By now it should be obvious that there are a lot of things that can contribute to changes in the climate. So assessing the causes of these fluctuations opens up a huge variety of physical processes. To keep this analysis manageable we must concentrate on the most obvious factors, and then focus on how these may contribute to future climatic trends. This means we will consider both short- and long-term processes in seeking explanations of natural variability. Then the analysis will narrowed down to the causes of more rapid fluctuations when the question of the impact of human activities is brought into the debate. So, the principal objective will be to identify those aspects of climate change that provide the most insight into how the global climate may change in the foreseeable future.

Particular attention will be paid to mechanisms for climate change which have cyclic properties. This emphasis is not based on the fact that the evidence of periodic behaviour is stronger than other forms of change but because the linking of cause and effect is easier. This is a consequence of both the ability to attribute cyclic variations to a specific cause when an a priori reason (see Section 5.1) is identified for the periodicity to occur and then to examine a physical link between observed fluctuations and their postulated cause.