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)?

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

Krakatoa: 1883

• 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.

Tambora, Indonesia

Climate effects of asteroid impacts:

• digression
• nuclear winter and impact hypothesis for extinction.
• a lot of debate as to efficacy.

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 reading.
• this is why a narrow uniformitarian approach is unnecessarily restrictive.

Could a volcanic eruption or series of eruptions in concert with other factors contribute to a climate shift (the last straw hypothesis)?

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?

• ice cores.
• lake varves and pollen.
• speleothems.
• 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.
• Gosnald & report on ongoing research "Climate Change in the Mid-Continent of North America ".