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The Atmosphere: Part 8: Climate Change: Sensitivity and Feedbacks

The Atmosphere: Part 8: Climate Change: Sensitivity and Feedbacks. Composition / Structure Radiative transfer Vertical and latitudinal heat transport Atmospheric circulation Climate modeling. Suggested further reading: Hartmann, Global Physical Climatology (Academic Press, 1994).

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The Atmosphere: Part 8: Climate Change: Sensitivity and Feedbacks

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  1. The Atmosphere:Part 8: Climate Change: Sensitivity and Feedbacks • Composition / Structure • Radiative transfer • Vertical and latitudinalheat transport • Atmospheric circulation • Climate modeling Suggested further reading: Hartmann, Global Physical Climatology (Academic Press, 1994)

  2. A simple 2-box model • Two equal mass boxes, temperatures T1 and T2 • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr • Temperatures mixed with time constant τd

  3. A simple 2-box model • Two equal mass boxes, temperatures T1 and T2 • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr • Temperatures mixed with time constant τd radiation

  4. A simple 2-box model • Two equal mass boxes, temperatures T1 and T2 • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr • Temperatures mixed with time constant τd dynamics

  5. A simple 2-box model • Two equal mass boxes, temperatures T1 and T2 • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr • Temperatures mixed with time constant τd steady state solutions { where .

  6. Equilibria of 2-box model Fix Te, vary γ with polar ice Assumes ice in high latitude box (T2 < 263K)

  7. Equilibria of 2-box model with polar ice Assumes ice in high latitude box (T2 < 263K)

  8. Equilibria of 2-box model ice-free with polar ice Assumes ice in high latitude box (T2 < 263K) Assumes high latitude box is ice-free (T2 > 263K)

  9. Equilibria of 2-box model Ice-albedo feedback➙ multiple equilibrium states ice-free with polar ice Assumes ice in high latitude box (T2 < 263K) Assumes high latitude box is ice-free (T2 > 263K) multiple equilibria

  10. Equilibria of 2-box model Fix γ, vary Te T1 ice-free with polar ice T2

  11. A 1-D model (Budyko/Sellers)(T, ice edge, vary with latitude)

  12. Climate forcings and sensitivity in equilibrium, net incoming flux is Function of temperature, water vapor, clouds, CO2 and other greenhouse gases … Function of solar constant, albedo (ice cover, cloudiness, vegetation, …) } Climate forcing due to ith process (all else held fixed) = δQ (e.g., [CO2] doubling to 600ppm ➙ δQ = 4 Wm-2)

  13. Climate forcings and sensitivity in equilibrium, net incoming flux is Function of temperature, water vapor, clouds, CO2 and other greenhouse gases … Function of solar constant, albedo (ice cover, cloudiness, vegetation, …) } ➙ climate sensitivity Climate forcing due to ith process (all else held fixed) = δQ (e.g., [CO2] doubling to 600ppm ➙ δQ = 4 Wm-2) feedbacks

  14. Radiative response only(no feedbacks) Suppose Te = Ts - constant (Te = 255 K) ➙ (Need doubling of CO2 or 1.6% increase of solar constant to produce 1K warming)

  15. Water vapor feedback -4 Wm-2K-1 +2Wm-2K-1 w.v. feedback

  16. Ice albedo feedback (overestimate — have neglected clouds) -4 Wm-2K-1 +2 Wm-2K-1

  17. Cloud feedback Current climate: cloud amount ~ 50% 10% increase in Ac ➙ would offset CO2 doubling

  18. Past T trend simulated by 3D coupled atmosphere-ocean models

  19. Predicted ΔT for doubled CO2 from 3 different coupled 3D atmosphere-ocean models

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