895 resultados para Climate Change: Learning from the past climate


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Aerosols are known to have important effects on climate, the atmosphere, and human health. The extent of those effects is unknown and largely depend on the interaction of aerosols with water in the atmosphere. Ambient aerosols are complex mixtures of both inorganic and organic compounds. The cloud condensation nuclei (CCN) activities, hygroscopic behavior and particle morphology of a monocarboxylic amino acid (leucine) and a dicarboxylic amino acid (glutamic acid) were investigated. Activation diameters at various supersaturation conditions were experimentally determined and compared with Köhler theoretical values. The theory accounts for both surface tension and the limited solubility of organic compounds. It was discovered that glutamic acid aerosols readily took on water both when relative humidity was less than 100% and when the supersaturation condition was reached, while leucine did not show any water activation at those conditions. Moreover, the study also suggests that Köhler theory describes CCN activity of organic compounds well when only surface tension of the compound is taken into account and complete solubility is assumed. Single parameter ¿ was also computed using both CCN data and hygroscopic growth factor (GF). The results of ¿ range from 0.17 to 0.53 using CCN data and 0.09 to 0.2 using GFs. Finally, the study suggests that during the water-evaporation/particle-nucleation process, crystallization from solution droplets takes place at different locations: for glutamic acid at the particles¿ center and leucine at the particles¿ boundary.

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Recent advances in the field of statistical learning have established that learners are able to track regularities of multimodal stimuli, yet it is unknown whether the statistical computations are performed on integrated representations or on separate, unimodal representations. In the present study, we investigated the ability of adults to integrate audio and visual input during statistical learning. We presented learners with a speech stream synchronized with a video of a speaker's face. In the critical condition, the visual (e.g., /gi/) and auditory (e.g., /mi/) signals were occasionally incongruent, which we predicted would produce the McGurk illusion, resulting in the perception of an audiovisual syllable (e.g., /ni/). In this way, we used the McGurk illusion to manipulate the underlying statistical structure of the speech streams, such that perception of these illusory syllables facilitated participants' ability to segment the speech stream. Our results therefore demonstrate that participants can integrate audio and visual input to perceive the McGurk illusion during statistical learning. We interpret our findings as support for modality-interactive accounts of statistical learning.

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The conference on Global Change and the World’s Mountains held in Perth, Scotland, in 2010 offered a unique opportunity to analyze the state and progress of mountain research and its contribution to sustainable mountain development, as well as to reflect on required reorientations of research agendas. In this paper we provide the results of a three-step assessment of the research presented by 450 researchers from around the world. First, we determined the state of the art of mountain research and categorized it based on the analytical structure of the Global Land Project (GLP 2005). Second, we identified emerging themes for future research. Finally, we assessed the contribution of mountain research to sustainable development along the lines of the Grand Challenges in Global Sustainability Research (International Council for Science 2010). Analysis revealed that despite the growing recognition of the importance of more integrative research (inter- and transdisciplinary), the research community gathered in Perth still focuses on environmental drivers of change and on interactions within ecological systems. Only a small percentage of current research seeks to enhance understanding of social systems and of interactions between social and ecological systems. From the ecological systems perspective, a greater effort is needed to disentangle and assess different drivers of change and to investigate impacts on the rendering of ecosystem services. From the social systems perspective, significant shortcomings remain in understanding the characteristics, trends, and impacts of human movements to, within, and out of mountain areas as a form of global change. Likewise, sociocultural drivers affecting collective behavior as well as incentive systems devised by policy and decision makers are little understood and require more in-depth investigation. Both the complexity of coupled social– ecological systems and incomplete data sets hinder integrated systems research. Increased understanding of linkages and feedbacks between social and ecological systems will help to identify nonlinearities and thresholds (tipping points) in both system types. This presupposes effective collaboration between ecological and social sciences. Reflections on the Grand Challenges in Sustainability Research put forth by the International Council for Science (2010) reveal the need to intensify research on effective responses and innovations. This will help to achieve sustainable development in mountain regions while maintaining the core competence of mountain research in forecasting and observation.

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The thermometer-based global surface temperature time series (GST) commands a prominent role in the evidence for global warming, yet this record has considerable uncertainty. An independent record with better geographic coverage would be valuable in understanding recent change in the context of natural variability. We compiled the Paleo Index (PI) from 173 temperature-sensitive proxy time series (corals, ice cores, speleothems, lake and ocean sediments, historical documents). Each series was normalized to produce index values of change relative to a 1901–2000 base period; the index values were then averaged. From 1880 to 1995, the index trends significantly upward, similar to the GST. Smaller-scale aspects of the GST including two warming trends and a warm interval during the 1940s are also observed in the PI. The PI extends to 1730 with 67 records. The upward trend appears to begin in the early 19th century but the year-to-year variability is large and the 1730–1929 trend is small.

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Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.

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One of the action items arising from the work of the Campus Climate Implementation Team and the President’s Advisory Committee on Diversity was a request from the President to the Provost to review the Dialogues on Diversity course. The Provost instructed this Task Force to review the current Dialogues on Diversity course to determine how it should be continued for optimal impact and to determine whether it is appropriate to add a “Dialogues—Part 2” to the curriculum. The Provost’s charge to the Task Force also asked for recommendations that include details on the following components of the current program: goals and objectives of the revised course administration and recommended department home for the revised course possibility of and need for a second course optimal coordination with other programs/initiatives on campus.

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Objective: Firearms are the most common method of suicide among young men in Switzerland. From March 2003 through February 2004, the number of Swiss soldiers was halved as a result of an army reform (Army XXI), leading to a decrease in the availability of guns nationwide. The authors investigated the patterns of the overall suicide rate and the firearm suicide rate before and after the reform. Method: Using a naturalistic study design, the authors compared suicide rates before (1995–2003) and after the intervention (2004–2008) in the affected population (men ages 18–43) and in two comparison groups (women ages 18–44 and men ages 44–53). Data were received from the Swiss Federal Statistical Office. Interrupted time series analysis was used to control for preexisting temporal trends. Alternative methods (Poisson regression, autocorrelation analysis, and surrogate data tests) were used to check validity. Results: The authors found a reduction in both the overall suicide rate and the firearm suicide rate after the Army XXI reform. No significant increases were found for other suicide methods overall. An increase in railway suicides was observed. It was estimated that 22% of the reduction in firearm suicides was substituted by other suicide methods. The attenuation of the suicide rate was not compensated for during the follow-up years. Neither of the comparison groups showed statistically significant changes in firearm suicide rate and overall suicide rate. Conclusions: The restriction of firearm availability in Switzerland resulting from the Army XXI reform was followed by an enduring decrease in the general suicide rate.