Contrasts in the effects on climate of anthropogenic sulfate aerosols between the 20th and the 21st century: Contrasts in the effects on climate of anthropogenic sulfate aerosolsbetween the 20th and the 21st century

In this study, we examine the time evolution of the relative contribution of sulfate aerosols and greenhouse gases to anthropogenic climate change. We use the new IPSL-CM4 coupled climate model for which the first indirect effect of sulfate aerosols has been calibrated using POLDER satellite data. For the recent historical period the sulfate aerosols play a key role on the temperature increase with a cooling effect of 0.5 K, to be compared to the 1.4 K warming due to greenhouse gas increase. In contrast, the projected temperature change for the 21st century is remarkably independent of the effects of anthropogenic sulfate aerosols for the SRES-A2 scenario. Those results are interpreted comparing the different radiative forcings, and can be extended to other scenarios. We also highlight that the first indirect effect of aerosol strongly depends on the land surface model by changing the cloud cover

Contrasts in the effects on climate of anthropogenic sulfate aerosols between the 20th and the 21st century: Contrasts in the effects on climate of anthropogenic sulfate aerosolsbetween the 20th and the 21st century

In this study, we examine the time evolution of the relative contribution of sulfate aerosols and greenhouse gases to anthropogenic climate change. We use the new IPSL-CM4 coupled climate model for which the first indirect effect of sulfate aerosols has been calibrated using POLDER satellite data. For the recent historical period the sulfate aerosols play a key role on the temperature increase with a cooling effect of 0.5 K, to be compared to the 1.4 K warming due to greenhouse gas increase. In contrast, the projected temperature change for the 21st century is remarkably independent of the effects of anthropogenic sulfate aerosols for the SRES-A2 scenario. Those results are interpreted comparing the different radiative forcings, and can be extended to other scenarios. We also highlight that the first indirect effect of aerosol strongly depends on the land surface model by changing the cloud cover

Chronométrage du pulsar milliseconde PSR1937+214 : analyse Astrométrique et Observations à Nançay

not availableLes données de haute précision de chronométrage des pulsars rapides vont contribuer significativement à l'astrophysique des étoiles à neutrons, à la dynamique du système solaire, à l'astrométrie, à la métrologie du temps et à la cosmologie. Deux années de données de chronométrage du pulsar rapide PSR1937+214 ont été analysées afin de déterminer d'éventuelles erreurs systématiques introduites par les modèles d'analyse. Un logiciel d'analyse a été développé à cette fin. Des erreurs systématiques bien supérieures aux incertitudes théoriques calculées ont ainsi été révélées. Les paramètres du pulsar déterminés par la procédure d'analyse, comme sa période et sa position, dépendent alors fortement des théories du mouvement de la Terre et des échelles de temps utilisées dans l'analyse. D’autre part, des observations de chronométrage de pulsars rapides ont débuté à l'Observatoire de Nançay. Celles-ci nécessitent un dispositif spécial afin de compenser l'effet de dispersion de la matière ionisée interstellaire. Le dispositif adopte et construit à Nançay à cet effet est décrit ainsi que les programmes permettant son fonctionnement. Les méthodes d'observation et les résultats préliminaires d'une campagne d'observation effectuée au cours de l'été 1988 sont donnés

The stratospheric version of LMDz: dynamical climatologies, arctic oscillation, and impact on the surface climate

International audienceA climatology of the stratosphere is determined from a 20-year integration with the stratospheric version of the Atmospheric General Circulation Model LMDz. The model has an upper boundary at near 65 km, uses a Doppler spread non-orographic gravity waves drag parameterization and a subgrid-scale orography parameterization. It also has a Rayleigh damping layer for resolved waves only (not the zonal mean flow) over the top 5 km. This paper describes the basic features of the model and some aspects of its radiative-dynamical climatology. Standard first order diagnostics are presented but some emphasis is given to the model’s ability to reproduce the low frequency variability of the stratosphere in the winter northern hemisphere. In this model, the stratospheric variability is dominated at each altitudes by patterns which have some similarities with the arctic oscillation (AO). For those patterns, the signal sometimes descends from the stratosphere to the troposphere. In an experiment where the parameterized orographic gravity waves that reach the stratosphere are exaggerated, the model stratosphere in the NH presents much less variability. Although the stratospheric variability is still dominated by patterns that resemble to the AO, the downward influence of the stratosphere along these patterns is near entirely lost. In the same time, the persistence of the surface AO decreases, which is consistent with the picture that this persistence is linked to the descent of the AO signal from the stratosphere to the troposphere. A comparison between the stratospheric version of the model, and its routinely used tropospheric version is also done. It shows that the introduction of the stratosphere in a model that already has a realistic AO persistence can lead to overestimate the actual influence of the stratospheric dynamics onto the surface AO. Although this result is certainly model dependent, it suggests that the introduction of the stratosphere in a GCM also call for a new adjustment of the model parameters that affect the tropospheric variability

Contrasts in the effects on climate of anthropogenic sulfate aerosols between the 20th and the 21st century: Contrasts in the effects on climate of anthropogenic sulfate aerosolsbetween the 20th and the 21st century

In this study, we examine the time evolution of the relative contribution of sulfate aerosols and greenhouse gases to anthropogenic climate change. We use the new IPSL-CM4 coupled climate model for which the first indirect effect of sulfate aerosols has been calibrated using POLDER satellite data. For the recent historical period the sulfate aerosols play a key role on the temperature increase with a cooling effect of 0.5 K, to be compared to the 1.4 K warming due to greenhouse gas increase. In contrast, the projected temperature change for the 21st century is remarkably independent of the effects of anthropogenic sulfate aerosols for the SRES-A2 scenario. Those results are interpreted comparing the different radiative forcings, and can be extended to other scenarios. We also highlight that the first indirect effect of aerosol strongly depends on the land surface model by changing the cloud cover

Positive feedback between future climate change and the carbon cycle

International audienceFuture climate change due to increased atmospheric CO2 may affect land and ocean efficiency to absorb atmospheric CO2. Here, using climate and carbon three-dimensional models forced by a 1% per year increase in atmospheric CO•, we show that there is a positive feedback between the climate system and the carbon cycle. Climate change reduces land and ocean uptake of CO•, respectively by 54% and 35% at 4 x CO•. This negative impact implies that for prescribed anthropogenic COy. emissions, the atmospheric CO• would be higher than the level reached if climate change does not affect the carbon cycle. We estimate the gain of this climate-carbon cycle feedback to be 10% at 2 x CO2 and 20% at 4 x CO•. This translates into a 15% higher mean temperature increase

Contrasts in the effects on climate of anthropogenic sulfate aerosols between the 20th and the 21st century: Contrasts in the effects on climate of anthropogenic sulfate aerosolsbetween the 20th and the 21st century

In this study, we examine the time evolution of the relative contribution of sulfate aerosols and greenhouse gases to anthropogenic climate change. We use the new IPSL-CM4 coupled climate model for which the first indirect effect of sulfate aerosols has been calibrated using POLDER satellite data. For the recent historical period the sulfate aerosols play a key role on the temperature increase with a cooling effect of 0.5 K, to be compared to the 1.4 K warming due to greenhouse gas increase. In contrast, the projected temperature change for the 21st century is remarkably independent of the effects of anthropogenic sulfate aerosols for the SRES-A2 scenario. Those results are interpreted comparing the different radiative forcings, and can be extended to other scenarios. We also highlight that the first indirect effect of aerosol strongly depends on the land surface model by changing the cloud cover