Multiplicity of Time Scales in Climate and the Earth System

The Earth system is highly complex and fascinating. It ranges from the upper atmosphere into the solid Earth, and it is influenced and interacts with the solar system and even further into space. Here, some of the main elements in the system are categorized, and a number of phenomena taking place on many different time scales are described: even if one only considers phenomena occurring on spatial scales larger than molecular, it turns out that timewise the system covers about 19 orders of magnitude, i.e., a very pronounced multiplicity of time scales. Humans have only been active players for relatively few thousand years in this system. However, our role has been growing rapidly. Therefore, the chapter has special emphasis on understanding and to some extent also modeling phenomena of importance for the impact of anthropogenic activity in the Earth system. It is argued that humans have begun to act as important players in a system that appears to be more fragile than believed by most. This is a system where fundamental time scales are now directly influenced by us, i.e., with considerable potential future impacts.