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2 6-2003-1


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2 6-2003-1

  1. 1. Last ClassHow does variability in the earth’s physical structure affectthe transformations of energy? - albedo of different “spheres”; cloudsWhat is the physical structure of the atmosphere? - multi-layered, with little chemical interaction - most of the mass is near the surfaceWhat is the chemical structure of the atmosphere? - nitrogen by far the most common element - oxygen is second most common - greenhouse gasses are small in amount, but important!
  2. 2. Structure of the Atmosphere Thermosphere Mesosphere Ozone Maximum Stratosphere Troposphere Temperature
  3. 3. How does energy input to the earth surface vary across the globe?
  4. 4. This Class - The Green House Effect and Global Warming How is energy distributed to the earth’s surface? What are greenhouse gases and the greenhouse effect? Impact of an increase in atmospheric CO2 on greenhouse effect Recent changes in greenhouse gas concentrations Relationship between the greenhouse effect and global warming
  5. 5. The “Greenhouse Effect”The Earth’s surface thus receives energyfrom two sources: the sun & theatmosphere– As a result the Earth’s surface is ~33°C warmer than it would be without an atmosphereGreenhouse gases are transparent toshortwave but absorb longwave radiation– Thus the atmosphere stores energy
  6. 6. Electromagnetic Spectrum incoming outgoing
  7. 7. 1. Shorter, highEnergy wavelengthsHit the earthsSurface2. Incoming energyIs converted to heat
  8. 8. 3. Longer, infraredWavelengths hitGreenhouse gasMolecules in theatmosphere4. Greenhouse gasMolecules in theAtmosphere emitInfrared radiationBack towards earth
  9. 9. 78% nitrogen20.6% oxygen< 1% argon0.4% watervapor0.036% carbondioxidetraces gases:Ne, He, Kr, H, O3Methane, NitrousOxide
  10. 10. Absorption Spectra of Atmospheric Gases Visible UV Infrared CH4 N2O O2 & O3 CO2 H2O atmosphere WAVELENGTH (micrometers)Anthes, p. 55
  11. 11. Selected Greenhouse Gases• Carbon Dioxide (CO2) – Source: Fossil fuel burning, deforestation Anthropogenic increase: 30% Average atmospheric residence time: 500 years Methane (CH4) – Source: Rice cultivation, cattle & sheep ranching, decay from landfills, mining Anthropogenic increase: 145% Average atmospheric residence time: 7-10 years Nitrous oxide (N2O) – Source: Industry and agriculture (fertilizers) Anthropogenic increase: 15% Average atmospheric residence time: 140-190 years
  12. 12. SummaryGreenhouse gases absorb infrared radiation and prevent itfrom escaping to space.Carbon dioxide, methane, and nitrous oxide are very goodat capturing energy at wavelengths that other compoundsmiss
  13. 13. Greenhouse Effect & Global Warming • The “greenhouse effect” & global warming are not the same thing. – Global warming refers to a rise in the temperature of the surface of the earth • An increase in the concentration of greenhouse gases leads to an increase in the the magnitude of the greenhouse effect. (Called enhanced greenhouse effect) – This results in global warming
  14. 14. Climate Change vs. Variability14.5 58.014.4 57.814.3 Variability 57.614.214.1 Average 57.414.0 57.213.9 57.013.8 56.813.7 56.613.6 56.413.5 56.213.4 1840 1860 1880 1900 1920 1920 1940 1960 1980 2000 (modified)
  15. 15. Climate Change vs. VariabilityClimate variability is natural.Even in a stable climate regime, there will alwaysbe some variation (wet/dry years, warm/coldyears) A year with completely “average” or“normal” climate conditions is rareThe challenge for scientists is to determinewhether any increase/decrease in precipitation,temperature, frequency of storms, sea level, due to climate variability or climate change.
  16. 16. Global Energy Redistribution
  17. 17. Radiation is not evenly distributed over theSurface of the earth. The northern latitudes have anenergy deficit and the low latitude/ equator has an excess.But the low latitudes don’t indefinitely get hotter and thenorthern latitudes don’t get colder.Why?The atmosphere and ocean transfer energy from lowlatitudes to high
  18. 18. AtmosphericPressureDecreasesWith Height Above 99%Most of theenergy iscapturedclose to the Above 90%surfaceThat energy Above 50%drives climateand weather Pressure (mb) 50 percent of mass of the atmosphere is within 6 km of the surface
  19. 19. Atmospheric Feedbacks POSITIVE NEGATIVE Increased CO2 More water vapor & other + changes Higher temperature + Increased cloud cover More water vapor More reflected solar radiation –More absorbed infrared radiation Lower temperature + + Higher temperature Less water vapor + More water vapor