The Role of Volcanic Activity in Climate and Global Change

The Role of Volcanic Activity in Climate and Global Change

The Role of Volcanic Activity in Climate and Global Change
G. Stenchikov
Climate change: Observed Impacts on Planet Earth, Chapter 4, Elsevier, (2009)
G. Stenchikov
Climate change
2009
Volcanic activity is an important natural cause of climate variations because tracer constituents of volcanic origin impact the atmospheric chemical composition and optical properties. This study focuses on the recent period of the Earth’s history and does not consider a cumulative effect of the ancient volcanic degassing that formed the core of the Earth’s atmosphere billions of years ago. At present, a weak volcanic activity results in gas and particle effusions in the troposphere (lower part of atmosphere), which constitute, on an average, the larger portion of volcanic mass flux into the atmosphere. However, the products of tropospheric volcanic emissions are short-lived and contribute only moderately to the emissions from large anthropogenic and natural tropospheric sources. This study focuses instead on the effects on climate of the Earth’s explosive volcanism. Strong volcanic eruptions with a volcanic explosivity index (VEI) equal to or greater than 4 could inject volcanic ash and sulfur-rich gases into the clean lower stratosphere at an altitude about 25–30 km, increasing their concentration thereby two to three orders of magnitude in comparison with the background level. Chemical transformations and gas-to-particle conversion of volcanic tracers form a volcanic aerosol layer that remains in the stratosphere for 2–3 years after an eruption, thereby impacting the Earth’s climate because volcanic aerosols cool the surface and the troposphere by reflecting solar radiation, and warm the lower stratosphere, absorbing thermal IR and solar near-IR radiation.