The energy budget at the Earth’s surface is an important thing to quantify because any imbalance will result in compensating changes in temperature. Primarily, the balance is between incoming solar radiation, outgoing terrestrial radiation, and radiation “trapped” in the atmosphere by the greenhouse gases (GHG’s: water vapor, carbon dioxide, methane, and nitrous oxide are the main ones).
On long timescales (hundreds of thousands to millions of years), climate is influenced by:
- distance from the sun and intensity of the sun,
- atmospheric composition (especially how many GHG’s there are),
- tectonics (locations of continents and oceans affect atmospheric and oceanic circulation patterns),
- Earth’s orbital path around the sun,
- volcanism (volcanoes emit GHG’s, although on the timescale of 1-2 years they have a cooling effect because the particles they emit also reflect solar radiation).
On short timescales, regional climate is determined by:
- the variation of solar radiation with latitude
- distribution of land and water (water retains heat through the winter because of its high heat capacity, while land has large temperature variations from winter to summer)
- ocean currents
- prevailing winds
- persistant high and low pressure areas (high pressure areas have sinking air that is warm and dry, low pressure areas have rising air and storminess)
- mountain barriers (rainy on the upwind side, dry on the downwind side)
- altitude
A lot of what we talked about was this general overview type information. It is what you would learn in a climate 101 course over the first few weeks, but we did almost all of it in one day – joy! More of this information can be found at: http://www.cmmap.org/learn/climate/causes1.html.
Activities today: A HW on what determines climate for different regions (similar to this map: http://www.cmmap.org/learn/climate/causes7.html. And a lab using a simplified model, which calculates the average surface temperature based on some of the 'long-term' climate forcings. It can be downloaded here: http://icp.giss.nasa.gov/education/geebitt (go for Mini-GEEBITT version B3).
Reading: We had them read Ch 2 from Ruddiman's textbook: Earth's Climate, Past and Future. I think this is a good textbook, but we chose to use papers for most of the class reading. Luckily, this chapter is available on the publisher's webpage (for now at least!). Also, there is a short paper by Jim Hansen from Science 2005 called: Earth's Energy Imbalance: Confirmation and Implications. It is a little meaty for the first day of a class, but I think it's a good overview of how the Earth's energy isn't balanced due to increasing GHG's in the atmosphere. So it helps set the stage for things we'll talk about later in the course.
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