Quasi-equilibrium in Holocene climatic change

Abstract

To understand man's impact on the environment we should consider the long-term record. Within the Holocene epoch (approximately the last 10 ka), often regarded as having a uniformly mild ‘interglacial-type’ of climate, infrequent but violent fluctuations have disturbed this uniformitarian ideal. A quasi-equilibrium is maintained, however, by powerful feedback mechanisms. The precise nature of both the disturbance-forcing functions and the recovery mechanisms urgently requires study on an interdisciplinary basis, calling for a common-front approach by historians (for the best time scale), by geologists (for establishing the paleoecological and paleogeographical conditions by means of isotopic, sedimentological and stratigraphic studies), and by climatologists (for modelling the meteorological, synoptic conditions that characterize the varied events). Five non-linear forcing agents may be considered in a framework of working hypotheses to help explain the climatic departures: (1) Volcanic eruptions (dust veils and aerosols); (2) lunar and luni-solar tidal effects (variable standing waves in atmospheric pressure, modulation of ocean tides and currents); (3) terrestrial spin-rate and axial tilt (with secular change in precession, the 18.6 year axial rotation and the 1.2 year Chandler wobble); (4) oceanographic and glacial lag factors (influencing the chronology of latitudinal heat transfer; (5) solar radiation modulation of two principal types affecting the corpuscular pulses (solar flares), and the electromagnetic radiation (sunspot and Gleissberg cycles). This paper addresses particularly the last variable because this is the most neglected, and because new information has now become available thanks to new computer-based data sources.