Introductions:

Purpose of this course:

• motivated by the ongoing vociferous debate.
• desire to understand the issues and data better.
• better understanding of system science.

Course mechanics:

• each week, 1 hour lecture/discussion, 2 hours reading and writing.
• each writing assignment is limited to one page and is worth10 points.
• a straightforward final exam, worth 20 points.
• there is 20 points worth of participation.
• = or > 145 -> A+, <145 to137 is A, <137 to 129 is A-, <129 to 121 is B+, <121 to 113 is B, <113 to 105 is B-, <105 to 97 is C+, <97 to 89 is C, <89 to 81 is C-, you don't want to be lower than this.
• readings will be in PSI room.
• if you have any questions please do not hesitate to contact me.

What are the questions we need to address in a course dedicated to global climate change? If you ask many people whether global warming is occurring they respond as if the question was - is human behavior causing global warming. Those are actually two different questions. Global warming could be occurring, but not due to human behavior. Indeed, it is possible that human behavior could contribute in a significant or insignificant way, and the second question might be better phrased - to what degree is human behavior contributing to any climate change. It is thus important to be explicit about what question(s) is(are) being addressed in a discussion or debate. It can be a productive debate tactic to switch to another related questions, or to purposefully confuse questions, but this is evasion and not science. Use of such a tactic is not designed to try and provide the best answer for the question, but only to 'win' the debate.

• How can global climate change be measured?
• Has global warming been occurring recently?
• If it is occurring what are the causes?
• If it is occurring how much?
• What is the anthropogenic contribution if any?
• What might be future environmental changes related to climate change in the next century?
• With what type of accuracy can we predict future changes?
• How fast can the change occur?
• How will the predicted changes affect people?
• Should humanity take any action?
• What types of actions could we take (planetary engineering)?
• Some links to see the mix.

Important physics: albedo, black body radiation, convection, negative and positive feedback loops.

Ways to theoretically change the energy flux and cause global climate change? Change any of the explicit or implicit relationships between system components above. Simearth! Possibilities are explored below.

Change in energy input:

• change in solar output - .1% documented, more debated.
• change in orbital parameters - Milankovitch (tilt, direction of tilt, ellipcitity). Predictable - long, slow changes and swings.
• stellar dust clouds blocking solar input, unpredictable.

Change in atmospheric albedo:

• cloud cover extent and height.
• sulfur compound aerosols
• volcanism and nuclear winters (impact)

Changes in surface albedo:

• glaciation/deglaciation and attendant sea level rise (note negative feedback cycle).
• deforestation/ forestation
• changes in sea level
• changes in distribution of albedo (continental drift - clearly long term).
• Daisy world.

Changes in atmospheric gas content:

• the greenhouse effect and traces of carbon dioxide.
  • ocean basins, and sediments as major resevoirs.
  • anthropogenic contribution from burning fossil fuels.
  • organic activity (plankton and plant growth).
• other greenhouse gases, e.g. methane. Methane in the tundra?
• changes in resevoir exchange - ocean-atmosphere exchange.

Changes in hydrosphere-atmosphere circulation patterns.

This is rich behavior indeed and geologic history shows the richness of this behavior.

Next time - take a planetary perspective, comparing the history of atmospheres on Earth, Mars and Venus.

Readings:

• Kasting, J. F., Toon, O. B., Pollack, J. B., 1988, How Climate Evolved on the Terrestrial Planets: Sci. American, vol 288, p. 90-97.
• Kargel, J. S. and Strom, R. G., Nov. 1996, Global Climate Change on Mars, Sci. Am., p. 80-88.
• Fairly technical but concise summary from Haberle at NASA, good overview.
• (if you have time) Ingersoll, The Atmosphere, in The Dynamic Earth, Scientific American Book, Freeman, p.81-94.

Discussion question:

What factors may have contributed to the diverging paths of the three planets, Venus, Earth and Mars, and discuss which you believe were the most crucial factors?