The history of our planet is one of climatic change. Geology records the effect of the environment – including climate – on tectonic and geomorphological processes. More recently, the evolution and dispersion of humanity, the development of centres of early civilization, and the rise and fall of cultures have been significantly affected by climatic change.

The oceans have been a crucial, if neglected, part of this history. In the previous chapters we have seen how the ocean and climate are linked in many ways. This chapter will explore how these mechanisms have influenced climatic variability on the varied timescales of Earth's history. For aeons plate tectonics determined the basic climate (§ 6.1). Over the past million years or so cycling in the distribution of solar radiation over the Earth's surface has led to dramatic oscillation in the characteristics of terrestrial and marine environments (§ 6.2). Since the end of the last glaciation significant variability in climate has occurred, much of it affected by air–sea interactions (§ 6.3), and even in the last hundred years such variability is noticeable (§ 6.4). This recent change may be driven by anthropogenic alteration to the environment; Chapter 7 will examine the likely impacts of this new forcing term in our globe's climatic equation and consider whether such predicted changes are yet detectable.