Studying Past Volcanic Activity with Tree Rings

Abstract

A volcano is an opening in the Earth’s crust from which hot magma, ash, and gases escape to the surface. Volcanic eruptions produce numerous and dramatic environmental changes from very local to global scales. Strong explosive eruptions ejecting sulfur aerosols in the stratosphere can impact the Earth’s radiation balance, and hence, surface temperature as well as atmospheric circulation patterns. The radiative effect and related cooling after explosive, especially tropical, eruptions is stronger in summer. In the cold season, on the contrary, eruptions generally lead to warming due to an enhanced pole-to-equator gradient and subsequent change in circulation mode. The maximum global cooling (0.1–0.2°C) occurs approximately one year after a strong tropical explosive eruption and the degree of this cooling follows the solar declination displaced toward the north. The eruptions occurring in the high latitudes (e.g. Laki in 1783), on the contrary, reduce the pole-to-equator temperature gradient and lead to the cooling even in winter. Another important effect of this type of eruption is the failure of the summer Indian monsoon (Robock 2000).