Volcanic activity and climate

Abstract

From a study of the available reports of volcanic eruptions since A.D. 1500 formulae have been developed for numerical assessment of the magnitude of any eruption in terms of the stratospheric dust veil, using indicators of its optical density, maximum extent over the world and effective duration. These are the aspects of potential meteorological and climatic importance, since they provide some measure of the interference with the solar heating of the earth and the drive of the circulations of atmosphere and oceans. A chronology, with dust veil index assessment, of the eruptions of the last 470 years has been compiled and is published in full elsewhere ( Lamb, 1970 ). It indicates some 45 eruptions since 1680 of a magnitude likely to have had measurable effects (dust veil index ≥ 250, compared with 1,000 for the Krakatau 1883 eruption taken as the standard), including several thought to have exceeded the Krakatau eruption which has been the basis of most investigation and writing on this subject so far. Comparison of these great eruptions, which produced long-lasting dust veils in the stratosphere, with the wind circulation patterns, prevailing temperatures and Arctic sea ice conditions over the succeeding 3–7 years has yielded a number of statistically significant relationships. A cumulative dust veil number is also diagrammatically compared with the course of the main climatic changes of recent centuries as assessed inter alia by probable 50-year mean temperatures in England. These studies make it possible to assess the probable role, and level of importance, of volcanic activity in climatic changes. A very broad, world-wide survey of what is known of the incidence of volcanic activity at various periods in Pleistocene and Postglacial times provides a background which throws further light on this assessment.