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Nombre de programmes trouvés : 76
Label UNT Conférences

le (54m24s)

Seismic tomography : A giiant inverse problem

In this talk I shall give an overview of the development of seismic tomography: constructing images of elastic properties in the Earth's interior from seismic observations at its surface. The use of ray-theoretical approximations allows us to image long-wavelength structure. To increase resolution, however, we cannot escape using the wave equation. Modeling the waveforms themselves is highly nonlinear, but the nonlinearity of the problem can be kept under control by using secondary observables such as delays of time- and frequency windowed waveforms. The resulting ...
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le (28m0s)

Climate Models: learning from the Past Long-Term Climate Variability

Projections of future climate change rely on global climate models. Such models simulate the dynamics and physics of the coupled atmosphere-ocean system and move towards models of the full Earth system. These models are evaluated on the present day mean climate as well as on climate variability over the last century. Although climate models agree on the overall patterns of future climate change, discrepancies are still displayed between models, both in amplitude and at the regional scale (e.g., IPCC AR5 (2007)). Past climates offer an unique opportunity to evaluate climate models on climate conditions different from the present-day conditions ...
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le (28m58s)

Modelling Forced and Internal Climate Variability During the Last Millennium

At hemispheric scale, the surface temperature is strongly influenced by the 28 variations of the natural (solar and volcanic) and anthropogenic (land-use, sulphate aerosols, greenhouse gas concentrations) forcings. By contrast, at regional scale, the internal variability, which is purely due to the internal dynamics of the climate system, can mask the forced response. As a consequence, before the 20th century, cold or warm periods are rarely global, homogenous phenomena. Furthermore, the response to the forcing could be associated with changes in the frequency of some modes of variability. This interplay between the response of the climate system to the various ...
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le (28m50s)

International Negociations on Climate Change: How to Take Advantage of Risk Aversion to Improve the Conditions for the Emergence of a Consensus

Climate change is one of the best examples of global environmental problems. Countries are conscious that they have to find a solution to this global problem at the international level. Negotiations on climate change started more than 15 years ago with the signature of the United Nations Framework Convention on Climate Change. Since then, the process went through a series of conferences and protocols. Part of this process, the Kyoto protocol constitutes a major step since it designed country-specific targets defined in terms of CO2 emissions abatement. The fact is that we should not speak about an international environmental agreement ...
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