Tuesday, January 20, 2012 CC-BY-NC
L4 - alternate

Maintainer: admin

Lec 2 - Geog 205


  • readings if you missed the first two lectures

2why does the climate change?

  • consider earth's orbit, solar strength, the amount that makes it through, how much is absorbed, and how much is reflected
  • these systems interact:

3recall energy balance - green house effect

  • know the chart really well
  • 109% absorbed (accumulation)

4earth's mean temperature

  • if we look from 1940 to 1975, there is a cooling trend
  • the cause: sulfur dioxide : is an aerosol that reflects sunlight
  • around mid 70's, legislation reduced mat of sulfer dioxide

5possible causes of climate change

  • external forcing: greenhouse gases, tropospheric aerosols (reflect sunlight), land use change, long-term solar radiation (how close earth to sun, angle, energy emitted by sun)
  • internal variation: thermohaline circulation (i.e. conveyor belt) ( change the balance), and el nino (short term)
  • 29.1why do we care about short-term? perturbation, feedback, land use. we also need to make sure that our short term knowledge is predictable

6correlation does not imply causation (obviously)

  • must understand theory bfore we make relationships

7testing the causes of climate change

  • look for correlation (external force changed in a similar way as observed climate?
  • scientific explanation?
  • dominate cause?

8greenhouse gases

  • ppm composition of earth's atmosphere (will be on exam)

  • need to look at lifetime of gases,

  • lifetime: i.e. respiration, recycling multiple lifetimes
  • methane lasts 12 years,
  • global warming potential: if co2 is one, ch4 has larger impact
  • co2 is dominate, i.e. it has most effect + most numerous

9where do gases come from?

10water vapor

  • natural hydrological cycle
  • but as climate changes, the amount of water vapor increases

  • has to do with the amount of energy in atmosphere to evaporate water from the oceans


  • breathing, fossil fuels, livestock
  • also natural sources, like soils


  • anaerobic respiration, microbes release methane
  • cattle farts

13nitrous oxide

  • fertilizer


  • when produced in troposphere, is bad (for some reason)


  • ideally replaced


  • replaced CFCs

17are current levels of greenhouse ages increasing?

  • 3 major: carbon dioxide, methane, nitrous oxide

18where is warming occurring?

  • warming at the top at the troposphere

19how do we know co2 comes from humans?

  • isotopes. c12, 99%. c14, radioactive, used for carbon dating, are decaying
  • c14 is decreasing. c12 is increasing. this means that c14 hasn't been used in a long time
  • c14 possibly from fossil fuels or volcanos
  • c13 possibility. plants have lower c13 than geological sources.
  • there are more sources of organic carbon in atmosphere
  • thus, we deduce that cause of increase of carbon is fossil fuels


  • which planet in the solar system has a runaway greenhouse effect? i.e. positive feedback
  • answer: venus
  • venus doesn't absorb very much energy
  • 96% atmosphere is co2, and greenhouse gases are 265 deg f

21topospheric aerosols

  • sulfates, soot, organic carbon, dust
  • tend to be short lived
  • esp in troposphere, precipitated out by rain
  • but when reach stratosphere, they can last for years
  • aerosols form a haze
  • they reflect the sunlight away (or something)
  • volcanic activity, dust from desert, manufacturing


  • mount pinatubo
    • spread around the globe, for several years
    • decrease in 4 w/m^2, decrease in 1% of solar radiation globally

23long-term solar radiation variations and 11-year sunspot cycles

  • at about 100,000 year cycle from circular orbit to elliptical earth orbit
  • but this doesn't match our sudden increase of temperature
  • tilt and wobble- changes in earth axis
  • -- right now we're in the middle
  • -- distribution of temperatures would change
  • -- wobble changes the time that the season occurs
  • time scale: 20,00 - 100,000 years, not responsible for short time scale


  • increase over time.
  • less sunspots, less solar radiation
  • sunspots: change 2% of radiation. compare to mt petuba, is 1/8th

25land use change

25.1- directly effects albino(?)

26thermohaline circulation (probably on exam)

  • major movements of energy from tropics to poles
  • some other stuff

27el nino (classic example)

  • between 3 and 7 years, it happens
  • heating and cooling
  • when it occurs: southeast trade winds revere or weaken, cold upwelling reduced or absent, high pressure over austrilia, rain over south america
  • changes weather patterns across the world
  • also, La Nina, like El Nino, but less strong
  • about a redistribution of global climate, but not a signal.

28galapagos islands

  • dry and wet seasons
  • warm water is nutrient poor, wreaks havoc on marine ecosystems

29from all the possible effects …

  • total radiative forcing, co2 and ch4 have the greatest effect