1,721,131 research outputs found
A high-end estimate of sea level rise for practitioners
No full textSea level rise (SLR) is a long-lasting consequence of climate change because global anthropogenic warming takes centuries to millennia to equilibrate for the deep ocean and ice sheets. SLR projections based on climate models support policy analysis, risk assessment and adaptation planning today, despite their large uncertainties. The central range of the SLR distribution is estimated by process-based models. However, risk-averse practitioners often require information about plausible future conditions that lie in the tails of the SLR distribution, which are poorly defined by existing models. Here, a community effort combining scientists and practitioners builds on a framework of discussing physical evidence to quantify high-end global SLR for practitioners. The approach is complementary to the IPCC AR6 report and provides further physically plausible high-end scenarios. High-end estimates for the different SLR components are developed for two climate scenarios at two timescales. For global warming of +2°C in 2100 (RCP2.6/SSP1-2.6) relative to pre-industrial values our high-end global SLR estimates are up to 0.9 m in 2100 and 2.5 m in 2300. Similarly, for a (RCP8.5/SSP5-8.5), we estimate up to 1.6 m in 2100 and up to 10.4 m in 2300. The large and growing differences between the scenarios beyond 2100 emphasize the long-term benefits of mitigation. However, even a modest 2°C warming may cause multi-meter SLR on centennial time scales with profound consequences for coastal areas. Earlier high-end assessments focused on instability mechanisms in Antarctica, while here we emphasize the importance of the timing of ice shelf collapse around Antarctica. This is highly uncertain due to low understanding of the driving processes. Hence both process understanding and emission scenario control high-end SLR
Antarctic ice sheet and oceanographic response to eccentricity forcing during the early Miocene
Get PDFStable isotope records of benthic foraminifera from ODP Site 1264 in the southeastern Atlantic Ocean are presented which resolve the latest Oligocene to early Miocene (~24–19 Ma) climate changes at high temporal resolution (<3 kyr). Using an inverse modelling technique, we decomposed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded episodically during the declining phase of the long-term (~400 kyr) eccentricity cycle and subsequent low short-term (~100 kyr) eccentricity cycle. The largest glaciations are separated by multiple long-term eccentricity cycles, indicating the involvement of a non-linear response mechanism. Our modelling results suggest that during the largest (Mi-1) event, Antarctic ice sheet volume expanded up to its present-day configuration. In addition, we found that distinct ~100 kyr variability occurs during the termination phases of the major Antarctic glaciations, suggesting that climate and ice-sheet response was more susceptible to short-term eccentricity forcing at these times. During two of these termination-phases, ?18O bottom water gradients in the Atlantic ceased to exist, indicating a direct link between global climate, enhanced ice-sheet instability and major oceanographic reorganisations
Carbonaceous particles reveal that Late Holocene dust causes the dark region in the western ablation zone of the Greenland ice sheet
No full textA dark region in the western ablation zone of the Greenland ice sheet is caused by outcropping ice layers that contain more dust than the surrounding brighter ice. These higher amounts of dust were deposited in the accumulation zone of the ice sheet and travelled with the ice to the ablation zone. To deduce the period and the causes of this higher dust deposition, carbonaceous particles in ice samples from the dark region and from brighter reference ice were analysed and used for dating. Samples including ice from directly below the surface contain high amounts of modern organic carbon, probably from microorganisms on the ice surface. Deeper samples reveal low amounts of carbonaceous particles, which are originally deposited in the accumulation zone. The amount of outcropping carbonaceous particles in the dark region seems significantly higher than in the reference ice. One of the samples that contained material initially deposited in the accumulation zone was dated and revealed Late Holocene ages, coinciding with a period of enhanced eolian activity in the nearby tundra. Therefore, variable eolian activity during the Holocene effected dust fluxes towards the ice and hence leads to albedo variations in the present ablation zone of the ice sheet
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Interactions and feedbacks between ice sheets, climate, sea level and the solid Earth
No full textAnthropogenic climate change is one of the largest challenges facing society today. Although mitigating the magnitude of climate change by reducing CO2 emissions is of vital importance, even the most optimistic of future scenarios will still result in significant warming. One of the inevitable consequences of the warming is sea-level rise due to the melting of land ice and the thermal expansion of the. In order to determine an adaptation and mitigation strategy, accurate projections of sea-level rise are required. The vast size of the large ice sheets on Greenland and Antarctica lead to a slow response to a change in climate: it takes years to decades before a change in climate even begins to significantly affect ice sheet growth or retreat, and hundreds to thousands of years to reach a new equilibrium. This implies that observational alone is insufficient to predict future ice-sheet evolution. To overcome this problem, palaeoglaciology, the study of the past behaviour of glaciers and ice sheets, is helpful. In the geological past, Earth’s climate has undergone major changes, some even larger than the ongoing present anthropogenic change, though probably not quite as fast. Often these climate changes, in particular the glacial cycles of the Pleistocene, were accompanied by large changes in ice-sheet size, and therefore sea level. By studying the relation between the climate and the ice sheets in the past, and trying to reproduce their evolution with models, we contribute to the understanding of the Earth system, and the response of ice sheets in the future.
A complication that is implicit in palaeoglaciology more than in future projections, is that the interaction between ice sheets and climate works in two directions. Changes in temperature and precipitation patterns will affect how much snow accumulates and melts on an ice sheet. However, changes in ice extent and geometry also affect local temperatures through changes in surface albedo and altitude, and in addition affect precipitation through orographic forcing and changes in large-scale atmospheric circulation. Changes in ocean temperatures affect the melting of floating ice, but the addition of large amounts of fresh melt water to the ocean can affect ocean currents.
As a consequence, a change in any part of the Earth system will directly or indirectly affect all the other parts. Throughout Earth’s geological past, all the different components changed in concert, continuously affecting each other through coupling effects and the associated feedback processes. Any model that aims to successfully simulate the behaviour of one or more components will therefore need to include an accurate representation of the interactions and feedback processes in the Earth system.
This thesis aims to incorporate several of these feedback processes into an existing ice- sheet model, and use that model configuration to reproduce the behaviour of ice-sheets during different episodes during the past several million years
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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