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CWA. Today: 11:30-12:20 Rethinking American Power/ Macky 1-1:50 Communicating Climate Science; Why is this so Hard? / Macky Tuesday: 9:30-10:50 Truth about Energy Policy/ Old Main Chapel 3;30-4:50 The War on Science/G1b20. Global Climate Change.

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  1. CWA Today: 11:30-12:20 Rethinking American Power/Macky 1-1:50 Communicating Climate Science; Why is this so Hard? /Macky Tuesday: 9:30-10:50 Truth about Energy Policy/ Old Main Chapel 3;30-4:50 The War on Science/G1b20

  2. Global Climate Change Has our use of fossil fuels, the basis of much of human prosperity, doomed us to a significantly worse global climate? Is there anything we could do about this, without vast costs? Or even with vast costs?

  3. The logic: Burning fossil fuels, the accumulation of millions of years of solar energy, emits CO2, in large and increasing amounts. This CO2 (with other modern gases) changes the heat balance of the planet. The effects of this heat balance will be climate change, only partially predicable. There may be feedback mechanisms that will accelerate and amplify these changes.

  4. The evidence: • Current measurements of CO2, temperatures, sea levels. • Historical records, especially correlating past CO2, temperatures, sea levels. • Molecular physics and radiative transport.

  5. Today-the science basics • Laws of electromagnetic radiation- section 4.3 • Molecular physics These are NOT arguable!

  6. All objects emit a continuum of ‘blackbody’ electromagnetic radiation. • Power emitted = area x universal constant (s) x emissivity (e, characteristic of the surface, <1) x T4 • e=1  ‘black body’ • T in degrees Kelvin = deg C+273. • Sun 5250 deg C= 5523 deg K • Earth 20 deg C= 293 deg K • (5523/293)4=126,245

  7. Color • Wavelength of strongest emission = lmax = 2898/T (in micrometers = mm) Sun at 5523 deg K , lmax=0.525 mm = 525 nm =5250 A Earth at 293 deg K, lmax=9.89 mm=9890 nm, in the infrared. Refer to fig. 4.1

  8. When that radiation hits a surface Some is reflected (albedo=fraction reflected) Rest is absorbed, heating that surface. Then that surface radiates by the same law.

  9. e depends on material-- Allows ‘thermal mapping, If all of a region is at the same temperature, imagery can specify the nature of the surface- rock types, healthy/unhealthy crops, water…..

  10. IF the earth were a rock-- • Sun emits radiation, with some small fraction caught by the earth. • Earth warms from this, and emits, but into ALL directions. • At equilibrium, these balance, which happens at some temperature– easy to compute.

  11. Black body earth temperature Earth emits from an area = 4p r2 Earth catches light from the sum by a fraction pr2 / 4p R2. If ‘black’, T=278 deg K=5 deg C

  12. Albedo • Albedo = fraction of ‘light’ which is reflected. • Fresh snow—60-90% • Desert sand 30-50% • Forest 5-20% • Oceans 5-10% • Earth average 31%********** • So T 254 deg K=-19 deg C. • Play the albedo game, www.windows.ucar.edu/tour/link=/earth/climate/sun_radiation_at_earth.html.

  13. But-- • The earth has an atmosphere between the surface, where sunlight is absorbed, and open space. This material is NOT equally transparent to solar and earth emissions! • Passes solar radiation, absorbs earth’s radiation  a greenhouse effect. (named after the same effect due to glass) • Still in equilibrium, but requires a higher earth temperature.

  14. ALL molecules with three or more atoms are greenhouse gases. • A ‘greenhouse gas’ is a substance that is differentially transparent/absorptive to light of different wavelengths.

  15. movie //science.widener.edu/sub/ftir/ ir_co2.html

  16. Recap-- Temperature radiation ‘efficiency’ depends a bit on details, e=emissivity, and albedo=reflectivity. Radiation passing through a gas can be absorbed, heating the gas, sending less into space. That absorption depends on the gas, and in the earth’s thermal spectrum is dominated by molecules with three or more atoms—CO2, H2O, CH4….

  17. Wednesday • Consequences and feedbacks (example– warmer earth  less ice  lower albedo  more surface absorption  warmer earth….) • Why fuss about CO2?

  18. Revised HW for April 12 1. (6) Go to www.windows.ucar.edu/tour/link=/earth/climate/sun_ radiation_at_earth.html. After reading the ‘intermediate’ text, use the calculator provided to give the temperature of the earth at its current albedo of 0.31, and then recompute the temperature at an albedo of 0.35 (shinier) and 0.25 (darker).

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