The sequestering (locking up) of carbon in geological formations and removal of carbon dioxide (CO2) from the atmosphere is not a unique, human-driven invention thought up for ameliorating (reducing) the degree of greenhouse gas–driven climate change in the future. CO2 has been spewing from volca- noes on land and the spreading ridges of the ocean throughout geological time. Yet, CO2 levels are not thought to have risen inexora- bly since the Earth was formed some 4.5 bil- lion years ago. Quite the opposite – geological evidence suggests that we live in a period in which atmospheric CO2 concentrations are probably amongst the lowest to have occurred on Earth, at least for the past 600 million years (Royer et al., 2004) (Fig. 6.1a). Indeed, compared to the ‘pre-Industrial’ atmosphere (i.e. immediately prior to the Industrial Revolution c.1765 and the onset of industrialization and increasingly rapid fossil fuel consumption), which was char- acterized by a CO2 concentration of 278 ppm (Enting et al., 1994), geological periods such as the Jurassic (200–145 million years ago) and Devonian (416–359 million years ago) saw about ten times as much carbon residing in the atmosphere. The ocean car- bon reservoir would also have been much larger at times in the past (Ridgwell, 2005)