Rétroaction climatique | EPFL Graph Search

Une rétroaction climatique est le phénomène par lequel un effet sur le climat agit en retour sur ses causes d'une manière qui peut le stabiliser ou au contraire l'amplifier. Dans le premier cas on parle de rétroaction négative (s'opposant à l'effet) dans le second, de rétroaction positive (renforçant l'effet), ce qui peut conduire à un emballement. Ce phénomène est important pour comprendre le réchauffement climatique car ces rétroactions peuvent amplifier ou atténuer l'effet de chaque forçage climatique et jouent donc un rôle important dans la détermination de la sensibilité climatique et les projections sur le climat futur. Le terme « forçage » signifie un changement qui peut « pousser » le système climatique dans le sens du réchauffement ou du refroidissement. Un exemple de forçage climatique est l'augmentation des concentrations de gaz à effet de serre dans l'atmosphère. Par définition, les forçages sont externes au système climatique tandis que leurs rétroactions sont internes ; en essence, les rétroactions représentent les processus internes au système. Certaines rétroactions peuvent agir de manière relativement isolée par rapport au reste du système climatique ; d'autres au contraire peuvent être étroitement couplées ; de ce fait, il n'est pas toujours évident de déterminer à quel point un processus particulier agit sur le système. Les forçages et les rétroactions déterminent ensemble l'ampleur et la rapidité des changements climatiques. La principale rétroaction positive du réchauffement climatique est la tendance du réchauffement à augmenter la quantité de vapeur d'eau présente dans l'atmosphère, ce qui conduit à un accroissement de l'effet de serre et donc à un réchauffement plus important. La principale réaction négative provient de la loi de Stefan-Boltzmann : la quantité de chaleur émise par la Terre dans l'espace évolue avec la puissance quatre de la température de la surface et de l'atmosphère de la Terre. Les observations et les modélisations montrent que le bilan net des rétroactions du réchauffement est positif.

Toward Assessing the Sensitivity of Buildings to Changes in Climate

Sönke Frederik Horn

A building is designed for one set of typical climatic conditions. In the context of expected climate change, substantial numbers of existing and new buildings are expected to survive long enough to experience perceptible shifts in climate ‘normals’ (averages). This is problematic for predicting building performance, largely because the exact nature of climate change is hard to predict with certainty. Thus an optimal design is not only tuned to the original design conditions, but is also robust to changes in climatic conditions in the sense of a low sensitivity of its performance. To predict a building’s response to changes in typical weather, two inputs are required: weather data representing this change, and suitable metrics to compare building performance across different climate normals. This report presents initial work on a proposed method for assessing the sensitivity of new or existing buildings to climate change. This method begins with a selection of weather files to represent climate change, then quantifies a building’s passive performance in those climates using an enthalpy-based metric, and ends with a graphical analysis of the performance of the building in different climates to assess its robustness. In this report, we propose an objective performance metric based on the extent to which a building creates indoor conditions passively, i.e. without auxiliary systems. Initial work suggests that the performance assessment carried out here is reproducible and applicable for indoor environment design and evaluation in different ranges of climate change. This approach enables a comparison of building performance without the bias introduced by inherent differences in climatic conditions.

2013

Evaluation and extension of an automated system to diagnose the health of premature babies

Camille Joggi

Premature babies are not fully equipped to deal with the outside world. Their immature bodies make them highly at risk to a large number of physiological complications. Therefore, while they are still immature, premature babies are taken care of in neonatology intensive care units, where they are kept in a controlled and protective environment. In these units, the babies' vital parameters, such as their heart rate and temperature, are tightly monitored. The devices used to record this data are fitted with alarms that are triggered automatically when something wrong is detected. However, the alarm systems currently used are often unable to discriminate between real physiological problems and artefacts that should be ignored (e.g. when a measurement device drops-out). As a result, these systems produce a high rate of false alarms, where the alarm is triggered when nothing is clinically wrong. The can have unwanted consequences: first, it creates a noisy environment, which may disturb the babies; second, it can lead to the alarm being ignored when there is actually something wrong. In order to address this problem, my host laboratory has constructed a system that can automatically infer the state of health of premature babies in neonatology units, based on their recorded physiological data. The new system is designed to be able to deal with artefactual changes in the measurements, hopefully resulting in a reduced number of false alarms. In this thesis, I describe my contribution to this project, which is twofold. The first part deals with the problem of evaluating the performance of the system. To do this, I developed an online feedback process, where clinicians could provide information about the true clinical interpretation of the physiological data, which could be compared to the output of the system. The feedbacks provided by the clinicians were then analysed to investigate how the system could be improved. The second part of my thesis was motivated be early feedbacks from the clinicians, which indicated that the system was unable to deal with changes in the humidity measurements that occurred when the incubator door was opened and closed. To address this, I extended the current system, so that it was able to account for these changes, thereby increasing its capability to detect "true" physiological problems during the period after the incubator door is closed.

2011

Evaluation and extension of an automated system to diagnose the health of premature babies

Camille Joggi

2011