Use of paleo-records in determining variability within the volcanism-climate system

Volcanic eruptions that inject large quantities of sulfur-rich gases into the stratosphere have the capability of cooling global climate by 0.2-0.3 degrees C for several years after the eruption. Equatorial eruptions will impact global climate whereas mid-latitude eruptions can cool climate in the hemisphere of origin. Magnitude of cooling varies by latitude and it is possible for warming to occur in certain regions, primarily during the winter. Although instrumental records have been used to quantify the volcanic impact on climate, they are limited in their temporal and spatial coverage, and the style and magnitude of eruptions occurring over the two centuries of instrumental records is limited. A thorough evaluation of the range of variability in the volcanism-climate system requires a multidisciplinary approach that includes the analysis of ice core records, geological data, atmospheric measurements and visual phenomena, tree-ring records and other proxy data. Evaluation of these longer time series indicates that multiple volcanic eruptions have the potential to force climate over decadal to multi-decadal time frames, especially when these eruptions enhance or extend pre-existing cool conditions. On the other hand, a lack of climatically significant eruptions may result in warmer average temperatures over decadal time frames because the volcanic-cooling component within the climate system is absent. Mega-eruptions, like the Toba eruption of similar to 71,000-73,000 yr ago, may impact climate on centennial time frames through positive feedback mechanisms. Evidence exists which indicates that environmental changes associated with rapid climatic fluctuations, such as crustal loading/unloading with glaciation/deglaciation and variability in glacial meltwater loading on ocean basins, may cause an increase in volcanic activity. (C) 1999 Elsevier Science Ltd. All rights reserved.