Chapter 6 - A Geological History of Climate Change

Abstract

Earth's climate is now changing in response to an array of anthropogenic perturbations, notably the release of greenhouse gases; an understanding of the rate, mode, and scale of this change is of vital importance to society. Presently intense studies of current and historical changes in both perceived climate drivers and the Earth system response are being carried out. Such studies typically lead to climate models that, in linking proposed causes and effects, are aimed at allowing prediction of climate evolution over an annual to centennial scale. The history of Earth's climate system, as deduced from forensic examination of strata, has shown a general very long-term stability, which has probably been maintained by a complex interaction between the biosphere, atmosphere, hydrosphere, cryosphere, and lithosphere. Superimposed on this overall stability has been a variety of climate perturbations on timescales ranging from multi-million year to sub-decadal, inferred to have been driven by variations in paleogeography, greenhouse gas concentrations, astronomically forced insolation, and inter-regional heat transport. Current anthropogenic changes to the Earth system, particularly changes in the carbon cycle, are geologically significant. Their effects may likely include the onset of climate conditions of broadly pre-Quaternary style such as those of the “mid-Pliocene warm period,” with higher temperatures, substantially reduced polar ice cover, and modified precipitation and biotic patterns.