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
- CO2, N, SO2, H, CO, S, H2S, Cl (in order of decreasing
- 1-4% by wieght, can be greater than 50% by volume.
- different compositions, different abundances.
Nature of atmospheric gases and the contribution of
- 78.08% Nitrogen, 20.95% Oxygen, .93% Argon, .035% Carbon
- standard model - result of volcanic outgassing through
- 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
Lower Cretaceous super greenhouse time:
- much greater extent of basaltic volcanism, and associated
- evidence for concurrent very warm conditions on earth.
Cause and effect?
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