1. Assignment
Volcanic eruptions are a good example of a natural climate forcing mechanism. To prepare you for our module capstone project on the possible effects of a modern day catastrophic volcanic eruption, complete Volcanic Eruptions Part A before coming to class on _##/##/## (the day of unit 6)______

2. A little background on volcanoes
Photo by R. MacKay Mt St Helens from the south, August 2013

3. Plate 1. Schematic diagram of volcanic inputs to the atmosphere and their effects. This is an extended version of Figures 1 and
2 of Simarski [1992], drawn by L. Walter and R. Turco.
from: Allan Robuck, VOLCANIC ERUPTIONS AND CLIMATE. 38, 2 REVIEWS OF GEOPHYSICS , pages AGU Publication (

4. How would a volcanic eruption alter Earth’s mean surface temperature
Volcanic eruption ? Earth’s mean surface Temperature
Take a minute to jot down your ideas in the space below, compare with your neighbor and revise as appropriate, and then be prepared to share with the class.
This is an opportunity for a think pair share referring to the figure on the previous slide.

5. How would a volcanic eruption alter Earth’s mean surface temperature
Volcanic eruption Earth’s mean surface Temperature
The net cooling as volcanic aerosols reduce sunlight reaching the surface is much larger than the increased warming from the added greenhouse trapping from the aerosols. Thus a volcanic eruption is oppositely connected to Earth’s mean surface temperature.
from: Allan Robuck, VOLCANIC ERUPTIONS AND CLIMATE. 38, 2 REVIEWS OF GEOPHYSICS , pages AGU Publication (
Figure suggests that solar cooling is greater than increased greenhouse trapping.

6. And 1991 Mt Pinatubo Eruption Both indicated by vertical lines
Figure from based on meteorological station data. Note that data set is based meteorological stations only as opposed to the land-ocean composite data set investigated in unit 1. This data set was use here to highlight the volcanic signature on global temperatures.
See Krakatoa eruption
And 1991 Mt Pinatubo Eruption
Both indicated by vertical lines

7. What: Large eruption event Approximately 10 km3 (tephra)
10 Gtonnes magma (~ 5 km3)
17 Mtonnes SO2 (USGS)
Eruption: June 12 – 16 , 1991
The abundance of sulfate aerosols created from SO2 and water vapor evolve over time.
SAGE II data figure is from USGS publication From The four 1991 SAGE II images are in sequential order starting from the upper left and ending in the lower right: April10 to May13 (before the June 15 , 1991 Pinatubo eruption); June 15 to July 25 (just after the eruption); August 20 to Sept 30 (3 months after the eruption) ; and December 5 to January 16, It is interesting that the maximum optical depth was reached 3 months after the eruption, as it takes this long for the sulfate aerosols to grow from the emitted SO2 and water vapor.