Climate: Is the past the key to the future?

Abstract

The climate of the Holocene is not well suited to be the baseline for the climate of the planet. It is an interglacial, a state typical of only 10% of the past few million years. It is a time of relative sea-level stability after a rapid 130-m rise from the lowstand during the last glacial maximum. Physical geologic processes are operating at unusual rates and much of the geochemical system is not in a steady state. During most of the Phanerozoic there have been no continental ice sheets on the earth, and the planet's meridional temperature gradient has been much less than it is presently. Major factors influencing climate are insolation, greenhouse gases, paleogeography, and vegetation; the first two are discussed in this paper. Changes in the earth's orbital parameters affect the amount of radiation received from the sun at different latitudes over the course of the year. During the last climate cycle, the waxing and waning of the northern hemisphere continental ice sheets closely followed the changes in summer insolation at the latitude of the northern hemisphere polar circle. The overall intensity of insolation in the northern hemisphere is governed by the precession of the earth's axis of rotation, and the precession and ellipticity of the earth's orbit. At the polar circle a meridional

Isotopic and chemical intra-shell variations in low-Mg calcite of rudist bivalves (Mollusca-Hippuritacea): disequilibrium fractionations and late Cretaceous seasonality

“…This agrees with mean equatorial palaeotemperatures of 27-32 7C reported from magnesian calcite and aragonitic rudist remains from Maastrichtian platform carbonates of a Pacific guyot (Wilson and Opdyke 1996), as well as with predictions of Cretaceous climate from general circulation models (Barron et al 1995;Bush and Philander 1997;Hay et al 1997). Extremely warm surface waters from the Turonian through the early Campanian of the southern high latitudes are evident in d 18 O of planktonic foraminifera (Huber et al 1995).…”

The Frasnian–Famennian biotic crisis: How many (if any) bolide impacts?

“…In particular, some reasons for the KW crisis, given by Copper (1998), may be of limited significance in the "peculiar" Devonian World (by Quaternary standards) under tremendous global stress (Ormiston and Oglesby 1995;Harries et al 1996). It is well shown for complicated relationships in greenhouse/icehouse climate states (Hay et al 1997). Further study would be particularly meaningful in the context of volcanogenic/geothermal upwellings and overturns, in links with recently favored F-F scenario of paired anoxia and transgression (see a summary in Hallam and Wignall 1997).…”

“…Liu and Schmitt 1996, p. 991). All the factors have resulted in the puzzling but perhaps pulsatory climatic evolution on a shorter time scale (e.g., Buggisch 1991;Hay et al 1997).…”

The future of coral reefs in an age of global change

“…This suggestion is supported by both climatic and geological history. Our current interglacial climate, which appears to be particularly favorable for reef carbonate deposition and preservation, is representative of only 10% of the past few million years (Hay et al 1997;Pearson and Palmer 2000). Based on reconstructions of past CO 2 atmospheric concentrations (Berner 1994(Berner , 1997, the currently low CO 2 concentration is atypical for most of Earth's history.…”