Environmental Geology Lecture - Volcanism and climate change

The basic question here is - what effects can large volcanic eruptions have on global climate? We have clear historic evidence that large explosive eruptions can cause measurable cooling for a duration of several years. The 1991 Pinatubo eruption was a good example. We can also ask -what might be longer term effects? In addition, these questions provide an initial introduction to the myriad of ways that global climate might change.

Character of volcanic gases:

• 60-90% water (juevenile outgassing from mantle vs. recycled from hydrosphere).
• CO2, N, SO2, H, CO, S, H2S, Cl (in order of decreasing abundance).
• 1-4% by wieght, can be greater than 50% by volume.
• different compositions, different abundances.

Nature of atmospheric gases and the contribution of volcanic gases:

• 78.08% Nitrogen, 20.95% Oxygen, .93% Argon, .035% Carbon Dixoide.
• standard model - result of volcanic outgassing through the ages.
• highly modified by biologic activity as evidence the presence of abundant reactive Oxygen.
• possible contribution by small space ice influx.
• major volcanic episodes could change CO2 levels.
• even though a trace gas, major importance (see below).

A model for global climate change:

Some of the myriad of ways to change global climate:

• increase upper atmosphere backscatter:
  • by injection of volcanic sulfur aerosols and ash high into atmosphere (residence time of several years)
  • nuclear winter, large asteroid impacts.
  • change in sea level (interesting feedback loops possible)
• change surface albedo (water, bare land, vegetated land and ice as main surface categories):
  • increase in ice/snow cover and positive feedback cycle (Icebox earth around 600 Ma).
  • deforestation and change in albedo
• change in greenhouse composition:
  • burning of fossil fuels.
  • exchange with oceanic reservoirs.
  • biologic extraction.
  • volcanic contributions out of the ordinary.
• consistent change in cloud cover extent (difficult to model).

Lower Cretaceous super greenhouse time:

• much greater extent of basaltic volcanism, and associated gas release.
• evidence for concurrent very warm conditions on earth. Cause and effect?

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