There are huge scientific and technical challenges in research directed towards understanding climate and climate change. No clear picture of how the weather and climate system works emerged prior to the 20th century because of the lack of connection between atmospheric variables. In fact, there was still some doubt about deriving a theory about how to interpret daily weather patterns, general circulation of the atmosphere, and the global climate. Atmospheric physics reached a landmark in the early 20th century when empirical climatology, theoretical meteorology and forecasting were about to converge into a conceptualisation of this "vast machine". The problem of understanding the causes of weather, climate and climate change is not one to be solved quickly or easily, but contributing to its solution is particularly worthwhile. In fact, the status of the climate results from the complex interactions between the atmosphere with the physical and biological systems which bound it - the lakes and oceans, ice sheets, land and vegetation through a spectrum of temporal and spatial scales. These elements all determine the state and the evolution of the Earth's weather and climate, owing to a particular influence of the general circulation of the atmosphere which redistributes energy, along with the ocean currents, from the Tropics to the Poles. This highly-coupled system presents a genuine challenge for modellers, and this has led to a body of literature which details the range and hierarchy of numerical climate models.