Weather and climate have a profound influence on life on Earth. The weather is the fluctuating state of the atmosphere around us. The climate is the 'average weather' (more rigorously, it is a statistical description of weather, including variability and extremes as well as averages); climate involves the other components of the climate system in addition to the atmosphere.
Components of the climate system
The atmosphere: its circulation, the heat (terrestrial radiation) and light (solar radiation) which pass through it, and the processes which go on in it, such as the formation of clouds and the atmospheric chemical reactions that determine the concentrations of some of its important constituents, such as methane and ozone.
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The ocean: There is a constant exchange of heat, momentum and water between ocean and the atmosphere. The ocean acts as a heat sink to delay climate change. In addition, ocean currents transport large amounts of heat and water around the world. The land surface, including its vegetation and seasonal snow cover, has an important influence on the flow of air over it, the absorption of solar energy, and the water cycle. The cryosphere: those parts of the world whose surface is affected by ice, principally sea-ice in the Arctic and Southern Oceans and the land-based ice-sheets of Greenland and Antarctica. The biosphere: Life on land (the terrestrial biosphere) and in the ocean (the marine biosphere) play a major role in the carbon cycle and hence in determining the atmospheric concentration of carbon dioxide. |
Climate models
In order to make predictions of climate change, we have to calculate the effects of all the key processes operating in the climate system. Our knowledge about these processes can be represented in mathematical terms, but the complexity of the system means that the calculation of their effects can only be performed in practice using a computer. The mathematical formulation is therefore implemented in a computer program, which we refer to as a climate model. Various types of climate model are used at the Met Office Hadley Centre and elsewhere for climate simulation and prediction. The limitations of our knowledge and computing resources mean that the results of climate models are always subject to some uncertainty.
