The difficult question of forecasting | Tangente

Global warming caused by CO₂ cannot be calculated without a coupled atmosphere–ocean model, now made possible by the growing power of computers. This core component of climate simulation lies at the heart of the twenty to thirty existing climate models. A grid cell is a parallelepiped measuring 100 to 200 kilometres along two sides, whose vertical dimension becomes progressively smaller nearer the Earth's surface. The discrepancies regularly observed between models, particularly during international model intercomparison exercises, are often due to subgrid-scale phenomena that play a key role at scales smaller than the grid cells: radiative exchanges, vegetation, atmospheric turbulence, the role of clouds, aerosols and water vapour, ocean currents… For example, the slowdown in ocean circulation in the North Atlantic, linked to reduced salinity as precipitation increases, makes it harder to predict what will happen along France's western seaboard.