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UMC Glenn Miller Ballroom 10-11:30

UMC Glenn Miller Ballroom 10-11:30. 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?

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UMC Glenn Miller Ballroom 10-11:30

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  1. UMC Glenn Miller Ballroom 10-11:30

  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? All power point images are only for the exclusive use of Phys3070/Envs3070 Spring term 2014

  3. Today The logic of carbon/climate, run like a criminal trial. Motive, means, opportunity, evidence. All power point images are only for the exclusive use of Phys3070/Envs3070 Spring term 2014 The logic

  4. 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) will change 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 may accelerate and amplify these changes, leading to large uncertainties.

  5. The evidence: • Current measurements of CO2 emissions and in the atmosphere, temperatures, sea levels. • Historical records, especially correlating past CO2, temperatures, sea levels. What is the relation between CO2 and temperature? • Molecular physics and radiative transport.

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

  7. All objects emit a continuum of ‘blackbody’ electromagnetic radiation. • Power emitted = area * universal constant (s) * 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

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

  9. << blue red>>

  10. TO the earth

  11. When that radiation hits a surface Some is reflected (albedo=fraction reflected) The rest is absorbed, heating that surface. Then that surface radiates by the same law ~T4.

  12. e depends on material-- Allows remote sensing or ‘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…..

  13. IF the earth were a bare 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.

  14. Black body earth temperature Earth emits from an area = 4p r2 Earth catches light from the sum by a fraction pr2 / 4p R2. With r = earth radius R = distance to the sun If ‘black’, T=278 deg K=5 deg C

  15. Surface 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.

  16. 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.

  17. FROM the earth =C?

  18. 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.

  19. CO2 H2O (causing cancer!)

  20. 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….

  21. The big point-- If the earth and its atmosphere trap more energy, then to balance energy in = energy out, the earth’s temperature must rise, making T4 more effective. The absorption of energy in the atmosphere is then the same fraction of a larger amount of energy emitted by the earth.

  22. Friday • Learning from the past—paleoclimate, trapped atmospheric bubbles, proxies for temperature, sea levels…..

  23. //www.ipcc.ch/ click on Summary for Policymakers, 33 dense pages.

  24. Mar 7 (F) Evidence from Paleoclimate, R and K 10.3, Begin reading the IPCC Summary for Policy Makers, www.ipcc.ch/ click on Summary for Policy Makers. This is a fact-filled 33 pages, 9 Megs long. Our classes for a while will be devoted to making sure you understand this document. Mar 10 (M) Climate change models HW #5 Mar 12 (W) Carbon wedges, a solution?; cmi.princeton.edu/wedges/intro.php; en.wikipedia.org/wiki/Stabilization_Wedges_Game/ Mar 14 (F) Geoengineering Mar. 17 (M) Carbon overview HW #6 Mar. 19 (W) Exam 2 *******change******* Mar. 21 (F) Introduction to renewable energy

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