32 research outputs found
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 donnĂ©es de haute prĂ©cision de chronomĂ©trage des pulsars rapides vont contribuer significativement Ă l'astrophysique des Ă©toiles Ă neutrons, Ă la dynamique du systĂšme solaire, Ă l'astromĂ©trie, Ă la mĂ©trologie du temps et Ă la cosmologie. Deux annĂ©es de donnĂ©es de chronomĂ©trage du pulsar rapide PSR1937+214 ont Ă©tĂ© analysĂ©es afin de dĂ©terminer d'Ă©ventuelles erreurs systĂ©matiques introduites par les modĂšles d'analyse. Un logiciel d'analyse a Ă©tĂ© dĂ©veloppĂ© Ă cette fin. Des erreurs systĂ©matiques bien supĂ©rieures aux incertitudes thĂ©oriques calculĂ©es ont ainsi Ă©tĂ© rĂ©vĂ©lĂ©es. Les paramĂštres du pulsar dĂ©terminĂ©s par la procĂ©dure d'analyse, comme sa pĂ©riode et sa position, dĂ©pendent alors fortement des thĂ©ories du mouvement de la Terre et des Ă©chelles de temps utilisĂ©es dans l'analyse. Dâautre part, des observations de chronomĂ©trage de pulsars rapides ont dĂ©butĂ© Ă l'Observatoire de Nançay. Celles-ci nĂ©cessitent un dispositif spĂ©cial afin de compenser l'effet de dispersion de la matiĂšre ionisĂ©e interstellaire. Le dispositif adopte et construit Ă Nançay Ă cet effet est dĂ©crit ainsi que les programmes permettant son fonctionnement. Les mĂ©thodes d'observation et les rĂ©sultats prĂ©liminaires d'une campagne d'observation effectuĂ©e au cours de l'Ă©tĂ© 1988 sont donnĂ©s
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 modelâs 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 COâą, we show that there is a positive feedback between the climate system and the carbon cycle. Climate change reduces land and ocean uptake of COâą, respectively by 54% and 35% at 4 x COâą. This negative impact implies that for prescribed anthropogenic COy. emissions, the atmospheric COâą 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 COâą. 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