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This issue of the pace of the recovery JnAn angry wind blows on the Congress of the CFDTThe adoption of Office is thus facilitatedIt was built from the beginning by de Gaulle himselfTurnover nonnews release gross margin 2The first concerns the status of European mutualBankers have also been questionable ethically27 point per year in the reform of pensionsIn this field the Mayor is clearly liableOnce more music by Randy Newman is fallingScientists do have sufficient technical means to understand and predict climate change The question is no longer debate among specialists in mechanics of fluids and thermodynamics. "The number of mathematical uncertainties in models of simulations is such that it necessarily affects the realism of the results," recognizes Bernard Fontaine, Director of the Research Centre of climatology at the University of Bourgogne. In the dock: imperfect modeling of clouds, fragmented understanding of biogeochemical cycle, insufficient regional resolution of the models, impact unknown to natural variability, climate change past insufficient history... "The consensus developed by experts from the IPCC relies on a bed of doubt", is a British expert.
6 million of variables
To establish a prospective to body, scientists confront the simulations provided by twenty-three models developed by meteorological institutes and university research centres to represent the evolution of the climate in a succession of equations and complex algorithms. Is several billion operations per second, the calculations paint dynamics of fluid on the surface of the globe since the ocean depths to the boundaries of the stratosphere, with a constant: the conservation of mass and energy, the keys of the climate system components determining the exchanges between its components.
This schematic representation of the movements of air and water backs to a large number of variables such as pressure, temperature, density, moisture, whose values change every second on the surface of the globe. Not to mention the external settings - called "forcings" - which may have a temporary influence on the initial data: concentration of aerosols, solar intensity variation, volcanic activity...
Impossible to calculate precisely on a global scale the interactions between all these elements. Conceptual models created to simplify this work are therefore based on a schematic representation of the movement of the fluid on the planet. The weather France, Arpège, divides the globe in 24.572 mesh of hundreds of kilometres apart, and more than 30 levels up to the lower stratosphere. "It takes into account some 6 million of variables", describes Serge Planton, responsible for climate research group. To treat them, Arpège is not less than 4 million lines of computer code. "Total says its leader, Michel Déqué, the writing of this software has mobilized 100 years-man and the experience of our meteorologists for twenty years."
The problems of the clouds
What does step of imperfections, common to all models. "Our main weak point is the extent of the radiative properties of clouds," recognizes Serge Planton. A scientific impasse in reality. With the help of lasers and satellite measurements in programs like Calypso or CloudSat, researchers attempt to for years to develop a universal law on the optical properties of large air masses. The objective is to infer the process who interact with the solar radiation clouds and greenhouse gases. Lost sentence. "Simulations are very imperfect on this point," confirms Olivier Boucher, who heads the laboratory environment, chemistry and ecosystems to the Hadley Center, the research centre of the British Met Office. We know for example that, due to their scope, clouds low and shallow subtropical oceans play a particular role in the radiative balance of the models, i.e. the difference between absorbed solar energy and that returned by the Earth. But how much
"Each interpreting,"says Serge Planton." The effect of clouds is an intuitive parameter that depends on the sum of knowledge and beliefs of the team operating the model. "It is one of the main points of divergence of climate projections. If all agree on the increase in the Earth's temperature, consensus does not on assumptions of future rainfall, particularly in tropical regions.
To refine simulations, researchers have therefore had the idea of combining their general circulation models of the atmosphere, oceans and ice floes, to more localized simulation tools. "These new models must be powered by specific observations made on the ground at the desired level, Paris intramural or the Mediterranean basin for example, explains Bernard Fontaine." "Measurement campaigns will therefore be the issue of the relevance of future simulations," he said.
Climatologists, wherever they may be, already have access to the observations of the satellites provided by the NOAA (National Oceanic and Atmospheric Administration), a federal agénce of the U.S. Department of Commerce. But the considered mesh is overall too approximate. "Missing still measures amount to feed the models", said Bernard Fontaine. One of the essential data, and another source of dispersion of the results, is the measure of the carbon cycle. "It is one of the major shipyards of the simulation," confirms Serge Planton. One of the objectives is to determine how the natural carbon sinks - oceans and the continental biosphere - will be affected by climate change, and what are the consequences for the climate.
Several programmes have been launched to develop the atlas expected, such as Fluxnet, a network of more than 400 weather towers which measure the exchanges of carbon dioxide, of water vapour and of energy between terrestrial ecosystems and the atmosphere. Results are also expected from the "Millenium experiment" site which will search the paleoclimatic archives to create a metre standard models for biogeochemical cycle (read below).
These knowledge will remain to climatologists to meet another challenge: find sufficient calculations capabilities to deal with the huge mass of variables.
