Volcanos: Global Warmer or Cooler
Country: United States
Date: Spring 2010
Sometimes they say that volcanoes can cause Earth's
temperature to cool because of the sulfur particles in the
atmosphere. other times I hear that they cause warming because of
the build up of CO2. For instance, the theory for initial cause of
the Permian Extinction, was that the eruptions in Russia (basalt?)
caused the earth to heat up due to the increase in CO2. However,
recently in Iceland the same sort of eruptions, to a lesser degree,
occurred and resulted in cooling.
I can understand that shield
volcanoes do not decrease temperature since they are typically not
very explosive. But otherwise, it seems sometimes the same type of
volcanic eruptions are credited with warming and sometimes with
cooling the earth. Could you clarify this for me?
Certainly. The effects are basically as you state, for the reasons
that you state. They act on different time scales.
Sulfates and other suspended aerosols stay in the stratosphere,
blocking incoming solar radiation, for a year or so. Even though
the stratosphere is very stable compared to the troposphere (the
atmospheric layer in which we live), the suspended particles do
eventually settle out on the time scale of a year or so.
Currently, carbon dioxide has a residence time in the atmosphere of
about 100 years. So let us say that we have major volcanic
eruptions every five years or so. So every five years there will be
a year of cooling due to volcanic aerosols, which soon
dissipate. Over time, though, carbon dioxide accumulates, making a
long-term warming trend.
The Permian extinctions may be related to an upsurge in
volcanism. There were also Precambrian episodes of extreme global
cooling ("Snowball Earth") that are thought to have been ended only
by radiation trapping by accumulated volcanic carbon dioxide. In
the "Snowball Earth" case, the residence time of CO2 was much longer
than it is not, because the icy conditions were not very conducive
to carbon dioxide-consuming photosynthesizers. So, over the eons,
the carbon dioxide could accumulate, and accumulate, until it tipped
Earth's the climate regime. Any temporary effect of volcanic
aerosols in the long run was overwhelmed by the greenhouse accumulation.
So, in summary, the issue is one of time scale. The different
processes operating on Earth, such as photosynthesis, biomass
burning, fossil carbon release, carbonate weathering, and so on
affect the time scale of the different processes, and they can also
"feed back" in complex ways.
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
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