Volcanism and global climate change
Benjamin Franklin (1784) suggested that that year's severe
winter was the result of eruptions in Iceland and Japan: Laki
flow in Iceland emitted very large sulfur gas clouds, which locally
decimated livestock. This was a grim time in Iceland's history.
The basic correlation between volcanic eruptions and global weather
pertubations had been made. The mechanism was not understood.
Mechanism by which volcanism effects climate?
What are important factors determining the amount of cooling
from a large explosive eruption (discussion question)?
Historic eruptions, case histories.
Mt. Pinatubo :
- 20 million tons of sulfur dioxide in 9 hour long climactic
eruption up into stratosphere to an altitude of 20 miles.
- sulfur reacts to form sulfuric acid, which stays lofted as
a fine aerosol.
- the lower atmosphere cools because of reduced solar input.
- the stratosphere actually warms since sulfur aerosols also
absorb radiant heat from below.
- maximum cooling effect estimate by USGS (Open File Report
97-262) at 1.3°C
- 13 cubic miles of ejecta, up to 50 miles attitude
- local complete darkness for days
- Montpelier Observatory in Europe - 20% drop in direct solar
radiation, at 10% below normal for 3 years.
Why are these short lived? Residence
time - there are processes that remove the sulfur aerosols from
the atmosphere: settling and chemical reactions. Readings describe
Climate effects of asteroid impacts:
- nuclear winter and impact hypothesis for extinction.
- a lot of debate as to efficacy.
The geologic record and the effect of volcanism
Is the rate of volcanism on the earth a constant on the
earth at any time scale?
- can think of our smoothing methodology - what size sliding
average window would you need before have a sraight line?
- the evidence is clear that it is not at a scale of even 10s
of millions of years - the earth pulses as indicated by your
- this is why a narrow uniformitarian approach is unnecessarily
Could a volcanic eruption or series of eruptions in concert
with other factors contribute to a climate shift (the last straw
What is largest eruption that could happen?
Where is majority of volcanism occurring on earth at present?
K superplume event: huge Aptian-Albian (120-100 Ma) increase
in ocean crust formation (75% increase over present rates). This
corresponds to one of the most stable and warmest geologic periods
on record. Why associated with warming and not cooling? Filtering
effects of oceans? Yo-yo effect?
Is volcanism a major factor in present debate about global
climate change? Should it be?
The best indicator of the range of possible
future behavior is past behavior. Considering this it is useful
to think of all the places that might have a paleoclimate record?
- ice cores.
- lake varves and pollen.
- deep sea muds and shells.
- the temperature in the ground.
- will see that isotopic chemistry a key.
Discussion question for next time: How do the results
from the boreholes compare to those of meteorologic records from
last 200 years or so? Be as specific as possible. Why is it important
to make such a comparison.
Readings for next time:
- Pollack, H. N. & Chapman, D. S., 1993 (June), Underground
records of changing climate, Scientific American, 44- 50. Focus
in on this one.
- Pollack, H.N., S. Huang, S. and P. Shen 1998. Climate change
record in subsurface temperatures: a global perspective. Science,
282, 279-81. If you have time and interest, read this one.
& report on ongoing research "Climate Change in the
Mid-Continent of North America ".