Volcanoes as agents of past environmental change

In recent years a sequence of papers has discussed the impact of volcanic eruptions upon global environments. Emphasis has been placed upon their potential role in depressing hemispheric temperatures and affecting global weather patterns. Many researchers have related ecological, environmental and historical phenomena to individual eruptions. However, the linking of spatially and temporally disparate phenomenon to eruption chronologies involves several levels of supposition and at each level in the argument greater potential for error arises. This paper examines critically a number of important issues that arise from these studies. How valid are the linkages that are drawn? Do they establish a dependent relationship or merely coincidence? The validity of linking volcanic activity with disparate spatial and temporal events in the climatic, historical and palaeoecological records is addressed. There can be little doubt that volcanoes have a great effect on proximal climates and environments, but their global impact is less well understood. The scale and magnitude of responses to large eruptions such as the historically notorious Tambora (1815) and Mt. Pinatubo (1991) is far from consistent. This paper urges the adoption of a more critical perspective when considering these issues.