HR: 15:30h
AN: A43D-10 INVITED     [Abstracts]
TI: Indirect Climatic Effects of Major Volcanic Eruptions
AU: * Hofmann, D J
EM: David.J.Hofmann@noaa.gov
AF: NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States
AB: The direct effects on climate, related to atmospheric emissions to the atmosphere following major volcanic eruptions, are well-known although the sparseness of such eruptions make detailed study on the range of such variations difficult. In general terms, infrared absorption by volcanic emissions to the stratosphere result in local heating early in the event when gaseous sulfur compounds exist. This early period is followed by gas to particle conversion, on a time scale of 1-2 months, promoting the formation of sulfuric acid-water droplets. Coagulation and droplet growth result in the "volcanic stratospheric aerosol layer" which is related to the predominant direct climatic effect of large eruptions, the cooling of the troposphere by backscattering of solar visible radiation to space with a recovery time scale of 1-2 years. In this paper we will discuss some of the less-known "indirect" effects of the volcanic stratospheric aerosol on climate. We label them indirect as they act on climate through intermediary atmospheric constituents. The intermediaries in the volcanic indirect climatic effect are generally atmospheric greenhouse gases or other atmospheric gases and conditions which affect greenhouse gases. For example, cooling of the troposphere following major eruptions reduces the growth rate of atmospheric carbon dioxide related to respiration by the terrestrial biosphere. In addition, redirection of part of the direct solar beam into diffuse radiation by the volcanic stratospheric aerosol stimulates plant photosynthesis, further reducing the carbon dioxide growth rate. The growth rate of the second-most important atmospheric greenhouse gas, methane, is also affected by volcanic emissions. Volcanic stratospheric aerosol particles provide surface area which catalyzes heterogeneous chemical reactions thus stimulating removal of stratospheric ozone, also a greenhouse gas. Although major droughts usually related to ENSO events have opposite effects on carbon dioxide, as have increased emissions by the industrial world, it will be argued that the dearth of major volcanic eruptions since that of Pinatubo in 1991 needs to be considered in explaining the enhanced carbon dioxide growth rates experienced over the past 10 or so years.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0370 Volcanic effects (8409)
DE: 0428 Carbon cycling (4806)
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly