GEOLOGICAL CONSTRAINTS ON GLOBAL CLIMATE VARIABILITY

Abstract

Anthropogenic forcing of global climate is a concept with great political appeal but generally ignores basic concepts of science, particularly geological knowledge. Much of the current popular debate focuses on decadal variation in global temperature and ignores the natural variability inherent in geological records ranging in scale from centuries to eras. Discussions about geological constraints require understanding that geological science views the earth processes as being in disequilibrium, geology is a temporal science, and the energy budget of the earth is controlled by radiogenic and solar inputs creating a single dynamic Earth system. One illustration of the geological constraints on global climate is the congruence of widespread glacial episodes (icehouses) and warm periods (greenhouses) with continental plate configurations. During icehouse events (Late Precambrian, Carboniferous, Neogene), continents are arranged so as to disrupt equatorial ocean currents, distributing heat unevenly and providing polar moisture to sustain large-scale glaciers. During greenhouse events, earth-circling equatorial currents are presumed from lack of physical barriers. The conclusion is that tectonic distribution of topography and placement of continents control the geometry of ocean currents which in turn determine Earth climate.