Dansgaard-Oeschger events: tipping points in the climate system

Dansgaard-Oeschger events are a prominent mode of variability in the records of the last glacial cycle. Various prototype models have been proposed to explain these rapid climate fluctuations, and no agreement has emerged on which may be the more correct for describing the paleoclimatic signal. In this work, we assess the bimodality of the system reconstructing the topology of the multi--dimensional attractor over which the climate system evolves. We use high-resolution ice core isotope data to investigate the statistical properties of the climate fluctuations in the period before the onset of the abrupt change. We show that Dansgaard-Oeschger events have weak early warning signals if the ensemble of events is considered. We find that the statistics are consistent with the switches between two different climate equilibrium states in response to a changing external forcing (e.g. solar, ice sheets...), either forcing directly the transition or pacing it through stochastic resonance. These findings are most consistent with a model that associates Dansgaard-Oeschger with changing boundary conditions, and with the presence of a bifurcation point.Comment: Final typeset version freely available at: Clim. Past, 9, 323-333, 2013 www.clim-past.net/9/323/2013/ doi:10.5194/cp-9-323-201

Helden of Verraders Fractieafsplitsingen in de 20ste en 21ste eeuw - De reacties en haar betrokkenen

A partir da constatação empírica da proximidade entre duas representações urbanas – a pintura da Rua Nova dos Mercadores, de Lisboa, pertencente à Kelmscott Manor Collection (c. 1570) e a arquitetura de fundo do Martírio de S. Sebastião, pintado por Gregório Lopes para a Charola do Convento de Cristo em Tomar (década de 1530) – e das conclusões que daí decorrem, revisitam-se algumas das mais emblemáticas representações iconográficas da cidade, as teses que suportam a sua identificação e a importância de que se revestem para o conhecimento dos espaços centrais da Lisboa quinhentista e, assim, da sua imagem, tão descrita quanto ainda deficientemente imaginada.From the empirical recognition of the connection between two urban representations – the depiction of the Rua Nova dos Mercadores (New Street of Merchants), in Lisbon, belonging to the Kelmscott Manor Collection (c. 1570) and the background architecture of the Martyrdom of St. Sebastian, painted by Gregório Lopes for the Convent of Christ in Tomar (1530s) – and its subsequent conclusions, this paper revisits some of the most iconic iconographic representations of the city, the arguments that supports their identification and their importance for the knowledge of the central areas of the 16th century Lisbon, city so often described and yet so poorly imagined

Historical overview of (non-opioid) reversal agents of opioid-induced respiratory depression (OIRD): Lessons from the past and new developments

The development of respiratory stimulants and opioid antagonists to treat opioid induced respiratory depression remains one of the biggest challenges in respiratory research. A variety of substances with stimulatory effects on respiration have been shown to be of little use in clinical practice, either because of narrow margins of safety or due to serious side effects. With the introduction of naloxone a safe treatment for OIRD came within reach, although it reverses all opioid effects, thereby also affecting analgesia. This makes naloxone a very useful drug to treat life-threatening OIRD, but not efficacious for prevention of OIRD. Recent studies have shown that the development of ampakines and potassium-channel blockers such as GAL021 make prevention of OIRD without incidence of serious side effects possible. In the forthcoming years these respiratory stimulants might become a valuable addition to the anesthesiologists’ armamentarium. The development of respiratory stimulants and opioid antagonists to treat opioid induced respiratory depression remains one of the biggest challenges in respiratory research. A variety of substances with stimulatory effects on respiration have been shown to be of little use in clinical practice, either because of narrow margins of safety or due to serious side effects. With the introduction of naloxone a safe treatment for OIRD came within reach, although it reverses all opioid effects, thereby also affecting analgesia. This makes naloxone a very useful drug to treat life-threatening OIRD, but not efficacious for prevention of OIRD. Recent studies have shown that the development of ampakines and potassium-channel blockers such as GAL021 make prevention of OIRD without incidence of serious side effects possible. In the forthcoming years these respiratory stimulants might become a valuable addition to the anesthesiologists’ armamentarium.Perioperative Medicine: Efficacy, Safety and Outcom

Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium

Climate proxy data provide noisy, and spatially incomplete information on some aspects of past climate states, whereas palaeosimulations with climate models provide global, multi-variable states, which may however differ from the true states due to unpredictable internal variability not related to climate forcings, as well as due to model deficiencies. Using data assimilation for combining the empirical information from proxy data with the physical understanding of the climate system represented by the equations in a climate model is in principle a promising way to obtain better estimates for the climate of the past. <br><br> Data assimilation has been used for a long time in weather forecasting and atmospheric analyses to control the states in atmospheric General Circulation Models such that they are in agreement with observation from surface, upper air, and satellite measurements. Here we discuss the similarities and the differences between the data assimilation problem in palaeoclimatology and in weather forecasting, and present and conceptually compare three data assimilation methods that have been developed in recent years for applications in palaeoclimatology. All three methods (selection of ensemble members, Forcing Singular Vectors, and Pattern Nudging) are illustrated by examples that are related to climate variability over the extratropical Northern Hemisphere during the last millennium. In particular it is shown that all three methods suggest that the cold period over Scandinavia during 1790–1820 is linked to anomalous northerly or easterly atmospheric flow, which in turn is related to a pressure anomaly that resembles a negative state of the Northern Annular Mode

Impact of climate model resolution on soil moisture projections in central-western Europe

Global climate models project widespread decreases in soil moisture over large parts of Europe. This paper investigates the impact of model resolution on the magnitude and seasonality of future soil drying in central-western Europe. We use the general circulation model EC-Earth to study two 30-year periods representative of the start and end of the 21st century under low-to-moderate greenhouse gas forcing (RCP4.5). In our study area, central-western Europe, at high spatial resolution (∼25&thinsp;km) soil drying is more severe and starts earlier in the season than at standard resolution (∼112&thinsp;km). Here, changes in the large-scale atmospheric circulation and local soil moisture feedbacks lead to enhanced evapotranspiration in spring and reduced precipitation in summer. A more realistic position of the storm track at high model resolution leads to reduced biases in precipitation and temperature in the present-day climatology, which act to amplify future changes in evapotranspiration in spring. Furthermore, in the high-resolution model a stronger anticyclonic anomaly over the British Isles extends over central-western Europe and supports soil drying. The resulting drier future land induces stronger soil moisture feedbacks that amplify drying conditions in summer. In addition, soil-moisture-limited evapotranspiration in summer promotes sensible heating of the boundary layer, which leads to a lower relative humidity with less cloudy conditions, an increase in dry summer days, and more incoming solar radiation. As a result a series of consecutive hot and dry summers appears in the future high-resolution climate. The enhanced drying at high spatial resolution suggests that future projections of central-western European soil drying by CMIP5 models have been potentially underestimated. Whether these results are robust has to be tested with other global climate models with similar high spatial resolutions.</p