Climate System Dynamics and Modelling

The climate has a significant impact on life on Earth as well as on human activities. Temperature and precipitation strongly constrain the type of vegetation that can grow in a particular region. The design and location of houses depend on summer and winter temperatures and also on the probability of flooding. One single, late frost or a heavy hail storm could ruin an entire crop. Since the beginning of humanity, people thus have had to cope with climate and, if possible, to adapt to it. As a consequence, the various human civilisations have observed and tried to understand climate variations. They first provided mythological or religious explanations, often relying on weather lore to obtain forecasts. In parallel, climate has evolved as a science, elaborating more and more sophisticated representations of the observed phenomena. Such a description of climate now involves a very broad range of expertise corresponding to different domains of the sciences, including physics, chemistry, biology and geology.

A comprehensive analysis of all the components of the climate system (i.e., atmosphere, ocean, ice sheets, land surfaces, etc.) and of all the interactions between them is beyond the scope of any course or book. Here I provide only a relatively brief overview of the processes that rule the behaviour of the individual components. More detailed descriptions are provided in meteorology, oceanography and glaciology textbooks, for instance, with some suggestions for reading given in the reference section. The focus of this book is on the interactions between the different elements of the climate system and on the main feedbacks that govern climate variability on all the time scales. On this basis, the first goal of this book is to analyse the dominant causes of past climate changes and to critically discuss the projections of climate change over the next centuries or millennia.

Because of the complexity of the system, many analyses devoted to a quantitative estimate of climate change or climate variability rely on the use of comprehensive three-dimensional numerical models. Simple models are also widely applied to underline clearly the fundamental properties of the climate.