHS program in increasing total psychosocial development and each of the 4 development areas measured by the TCCA: the results of a series of analyses of covariance found a strong, consistent pattern of large, significant differences on the development measures favoring preschool children who received the EHS program over those in the control group.
Este trabajo informa los resultados de un estudio de evaluación de la eficacia del programa Early Heartsmarts (EHS) en las escuelas del Distrito Escolar de Salt Lake City, Utah. El programa EHS está diseñado para orientar a los maestros respecto de métodos de asistencia a niños pequeños (entre 3 y 6 años de edad) en el aprendizaje de técnicas de autorregulación emocional y competencias socioemocionales fundamentales, adecuadas para su edad, con el fin de favorecer su desarrollo emocional, social y cognitivo. Este estudio se realizó durante un año escolar, conforme un diseño de investigación de campo cuasi experimental y longitudinal, diseñada con tres puntos de medición (punto de partida, intervención previa e intervención posterior), en la que se utilizó una Evaluación del Currículo Creativo (TCCA, por sus siglas en inglés), un instrumento calificado por el maestro de 50 puntos para medir el crecimiento de los estudiantes en 4 áreas del desarrollo: social y emocional, físico, cognitivo y desarrollo del lenguaje. Los niños de los 19 salones de clase de nivel preescolar en el Distrito Escolar de Salt Lake City, se analizaron de manera fraccionada según muestras de intervención y de control de grupo (n=66 y n=309, respectivamente; edad promedio=3 a 6 años). Las clases de intervención fueron seleccionadas específicamente para examinar a niños de bajo nivel socioeconómico y pertenecientes a minorías étnicas. En general, existen pruebas convincentes de la eficacia del programa EHS para fomentar el desarrollo psicosocial total. Respecto de cada una de las 4 áreas de desarrollo que fueron medidas por la TCCA: los resultados de una serie de análisis de la covarianza mostraron un patrón sólido y consistente de diferencias notorias y significativas en las medidas de desarrollo que favorecen a los niños de preescolar que recibieron el programa EHS, respecto de aquellos del grupo de control.
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This study investigated the effects of a novel, classroom-based emotion self-regulation program (TestEdge) on measures of test anxiety, socioemotional function, test performance, and heart rate variability (HRV) in high school students. The program teaches students how to self-generate a specific psychophysiological state--psychophysiological coherence--which has been shown to improve nervous system function, emotional stability, and cognitive performance. Implemented as part of a larger study investigating the population of tenth grade students in two California high schools (N = 980), the research reported here was conducted as a controlled pre- and post-intervention laboratory experiment, using electrophysiological measures, on a random stratified sample of students from the intervention and control schools (N = 136). The Stroop color-word conflict test was used as the experiment's stimulus to simulate the stress of taking a high-stakes test, while continuous HRV recordings were gathered. The post-intervention electrophysiological results showed a pattern of improvement across all HRV measures, indicating that students who received the intervention program had learned how to better manage their emotions and to self-activate the psychophysiological coherence state under stressful conditions. Moreover, students with high test anxiety exhibited increased HRV and heart rhythm coherence even during a resting baseline condition (without conscious use of the program's techniques), suggesting that they had internalized the benefits of the intervention. Consistent with these results, students exhibited reduced test anxiety and reduced negative affect after the intervention. Finally, there is suggestive evidence from a matched-pairs analysis that reduced test anxiety and increased psychophysiological coherence appear to be directly associated with improved test performance--a finding consistent with evidence from the larger study.
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Ansiedad/fisiopatología , Emociones/fisiología , Frecuencia Cardíaca/fisiología , Controles Informales de la Sociedad/métodos , Estrés Psicológico/fisiopatología , Adolescente , Análisis de Varianza , Femenino , Humanos , Masculino , Estudiantes , Encuestas y CuestionariosRESUMEN
Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña-like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation-Arctic Oscillation.
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The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60 degrees N covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.
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Following the suggestions of a recent National Research Council report [NRC (National Research Council) (2006) Surface Temperature Reconstructions for the Last 2,000 Years (Natl Acad Press, Washington, DC).], we reconstruct surface temperature at hemispheric and global scale for much of the last 2,000 years using a greatly expanded set of proxy data for decadal-to-centennial climate changes, recently updated instrumental data, and complementary methods that have been thoroughly tested and validated with model simulation experiments. Our results extend previous conclusions that recent Northern Hemisphere surface temperature increases are likely anomalous in a long-term context. Recent warmth appears anomalous for at least the past 1,300 years whether or not tree-ring data are used. If tree-ring data are used, the conclusion can be extended to at least the past 1,700 years, but with additional strong caveats. The reconstructed amplitude of change over past centuries is greater than hitherto reported, with somewhat greater Medieval warmth in the Northern Hemisphere, albeit still not reaching recent levels.
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Planeta Tierra , Temperatura , Factores de Tiempo , Árboles/fisiologíaAsunto(s)
Clima , Modelos Teóricos , Incertidumbre , National Academy of Sciences, U.S. , Factores de Tiempo , Estados UnidosRESUMEN
OBJECTIVES: This study aims to contribute to a scientific understanding of intuition, a process by which information normally outside the range of conscious awareness is perceived by the body's psychophysiological systems. The first objective, presented in two empirical reports (Part 1 and Part 2), was to replicate and extend the results of previous experiments demonstrating that the body can respond to an emotionally arousing stimulus seconds before it is actually experienced. The second objective, to be presented in a forthcoming publication (Part 3), is to develop a theory that explains how the body receives and processes information involved in intuitive perception. DESIGN: The study used a counterbalanced crossover design, in which 30 calm and 15 emotionally arousing pictures were presented to 26 participants under two experimental conditions: a baseline condition of "normal" psychophysiologic function and a condition of physiological coherence. Primary measures included: skin conductance; the electroencephalogram (EEG), from which cortical event-related potentials (ERP) and heartbeatevoked potentials (HBEP) were derived; and the electrocardiogram (ECG), from which cardiac decelerations/ accelerations were derived. These measures were used to investigate where and when in the brain and body intuitive information is processed. RESULTS: The main findings presented here are: (1) surprisingly, both the heart and brain appear to receive and respond to intuitive information; (2) even more surprisingly, there is compelling evidence that the heart appears to receive intuitive information before the brain; (3) there were significant differences in prestimulus ERPs for calm versus emotional stimuli; (4) the frontal cortex, temporal, occipital, and parietal areas appear to be involved in the processing of prestimulus information; (5) there were significant differences in prestimulus calm/emotional HBEPs, primarily in the coherent mode; (6) there were significant gender differences in the processing of prestimulus information. Especially noteworthy is the apparent interaction between the HBEPs and ERPs in the females, which suggests that the heart modulates the ERP and that females are more attuned to intuitive information from the heart. CONCLUSIONS: Overall, our data suggest that the heart and brain, together, are involved in receiving, processing, and decoding intuitive information. On the basis of these results and those of other research, it would thus appear that intuitive perception is a system-wide process in which both the heart and brain (and possibly other bodily systems) play a critical role. To account for the study's results, Part 3 will develop a theory based on holographic principles explaining how intuitive perception accesses a field of energy into which information about "future" events is spectrally enfolded.