CLIMATE AND GEOLOGY - A PHANEROZOIC PERSPECTIVE

Abstract

The Phanerozoic is comprised of over 540 million years and, with its defining accompaniment of abundant complex life, provides us with a unique perspective on the extremes of climate change. Understanding these extremes is particularly important if we are to anticipate the possible effects of global warming. The broad sweep of climate change through the Phanerozoic began with relatively cool global temperatures and recovery from late Proterozoic glaciation. This was followed by a mid-Cambrian to Ordovician episode of relatively warm global climate, after which global climate cooled, culminating in the major glaciations of the Carboniferous and Permian Periods. The Triassic and Early Jurassic were warm. The Late Jurassic-Early Cretaceous Period was cool, although without full global glaciation. Global temperatures peaked in the mid-Cretaceous. Since then, global climates have cooled, culminating in Neogene glaciation. These c. 100-million-year trends in overall climate show short intense excursions of contrasting climate, many of which have been associated with the mass extinction of life, and with major volcanic and tectonic events. This paper argues that, through the Phanerozoic, two overlapping stable climate regimes appear to have dominated: a bigh-CO2 (> 1000 ppmv), largely warm climate regime, punctuated by many short-lived episodes of glaciation; and a low-CO2 (< 1000 ppmv), largely cool regime, marked by protracted episodes of superglaciation.