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The general public is familiar with the notion of weather conditions, commonly known as "weather", and weather forecasting on a few days scale. The weather is characterized by several atmospheric parameters of which the best known are the temperature, the wind and the precipitations. The weather can vary greatly from one day to another or from one place to another, even if the two places are close enough. We say that weather is very heterogeneous temporally and spatially.

The climate represents meteorological weather but averaged over long periods, typically at least 10 years. The climate is much less heterogeneous than weather, temporally and spatially. On average, we can see several typical climatic zones, strongly dependent on the sunshine: tropical climates to polar climates and temperate climates to medium latitudes. Meteorological observations and models show that the climate has warmed up over the last 5 decades.

The figure shows an example of atmospheric temperature at the Earth’s surface in January. Temperatures are averaged over the 1959-1997 period. Red areas correspond to a warm climate and blue areas to a cold climate.

Presenter: Slimane Bekki