The global climate is warming. The most likely cause behind the warming in the latter half of the twentieth century is the emission of greenhouse gases from human activity. If the emissions continue to increase at the present rate we can expect a warming in this century well beyond what we have experienced so far. A continued global warming may seriously threaten human societies as well as the global economy.
The modelling tools used to investigate climate change are based on physical laws, classical mechanics and thermodynamics as well as modern quantum physics form the fundamental prerequisites on which climate models are built. In addition, we need observations of the physical climate system using advanced techniques such as satellite based remote sensing and in-situ observing platforms such as aircrafts and balloons. Observations and theory are combined using mathematical models and supercomputers. The global climate is described as a dynamical system that we can use both to understand the past and to make predictions of the future.